learndrugs

Labs & diagnostics by disorder

What each test shows in the disease, beside the normal range it departs from — every disorder's diagnostics table in one place. Values are typical adult figures for orientation; always read against your facility's reference ranges. For therapeutic and toxic drug levels, see Lab values & drug levels.

1103 findings · 167 disorders
Foundations Cardiovascular Respiratory Nervous Mental & Behavioral Health Endocrine Digestive / GI Renal / Genitourinary Hematologic Immune / Infectious Musculoskeletal Integumentary Reproductive & OB Sensory Oncology

Foundations

Fluid & Electrolyte Imbalances
Serum sodium StatPearls
< 135 mEq/L = hyponatremia (severe < 125) · > 145 mEq/L = hypernatremia Reference ranges vary by agency and lab — always read against your facility’s range. During correction, recheck every 2–4 h
Normal 135–145 mEq/L
Serum potassium StatPearls
< 3.5 mEq/L = hypokalemia (severe < 2.5) · > 5.0–5.5 mEq/L = hyperkalemia An unexpected high K⁺ is most often hemolysis in the tube (pseudohyperkalemia) — redraw before treating aggressively. A real high K⁺ gets an ECG first
Normal 3.5–5.0 mEq/L
Serum calcium (total) StatPearls
Low in hypocalcemia; hypercalcemia grading: mild 10.5–11.9 · moderate 12.0–13.9 · crisis 14.0–16.0 mg/dL Correct for albumin: total Ca²⁺ falls ~0.8 mg/dL per 1 g/dL drop in albumin below 4 g/dL while ionized calcium stays normal — check albumin before calling it true hypocalcemia
Normal ~8.6–10.2 mg/dL (varies by lab)
Serum magnesium Open RN
Low with diuretics, diarrhea, PPIs, alcohol use; high in renal failure and obstetric MgSO₄ therapy Check magnesium in every refractory hypokalemia or hypocalcemia — neither corrects until magnesium is replaced
Normal 1.5–2.4 mEq/L (units and ranges vary by lab)
ECG / telemetry StatPearls
Hypokalemia: flat T, ST depression, U wave, long QT · Hyperkalemia: peaked T → lost P → wide QRS → sine wave · Hypercalcemia: short QT · Hypocalcemia: long QT The ECG is the first diagnostic step in hyperkalemia and the reason continuous monitoring is required during IV potassium above 10 mEq/h
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Volume-status workup
FVD: urine Na⁺ < 20 mEq/L, elevated BUN/creatinine ratio, hemoconcentration (relative polycythemia), elevated lactate if tissues are hypoxic Pair the labs with the bedside numbers: strict I&O and the daily weight (1 kg = 1 L)
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Acid–Base Imbalances & ABGs ABG
pH (arterial) StatPearls
< 7.35 = acidemia · > 7.45 = alkalemia; within range, compare against 7.40 for the stepwise read Step ① of every ABG. A normal pH does not mean a normal gas — full compensation and mixed disorders both hide behind it
Normal 7.35–7.45
PaCO₂ StatPearls
> 45 = respiratory acidosis side · < 35 = respiratory alkalosis side — the respiratory (acid) parameter ROME: Respiratory Opposite — CO₂ and pH move in opposite directions when the problem is respiratory
Normal 35–45 mm Hg
HCO₃⁻ (bicarbonate) StatPearls
Below normal in metabolic acidosis · above normal in metabolic alkalosis — the metabolic (base) parameter ROME: Metabolic Equal — HCO₃⁻ and pH move in the same direction when the problem is metabolic
Normal 22–26 mEq/L
PaO₂ / SaO₂ StatPearls
Assessed as step ④ of the read — an ABG interpretation is incomplete without the oxygenation check Reference figures per StatPearls; some nursing texts print PaO₂ 80–100
Normal PaO₂ 75–100 mm Hg · SaO₂ 95–100%
Anion gap StatPearls
Elevated in ketoacidosis, lactic acidosis, renal failure, and toxic ingestions; normal (hyperchloremic) with diarrhea or renal tubular acidosis Correct for albumin: the gap falls ~2.5 mEq/L per 1 g/dL of albumin below normal — a hidden gap in the hypoalbuminemic patient
Normal 8–12 mEq/L (Na⁺ − [Cl⁻ + HCO₃⁻])
Urine chloride (metabolic alkalosis workup) StatPearls
< 10 mEq/L = chloride-responsive (GI losses, diuretics, post-hypercapnia) · > 20 mEq/L = chloride-resistant (hyperaldosteronism, Bartter/Gitelman) Sorts the alkalosis that will respond to saline + K⁺ repletion from the one that needs its underlying disease treated
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Shock States
Serum lactate StatPearls
> 2 mmol/L = hyperlactatemia; > 4 mmol/L = lactic acidosis. Rises with hypoperfusion before the BP falls — it detects occult, compensated shock Both a risk marker and a therapeutic target — the higher and the longer elevated, the greater the mortality risk; repeat measurements track the response to resuscitation
Normal < 2 mmol/L (critical illness)
Mean arterial pressure (MAP) StatPearls (Surviving Sepsis Campaign target)
< 65 mmHg is the perfusion floor for heart and kidneys; septic shock = vasopressors needed to hold MAP with lactate > 2 mmol/L despite fluids MAP < 50 mmHg threatens brain perfusion — intervene immediately. In septic shock in adults aged 65 or older, SSC 2026 suggests a lower initial target of 60–65 mmHg. Spinal cord injury is the other exception: StatPearls cites an SCI-specific target of 85–90 mmHg for the first 7 days to perfuse the cord
Normal ≥ 65 mmHg
Urine output
< 0.5 mL/kg/hr signals hypoperfusion; < 30 mL/hr suggests renal hypoperfusion / early shock; cardiogenic criteria use ≤ 30 mL/hr Hourly output is the nurse’s continuous perfusion monitor — trend it, don’t snapshot it
Normal > 0.5 mL/kg/hr (> 30 mL/hr)
Blood gas + bicarbonate
Metabolic acidosis as shock progresses; frank lactic acidosis often shows pH < 7.35 with bicarbonate < 20 mmol/L Tachypnea is the respiratory compensation you can see before the ABG comes back
Normal pH 7.35–7.45
Hemodynamic profile (CVP · CO · SVR) StatPearls
Hypovolemic: ↓ CVP · ↓ CO · ↑ SVR — Cardiogenic: ↑ CVP · ↓ CO · ↑ SVR — Distributive: ↓ CVP · ↑ CO · ↓ SVR — Neurogenic: all ↓ The direction pattern names the shock class when the bedside picture is ambiguous; cardiogenic criteria add cardiac index ≤ 2.2 L/min/m² with wedge pressure > 15 mmHg
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Point-of-care ultrasound (RUSH) · echo
Evaluates cardiac function and fluid status; echocardiography is the preferred bedside modality for tamponade Standard workup also includes CBC, renal/liver panels, cardiac biomarkers, coagulation profile, type and screen, and cultures before antibiotics
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Sepsis & Septic Shock
Serum lactate Surviving Sepsis Campaign (via StatPearls)
> 2 mmol/L = hyperlactatemia (the septic-shock lactate criterion); > 4 mmol/L = critical — lactic acidosis, often with pH < 7.35 and HCO₃⁻ < 20 mmol/L Remeasure if the initial level is elevated and resuscitate to a falling lactate — 2-hour lactate clearance independently predicts survival; higher and longer-elevated lactate means greater mortality
Normal < 2 mmol/L
Blood cultures ×2 sets
Drawn before antibiotics — two sets in 4 bottles (2 aerobic + 2 anaerobic), 8–10 mL per bottle, ≈ 30–40 mL total Never delay antibiotics for the draw — but cultures taken after antibiotics have started lose their yield, and with it the chance to de-escalate therapy
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SOFA score Sepsis-3 (2016)
An acute increase of ≥ 2 points = the organ dysfunction that defines sepsis; tracks six systems — lungs (PaO₂/FiO₂), coagulation (platelets), liver (bilirubin), cardiovascular (MAP/pressors), CNS (GCS), renal (creatinine) The best predictor of in-hospital mortality in ICU sepsis. A revised score, SOFA-2 (2025), updates several organ subscores for modern ICU practice, but the Sepsis-3 definition is still anchored to the original SOFA
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qSOFA (bedside) Sepsis-3 (2016)
SBP ≤ 100 mmHg · RR ≥ 22/min · GCS < 15 — 1 point each; ≥ 2 associated with poor outcomes A risk-stratifier, not a stand-alone screen — SSC 2026 recommends NEWS/NEWS2, MEWS or SIRS over qSOFA as a single screening tool, because qSOFA has limited sensitivity for early sepsis
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Organ-dysfunction panel
Creatinine > 2.0 mg/dL or urine output < 0.5 mL/kg/hr (AKI) · bilirubin > 2 mg/dL · platelets < 100,000/µL · INR > 1.5 or aPTT > 60 s These trends tell you which organs are failing — falling platelets with a rising INR should raise the question of DIC
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Procalcitonin (PCT)
Elevated as an inflammatory marker Not used to decide when to start antibiotics; serial PCT < 0.5 µg/L or a > 80% fall from peak supports stopping them earlier
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Inflammation, Infection & Healing
C-reactive protein
Normally below 5 mg/L. After a stimulus, CRP concentrations "rise WITHIN HOURS, DOUBLING WITHIN 5 TO 8 HOURS." The bands: "MILD inflammation and VIRAL infections cause CRP concentrations to elevate within the range of 10 to 40 mg/L. In contrast, ACTIVE inflammation and BACTERIAL infection result in 40 to 200 mg/L concentrations" CRP is an acute-phase reactant made in the liver, "directly regulated by interleukin-6," which "can bind to bacteria and tissue membranes, enhancing PHAGOCYTOSIS," and can activate the classical complement pathway. A normal CRP hours after an insult may simply be too early to have doubled. One laboratory artefact matters: extreme elevations can produce "falsely low results due to overwhelming antigen excess — this PROZONE EFFECT" in some nephelometric and turbidimetric methods
Normal Below 5 mg/L
High-sensitivity CRP — a different question
Used "to evaluate increased CARDIOVASCULAR DISEASE risk," where raised plasma hs-CRP is a risk factor alongside LDL cholesterol and metabolic syndrome. There are two assays — "a standard assay and a HIGH-SENSITIVITY assay" — and they answer different questions The evidence is genuinely unsettled and should be taught that way: "it remains UNCERTAIN whether CRP plays an ACTIVE role in causing heart disease or if lowering hs-CRP is a valid goal." The 2018 CANTOS trial found that lowering hs-CRP with canakinumab "decreased major cardiovascular events by 25%," mainly in patients brought below 2 mg/mL — yet a large study found simvastatin’s effectiveness was unaffected by baseline CRP
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Erythrocyte sedimentation rate Westergren method, adopted as the gold standard by the ICSH in 1973, as reported by StatPearls
"The ESR measures the DISTANCE IN MILLIMETERS that red blood cells settle in a VERTICAL COLUMN of anticoagulated blood over 1 HOUR." It "rises WITHIN 24 TO 48 HOURS of the onset of inflammation and GRADUALLY DECREASES as the inflammation resolves" The mechanism explains every confounder. "In inflammatory conditions, elevated plasma protein levels enhance ROULEAUX FORMATION, causing red cells to aggregate and settle more rapidly" — so the ESR is "a PHYSICAL measure of RBC AGGREGATION influenced by plasma protein interactions rather than a direct assay." It is therefore "influenced by age, gender, pregnancy, anemia, red blood cell dysmorphia, obesity, and fibrinogen deficiency," and conditions such as polycythemia lower it, producing "a lower than expected value despite a significant underlying inflammatory state." Its "use as a screening test in asymptomatic persons is limited by its LOW SENSITIVITY AND SPECIFICITY"
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CRP versus ESR — which to believe, and when
CRP rises within hours and doubles every 5 to 8 hours; ESR takes 24 to 48 hours to rise and falls gradually. CRP is a direct assay of a liver-made protein driven by IL-6; ESR is an indirect physical measure of red-cell aggregation driven by plasma proteins CRP is also the more robust specimen: "common laboratory variables such as specimen type, delays in specimen processing, and storage temperature have minimal effects," whereas the ESR is confounded in both directions by patient factors. The practical rule that follows: CRP tracks the acute change, ESR tracks the slower trend — and a normal ESR at 12 hours tells you nothing because it has not had time to move. Procalcitonin is the third named marker, "typically less than 0.1 ng/mL in healthy individuals"
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White cell count and the differential
"In adults, a WBC count exceeding 11,000 cells/µL is generally considered leukocytosis, whereas a count greater than 100,000 cells/µL is termed HYPERLEUKOCYTOSIS." But "NORMAL THRESHOLDS VARY BY AGE AND PHYSIOLOGICAL STATE — for example, a WBC count of 30,000 cells/µL would be abnormal in adults but may fall within the normal range for a newborn" The subtype is the information. "Evaluation of the WBC differential can help identify the underlying etiology — for example, EOSINOPHILIA may suggest ALLERGIC OR PARASITIC conditions, whereas LYMPHOCYTOSIS is often seen in VIRAL INFECTIONS, AUTOIMMUNE DISEASES, AND HYPERTHYROIDISM." Causes include "infection, inflammation, allergic reactions, malignancy, and hereditary disorders" — a high count is not a diagnosis of infection
Normal Leukocytosis in adults above 11,000 cells/µL
Band forms — the mechanism behind the immature cells
"During neutrophil development, myeloblasts differentiate into promyelocytes, then myelocytes, and subsequently metamyelocytes. Metamyelocytes no longer undergo mitosis and mature into BAND FORMS. These cells may be released into the circulation, where they account for approximately 3% TO 5%" of circulating white cells The trigger is stated plainly: "in response to STRESS, INFECTION, OR INFLAMMATION, polymorphonuclear cells, BAND FORMS, and METAMYELOCYTES ENTER THE CIRCULATION and migrate to the necessary sites." The conventional name for that finding is a left shift, but no source behind this page uses the phrase, so the mechanism is what is taught here — and the numeric threshold of more than 10% bands belongs to the sepsis page’s white-cell criterion
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Four routes to a high white count — only one needs a pathogen
"Leukocytosis may result from INCREASED LEUKOCYTE PRODUCTION, DECREASED REMOVAL from the circulation, DEMARGINATION, or RELEASE FROM STORAGE COMPARTMENTS. Demargination refers to the mobilization of cells, which is mediated by the effects of external factors on ADHESION MOLECULES" Demargination is the sourced reason a steroid dose or acute stress raises the white count with no infection at all. A further trap is the leukemoid reaction — "a transient and marked increase in WBC count, typically… greater than 50,000 cells/µL without a myeloproliferative neoplasm," caused by "medications, asplenia, nonhematologic malignancies, and infection caused by Clostridioides difficile, tuberculosis, pertussis, and visceral larva migrans," which "can be mistaken for leukemia." Hyperleukocytosis and leukostasis are a medical emergency requiring immediate treatment
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Measuring the temperature properly
The site changes the number: "the average AXILLARY temperature reading is 35.97 °C, ORAL is 36.57 °C, urine is 36.61 °C, TYMPANIC is 36.64 °C, and RECTAL is 37.04 °C." Normal is approximately 37 °C, varying by about 0.5 °C through the day, with a fever usually being a rise greater than 0.5 °C. The bands given are low-grade 37.3–38.0, moderate 38.1–39.0, high-grade 39.1–41, and hyperthermia above 41 °C Two honest caveats come with those numbers. The source states its own bands "may vary slightly based on the source," and concludes that "given the many factors influencing the results… THERE CAN NEVER BE A SINGLE, UNIVERSALLY ACCEPTED TEMPERATURE CUTOFF DEFINING A FEVER. This clinical reality, however, does not remove the need for PRECISION." And palpation is not a measurement — "the diagnosis of fever based on PALPATION is UNRELIABLE AND INACCURATE IN UP TO 40% of individuals. If a fever is suspected, an OFFICIAL READING SHOULD BE OBTAINED"
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Systemic inflammatory response criteria
Owned by the Sepsis page, and deliberately not restated here. What this page supplies is the mechanism that makes a systemic inflammatory response coherent — the mediator cascade of the pathophysiology section firing at scale rather than locally The source itself makes the bridge: acute inflammation is "an immediate, adaptive response… this BENEFICIAL response protects against infectious organisms… However, it can become DETRIMENTAL if not regulated, such as seen in SEPTIC SHOCK." Go to the sepsis page for the criteria, their Sepsis-3 status, and the bundle — printing them twice in one ledger is how two pages drift apart
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Cellular Adaptation & Injury Cell injury & cell death
Tissue biopsy — microscopic appearance
Hyperplasia: more cells that look normal. Dysplasia: abnormal cells and disordered tissue, graded mild, moderate or severe. Carcinoma in situ: abnormal cells that do not invade. Cancer: invasion. The grade depends on "how abnormal the cells look under a microscope and how much of the tissue or organ is affected."
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Esophageal biopsy in Barrett esophagus
Salmon-colored mucosa at least 1 cm above the gastroesophageal junction; biopsy shows columnar epithelium and goblet cells (intestinal metaplasia). Follow-up is based on whether there is no dysplasia, indeterminate, low- or high-grade dysplasia, or invasive adenocarcinoma. See the GERD page.
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Monitoring after revascularization
Coagulation profile, electrolytes, strict intake and output (renal function); after MI, repeat ECGs and echocardiography. The patient "should be placed under strict observation" — reperfusion injury can appear as arrhythmias, cerebral changes, a painful limb or multi-organ failure.
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Limb perfusion assessment (pulses, capillary refill, color)
Ischemia: non-palpable distal pulses, delayed capillary refill, dependent rubor with pallor on elevation, hair loss. In diabetes, neuropathy can hide developing gangrene — inspect, do not rely on the patient feeling it.
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Pain Physiology & Assessment Pain assessment
Patient self-report
The standard — "Self-report is the most reliable way to assess pain intensity." AHRQ: "When the patient is able to report pain, the patient’s behavior or vital signs should never be used in lieu of self-report." Open RN, relaying IASP: "A person’s report of an experience as pain should be respected."
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Numeric Rating Scale (NRS)
0 (no pain) to 10 (worst possible pain) A screen, not a full assessment — StatPearls: "Focusing solely on a numerical pain score proves inadequate." Adolescents can usually use a numeric scale like adults. Pair the score with a comfort-function goal: the pain level at which the patient can do what they need to, such as walking after surgery.
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PQRSTU / OLDCARTES
Provocative/Palliative, Quality/Quantity, Region/Radiation, Severity, Timing/Treatment, Understanding Structured questions for a full assessment (OLDCARTES: onset, location, duration, characteristics, aggravating factors, radiating, treatment, effect, severity). Use follow-up questions when answers do not line up, and ask how pain affects daily function.
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Wong-Baker FACES scale
Children and others who cannot rate pain on 0–10 The patient chooses the face that matches how they feel — the nurse does not pick a face from the patient’s expression. The scale is copyrighted; use the licensed form.
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FLACC (Face, Legs, Activity, Cry, Consolability)
Five items scored 0–2; total 0–10 Open RN: for children between 2 months and 7 years or individuals who cannot verbally communicate pain.
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PAINAD (Pain Assessment in Advanced Dementia)
Items scored 0–2; total 0 (no pain) to 10 (severe pain) For noncommunicative patients with advanced dementia (Open RN).
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CPOT (Critical-Care Pain Observation Tool) Afenigus 2024 review
Four indicators (facial expression, body movements, muscle tension, ventilator compliance) scored 0–2; total 0–8 For ICU adults who cannot self-report, ventilated or not; harder to interpret in severe neurological injury or deep sedation.
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Behavioral Pain Scale (BPS) · COMFORT Behavioral Scale
BPS: facial expression, upper-limb movement, ventilator compliance · COMFORT-B: children of any age on mechanical ventilation AHRQ: "No research as yet confirms that a pain behavior score is a pain intensity score." Physiologic signs vary in sensitivity; StatPearls: "None should be used in isolation."
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When the patient cannot self-report — the hierarchy
Painful condition or procedure → pain behaviors → reports from family or caregivers If any suggests pain, assume pain is present; where appropriate give a trial analgesic dose and compare behavior before and after (AHRQ).
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Reassessment after an analgesic AHRQ
IV opioids 15–30 minutes; oral opioids and nonopioids 45–60 minutes AHRQ: "IV opioids are reassessed in 15–30 minutes, whereas oral opioids and nonopioids are reassessed 45–60 minutes after administration." Open RN: reassess in about an hour or on a time frame set by the route, onset and peak; if pain is above the comfort-function goal, intervene and follow up within 1 hour. AHRQ relays the American Pain Society: "The American Pain Society suggests that pain be the fifth vital sign as a means of prompting nurses to reassess and document pain whenever vital signs are obtained."
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Sedation level and respiratory status (opioids) AHRQ
Awake or easily roused = acceptable; frequently drowsy and drifting off = reduce the opioid; minimal or no response = stop the opioid and give naloxone per protocol AHRQ describes the Pasero Opioid-induced Sedation Scale for opioid-naive patients starting opioids, checked at least every 2 hours for the first 24 hours. Check sedation and breathing before each additional dose.
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Heat-Related Illness Heat stroke
Core (rectal) temperature
Heat stroke: typically > 40 °C (StatPearls); mental status is the discriminator "a core temperature should be obtained with rectal thermometry if clinically possible." During cooling, core temperature "should be continuously monitored with a rectal or esophageal probe."
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Creatine kinase, urine myoglobin
Elevated with rhabdomyolysis "Creatinine kinase levels to evaluate for skeletal muscle injury and rhabdomyolysis"; rhabdomyolysis is "more common in exertional heat stroke."
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Electrolytes, glucose, kidney and liver tests
Hyperkalemia, hypocalcemia, hypoglycemia, ↑ creatinine, ↑ AST/ALT "patients with heat illness frequently have hypoglycemia and may require carbohydrate replacement." "In classic heat stroke, elevated aspartate aminotransferase and alanine aminotransferase levels are the most commonly reported laboratory abnormalities."
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CBC, PT, aPTT
Coagulopathy / DIC in heat stroke Heat stroke labs include "a complete blood count, comprehensive metabolic panel, prothrombin time, activated partial thromboplastin time, blood gases, serum creatine phosphokinase level, and urine myoglobin measurement."
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Blood gases
Classic: respiratory alkalosis; exertional: may add lactic acidosis "In classic heat stroke, respiratory alkalosis predominates, whereas exertional heat stroke may also involve concomitant lactic acidosis."
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ECG
ST depression, QT prolongation, T-wave changes possible Continuous cardiac monitoring during cooling "is recommended when available."
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Hypothermia & Frostbite Accidental hypothermia
Core temperature — low-reading probe
Mild 32–35 °C · moderate 28–32 °C · severe < 28 °C (StatPearls) "most commercially available thermometers cannot read under 35 °C. Standard tympanic infrared thermometers are also unreliable." "The esophageal thermometer is the most accurate method of determining core temperature in critically ill and intubated patients"; rectal readings "can take up to 1 hour to reflect changes during rewarming."
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ECG and continuous cardiac monitoring
Bradycardia, atrial fibrillation, prolonged PR/QRS/QT, Osborn (J) wave "Electrocardiography (ECG) should be obtained in all patients with hypothermia because cardiac conduction abnormalities and dysrhythmias are common."
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Finger-stick glucose, CBC, basic metabolic panel
Hypoglycemia possible; ↑ Hgb/Hct from cold diuresis; potassium abnormalities "A rise in hemoglobin and hematocrit may be due to cold diuresis." Potassium "should not be used as the sole criterion for terminating resuscitative efforts."
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Coagulation studies
May look normal despite coagulopathy "Coagulation studies may appear normal despite clinically significant coagulopathy because laboratory testing is typically performed at 37 °C."
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Search for other causes
Sepsis, hypothyroidism, adrenal insufficiency, hypoglycemia, intoxication, overdose Consider when the presentation "appears disproportionate to the degree of hypothermia," or when the patient fails to rewarm.
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[FROST] Technetium-99m bone scan / angiography
Defines extent of deep injury "Frostbite is a clinical diagnosis." Imaging "may help determine the extent of injury without waiting months for development of the line of demarcation" and may assist in selecting thrombolytic therapy.
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Drowning Nonfatal drowning
History of the event
Submersion time, rescue time, pulse lost?, CPR given? StatPearls: "Key details include the estimated duration of submersion, length of rescue or extraction time, whether a pulse was lost, and whether rescue breathing or cardiopulmonary resuscitation (CPR) was initiated." "Duration of submersion is the most critical determinant of survival, with markedly increased mortality when submersion exceeds 5 minutes."
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Pulse oximetry and continuous monitoring
Oxygen saturation, consciousness, respiratory effort, pulse StatPearls: "Continuous monitoring of consciousness, respiratory effort, and pulse guides decisions for escalation."
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Chest x-ray and arterial blood gas
Only for persistent hypoxemia or progressive symptoms StatPearls: "Drowning is primarily a clinical diagnosis. Laboratory and imaging studies are not routinely indicated in well-appearing, asymptomatic patients with normal oxygenation." The initial chest x-ray "has limited correlation with clinical course or outcome."
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Altered mental status work-up
Head CT, glucose, ABG, toxicology, ethanol, metabolic panel StatPearls: "The most frequent laboratory abnormality is metabolic acidosis, typically due to lactic acidosis. Electrolyte disturbances are uncommon in nonfatal drowning."
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Core temperature
Hypothermia below 35 °C; mild 32–35, moderate 28–32, severe below 28 °C StatPearls (Hypothermia): "Core body temperature must be obtained immediately, as it is critical for determining appropriate management." "Oral temperature is only useful in ruling out hypothermia, as most commercially available thermometers cannot read under 35 °C."
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ECG
Dysrhythmias, conduction changes StatPearls (Hypothermia): "Electrocardiography (ECG) should be obtained in all patients with hypothermia because cardiac conduction abnormalities and dysrhythmias are common."
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Bites & Envenomation Animal bites
Bite history
Time, place, provoked or not, species, animal's health and vaccination, where it is now StatPearls: "Determine if the bite was provoked or unprovoked, as unprovoked attacks may raise concerns about rabies risk." Review "allergies; immunosuppressive conditions" and "tetanus and rabies vaccination status."
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Wound exam
Infection signs; nerve, vessel, tendon or joint injury; embedded teeth StatPearls: "Assess for any nerve or vascular injury by evaluating sensation, motor function, and distal pulses." "Test the movement of affected and adjacent joints to detect potential tendon or joint involvement."
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X-ray; wound culture
Fracture, retained tooth fragments, gas; organism if infected StatPearls: radiographs detect bone involvement, "retained foreign bodies, such as teeth fragments or debris," and gas; culture before antibiotics "If there are signs of infection."
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Pit viper labs
CBC, PT, INR, PTT, fibrinogen — repeated at the end of observation StatPearls, citing the Wilderness Medical Society: "All potential victims of pit viper envenomation should have a complete blood count (CBC), partial thromboplastin time (PTT), prothrombin time (PT), international normalized ratio (INR), and fibrinogen level checked where available."
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Serial swelling measurements
Leading edge marked with the time; circumference every 15–30 minutes StatPearls: "Place an ink mark on the proximal edge of the bite swelling as a baseline for serial measurements." "Measure the swelling extension and record circumference every 15 to 30 minutes"; hourly after four measurements without progression.
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Compartment pressure (if suspected)
> 30 mm Hg consistent with early compartment syndrome StatPearls (Crotalidae Envenomation): diagnosis should not rely on "soft" signs "but should be through direct compartment pressures or evidence of neurovascular compromise where direct pressures are unobtainable." "Compartment syndrome is a rare but serious complication of pit viper envenomation."
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Brown recluse: urinalysis; labs if systemic
Hemoglobinuria / hemolysis StatPearls: "At a minimum, one should obtain a urinalysis at the initial visit if the working diagnosis is a brown recluse spider bite and the patient is being discharged." Labs otherwise only "if there are systemic complaints, especially in children."
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Cardiovascular

Hypertension & Hypertensive Crisis HTN
Office blood pressure AHA/ACC 2025
≥ 130/80 mm Hg on at least two measurements on two separate occasions = hypertension · higher than 180/120 = crisis Technique decides the diagnosis: seated quietly ≥ 5 minutes, cuff bladder covering 80% of arm circumference. Treatment target for most adults: < 130/80
Normal < 120 and < 80 mm Hg
Ambulatory / home BP monitoring StatPearls
ABPM thresholds: daytime ≥ 135/85 · nighttime ≥ 120/70 · 24-hour ≥ 130/80 ABPM is described as the most accurate way to diagnose hypertension, and it unmasks both white-coat and masked hypertension — office numbers mislead in both directions; home and ambulatory monitoring are both recommended to confirm the diagnosis
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Urine albumin-to-creatinine ratio StatPearls
Albuminuria = early hypertensive kidney damage Part of the baseline hypertension workup — the kidney announces target-organ damage before creatinine moves
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ECG & echocardiography
Left ventricular hypertrophy — the heart’s structural answer to years of afterload In a crisis the ECG has a sharper job: "to ensure the patient is not having a heart attack" — pair it with cardiac enzymes
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Crisis workup (suspected emergency)
Metabolic panel, urinalysis, BNP, cardiac enzymes — hunting acute target-organ damage Add head CT for neurologic complaints, CXR for dyspnea, CT angiography for suspected aortic dissection
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Fundoscopic (retinal) exam
Chronic: retinopathy/maculopathy · crisis: papilledema and flame-shaped hemorrhages Papilledema at a crisis-level BP is target-organ damage you can see — it moves the patient to the emergency arm
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Coronary Artery Disease & Stable Angina CAD
Resting 12-lead ECG
ST-segment/T-wave changes with active ischemia; may show evidence of prior MI Cheap, fast, and not user-dependent — the first test during any chest-pain episode. It detects active ischemia, so a normal tracing while pain-free does not exclude CAD
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Exercise (treadmill) stress test StatPearls
ST-segment depression ≥ 1 mm indicates ischemia; patient exercises to 85% of age-predicted maximal heart rate Know the abort criteria: exertional hypotension, BP > 200/110 mm Hg, ST elevation or depression, or ventricular/supraventricular arrhythmias
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Troponin StatPearls
Normal (or minimally elevated) in unstable angina; elevated in NSTEMI — the lab that separates the two Drawn during acute chest pain to rule out MI
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Lipid panel StatPearls
The key chronic-setting lab. LDL-C goal < 70 mg/dL for stable ischemic heart disease (< 55 mg/dL for the highest-risk patients) Prognostic and a teaching anchor — an LDL above goal on a statin is a follow-up finding, not background noise
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Coronary artery calcium (CAC) score StatPearls
A score of 0 in symptomatic patients excludes obstructive CAD in 98.2% of cases Recommended for intermediate-risk patients (10-year ASCVD risk 7.5% to < 20%) and selected borderline-risk patients
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Coronary angiography (cardiac catheterization) StatPearls
The gold standard — the most accurate modality for evaluating ischemic CAD; FFR ≤ 0.80 or iFR ≤ 0.89 marks a hemodynamically significant intermediate (40–70%) stenosis Done under moderate sedation; watch for the complications — severe allergic reactions and kidney injury
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Acute Coronary Syndrome & MI ACS
12-lead ECG (within 10 minutes) 2025 ACC/AHA ACS guideline
STEMI: new ST elevation at the J point in ≥ 2 contiguous leads — ≥ 1 mm in most leads; in V2–V3, men ≥ 40 y need ≥ 2 mm, men < 40 y ≥ 2.5 mm, women ≥ 1.5 mm — often with reciprocal ST depressions. NSTE-ACS: ST depression, T-wave inversion, transient elevation — or a normal tracing Obtained and interpreted within 10 minutes of first medical contact. A normal ECG never rules out MI (one nursing review puts sensitivity near 30% despite 95–97% specificity) — repeat serial ECGs if the first is nondiagnostic with ongoing symptoms
Normal No acute ST-segment or T-wave changes
High-sensitivity cardiac troponin (hs-cTn) Fourth Universal Definition of MI
MI = a rise and/or fall with ≥ 1 value above the 99th-percentile upper reference limit plus evidence of ischemia. Kinetics: begins rising 3–4 h after symptom onset, peaks 24–48 h; troponin I stays up 7–10 days, troponin T up to 14 days The biomarker of choice — order troponin only, not multi-marker panels. Serial hs-cTn algorithms (0/1 h, 0/3 h) can rule in or out within 1–3 h; a negative troponin at 6 h effectively excludes infarction in most cases. Elevated troponin = myocardial injury, not automatically MI — it also rises in myocarditis, HF, PE, sepsis, and end-stage renal disease
Normal Below the assay’s 99th-percentile upper reference limit
CK-MB
Rises ~4 h post-injury, peaks ~24 h, normalizes by 48–72 h Its fast clearance made it the historical marker for detecting reinfarction while troponin is still elevated from the first event
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Risk scores — TIMI · GRACE · HEART
TIMI predicts 14-day adverse events from 4.7% (score 0–1) to 40.9% (score 6–7); GRACE predicts in-hospital and 6-month mortality; HEART was built specifically for ED chest-pain patients They stratify who needs an early invasive strategy — but no score definitively beats clinician judgment
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Cardiac catheterization 2025 ACC/AHA ACS guideline
The gold standard for NSTE-ACS — defines the anatomy and delivers PCI; early PCI is recommended for elevated-risk patients Radial access is now preferred over femoral (less bleeding, fewer vascular complications, lower mortality). Post-cath nursing: check the access site for hematoma and palpate distal pulses
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Heart Failure HF
BNP / NT-proBNP StatPearls
Elevated, tracking severity. In acute dyspnea, BNP < 100 pg/mL or NT-proBNP < 300 pg/mL makes HF unlikely — the rule-out numbers to know Runs high with renal failure, ACS, and age; low with obesity — trend the individual patient rather than comparing across patients
Normal BNP < 100 pg/mL
Echocardiogram (LVEF) AHA/ACC/HFSA 2022
The defining test — ≤ 40% = HFrEF · 41–49% = mildly reduced · ≥ 50% = HFpEF Initial modality of choice; also shows structure, wall motion, valves
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Chest X-ray
Enlarged cardiac silhouette, basal edema, vascular congestion, Kerley B lines A clear film does not exclude HF
Normal —
Electrolytes & renal function
K⁺ and creatinine move with treatment — diuretics waste potassium; ACE inhibitors/ARBs and MRAs retain it; creatinine rises in cardiorenal syndrome Trend with every diuretic or RAAS-blocker change
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ECG
May show prior infarction, chamber enlargement, conduction delay, or the atrial fibrillation that decompensated the patient
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Dysrhythmias Arrhythmias
12-lead ECG — rate & regularity
Bradyarrhythmia < 60 bpm · tachyarrhythmia > 100 bpm; regular vs irregular pattern narrows the differential Any irregular pulse found on exam requires an ECG for final diagnosis — the fingers screen, the ECG names the rhythm
Normal Normal sinus rhythm, 60–100 bpm
QRS width (origin of the rhythm) StatPearls
Narrow < 120 ms = supraventricular · wide ≥ 120 ms suggests ventricular origin — and ~70–80% of wide-complex tachycardias are VT When in doubt, treat a wide-complex tachycardia as VT — the odds say it is
Normal < 120 ms (< 0.12 s)
Atrial waveforms — afib vs flutter StatPearls
Afib: no distinguishable P waves, irregularly irregular, ventricular rate usually 80–180 · Flutter: “sawtooth” waves at ~300/min, classically 2:1 conduction → ventricular rate 150/min A regular narrow tachycardia sitting at exactly ~150 should make you hunt for buried flutter waves
Normal One P wave before every QRS
PR interval — grading AV block StatPearls
First-degree: constant PR > 200 ms, 1:1 conduction · Mobitz I: PR progressively lengthens, then a dropped beat · Mobitz II: constant PR with unpredictable dropped QRS · Third-degree: P waves never related to QRS (AV dissociation), escape typically < 45–50 bpm Mobitz II and third-degree block are the dangerous two — they need urgent admission and pacing, and often do not respond to atropine
Normal PR ≤ 200 ms, every P conducted
QTc interval StatPearls
Prolonged when > 450 ms (men) / > 460 ms (women); > 500 ms carries a 2–3× torsades risk Check before and during QT-prolonging drugs (antiarrhythmics, antipsychotics, antiemetics, antifungals, antimicrobials) — and correct K⁺/Mg²⁺ alongside
Normal ≤ 450 ms (men) / ≤ 460 ms (women)
Apical–radial pulse check
A pulse deficit (apical > radial) in rapid afib — weak beats never reach the wrist Measured by simultaneous apical auscultation and radial palpation — two clinicians or one very practiced one
Normal No deficit; controlled afib should also have none
Venous Thromboembolism (DVT & PE) VTE
Wells score (DVT)
Sorts pretest probability: −2 to 0 low · 1–2 moderate · 3–8 high (a simplified two-tier "likely ≥ 2 / unlikely ≤ 1" split is also in use) Points for active cancer, immobilization/casting, bedridden ≥ 3 days or major surgery within 12 weeks, deep-vein tenderness, whole-leg swelling, calf > 3 cm larger (10 cm below the tibial tuberosity), pitting edema, collateral veins, prior DVT; an equally likely alternative diagnosis subtracts 2
Normal —
D-dimer StatPearls
Elevated (≥ 500 ng/mL or 0.50 μg/mL) with active clot formation and breakdown — but an elevated result confirms nothing High sensitivity + low specificity = a rule-out test: negative in a low-probability patient excludes DVT. With high pretest probability skip it and image directly. False positives: recent surgery, trauma, pregnancy, malignancy, infection, older age
Normal < 500 ng/mL (age > 50: age × 10 ng/mL)
Duplex / compression ultrasound StatPearls
The confirmatory test of choice: a vein that fails to collapse under probe pressure is thrombosed (sensitivity ~95%, specificity ~96%) A negative first scan does not end the work-up when suspicion persists: repeat testing in 1–2 weeks can catch a propagating calf DVT (a D-dimer may suffice in selected patients). Serial compression testing raises sensitivity
Normal Complete vein collapse under direct pressure
INR (on warfarin) ASH 2020
Goal 2.0–3.0 — a lower range lets DVT risk climb; high-intensity anticoagulation (INR > 4.0) is a named bleeding risk Warfarin needs regular INR monitoring (DOACs need no routine blood monitoring); overlap parenteral heparin until the INR exceeds 2 for 24 hours (≈ 5 days)
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aPTT (on unfractionated heparin)
Goal 1.5–2 × normal Check aPTT, INR and platelet count at baseline, follow the aPTT about every 4 hours when a continuous infusion starts, and check platelets periodically for the whole course — a fall below 75,000 means suspect HIT: stop heparin, anticipate fondaparinux
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CBC, coagulation panel & chemistry
Baseline PT/INR, aPTT and platelet count before anticoagulation; polycythemia and dehydration raise blood viscosity, itself a thrombosis risk The chemistry panel checks renal function — kidney clearance differs across DOACs (≈ 80% for dabigatran vs 25% for apixaban), and UFH is used in renal failure
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Valvular Heart Disease VHD
Echocardiography (TTE first; TEE when needed)
The standard test to diagnose, grade, stage, and follow every valve lesion — leaflet morphology, gradients, valve area, chamber size, LVEF, pulmonary pressures TEE when TTE is limited (COPD, obesity, prior surgery), for prosthetic valves, for suspected endocarditis with a negative TTE, and to exclude LA thrombus before balloon commissurotomy. Surveillance in asymptomatic AS or MR: mild every 3–5 years, moderate 1–2 years, severe every 6–12 months
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AS severity on echo (Doppler) 2020 ACC/AHA guideline as reported by StatPearls
Severe = jet velocity ≥ 4.0 m/s, mean gradient ≥ 40 mm Hg, valve area ≤ 1.0 cm²; very severe = Vmax ≥ 5 m/s or mean gradient ≥ 60 mm Hg Jet velocity is the strongest predictor of symptom progression in asymptomatic patients. Asymptomatic severe AS earns valve replacement when LVEF is < 50%, an exercise test is abnormal (sustained BP drop > 20 mm Hg), progression is rapid, or BNP is > 3× normal. Exercise testing is avoided in symptomatic AS
Normal Mild: 2.0–2.9 m/s, gradient < 25 mm Hg, area > 1.5 cm² · moderate: 3.0–3.9 m/s, 25–39 mm Hg, 1.0–1.5 cm²
MS severity on echo 2020 ACC/AHA guideline as reported by StatPearls
Severe = mitral valve area ≤ 1.5 cm² (pressure half-time > 150 ms); very severe < 1.0 cm²; PA systolic pressure > 50 mm Hg or new AF adds an intervention trigger The Wilkins score (mobility, thickening, calcification, subvalvular disease; 4–16) picks the procedure: < 8 favors balloon commissurotomy, > 12 favors surgery
Normal Mitral annular area about 4–6 cm²; flow is impeded below 2 cm²
AR and MR severity on echo 2020 ACC/AHA guideline as reported by StatPearls
Severe AR: vena contracta > 0.6 cm, regurgitant fraction ≥ 50%, regurgitant volume ≥ 60 mL · severe MR: vena contracta ≥ 7 mm, EROA ≥ 0.4 cm², regurgitant fraction ≥ 50% The LV-function trigger differs by lesion: AR Stage C2 = LVEF < 50% or LVESD > 50 mm; MR Stage C2 = EF ≤ 60% — because a regurgitant LV unloads into the atrium, a 60% EF in MR already means dysfunction. Both are surgical triggers
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ECG and chest X-ray
AS: LVH, conduction delays from calcium reaching the septum · MS: broad, notched P mitrale, atrial fibrillation, later right-axis deviation · CXR: calcified valve (AS), straightened left heart border with an enlarged left atrium and pulmonary venous congestion (MS) Post-TAVR and post-surgery telemetry watches for new conduction disturbance; on an endocarditis patient a new PR prolongation or block means perivalvular abscess
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BNP / NT-proBNP 2020 ACC/AHA guideline as reported by StatPearls
Elevated with ventricular wall stress; in AS a level > 3× normal is an intervention trigger even without symptoms Released by the heart in response to pressure or stretch; supports risk stratification and heart-failure recognition, never replaces the echo
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INR (warfarin with a mechanical valve or MS + AF) 2020 ACC/AHA guideline as reported by Ryu & Tran 2022
Mechanical aortic valve without risk factors: target 2.5 (range 2.0–3.0) · mechanical mitral valve, or any mechanical valve with thromboembolic risk factors: target 3.0 (range 2.5–3.5) · MS with AF, prior embolus, or LA thrombus: about 2.5 Below range = valve thrombosis and stroke risk; above = bleeding. Bioprosthetic valves: warfarin (target 2.5) for 3–6 months during endothelialization, then daily aspirin. DOACs are contraindicated with mechanical valves and not recommended in rheumatic MS. Home INR devices are an option
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Blood cultures × 2–3 (suspected endocarditis)
Typical organism in two separate sets or persistent bacteremia = a major Modified Duke criterion (2023 update); paired with echo evidence of a mobile mass on the valve or prosthesis Draw before the first antibiotic dose, from separate sites, then repeat every 24–48 h to document clearance; add CBC, ESR/CRP, urinalysis, ECG
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Infective Endocarditis IE
Blood cultures — 3 sets, separate venipuncture sites, BEFORE antibiotics AHA 2025 blood culture-negative endocarditis statement; 2023 Duke-ISCVID (Fowler et al., Clin Infect Dis 2023)
Positive with a typical organism in 2 separate sets = a major Duke criterion; bacteremia in IE is continuous, so timing matters less than sequencing Aseptic technique, adequate volume (about 10 mL per bottle, roughly 40 mL total), one aerobic + one anaerobic bottle per set; document draw times. Pretreatment cuts yield from ~90% to 50–60% and is the leading cause of culture-negative IE. Repeat every 24–48 h until negative — the treatment clock starts at the first negative culture
Normal No growth
Echocardiography — TTE, then TEE 2023 Duke-ISCVID (Fowler et al.)
Mobile intracardiac mass on a valve or prosthetic material, abscess or pseudoaneurysm, new valvular regurgitation, or new partial dehiscence of a prosthetic valve = a major criterion TTE is the initial study (limited by COPD, prior chest surgery, obesity, prosthetic valves); TEE is recommended when TTE is negative with high suspicion, for prosthetic valves, and is more sensitive for abscess. TTE often suffices for tricuspid vegetations. Absence of a vegetation does not exclude IE — repeat after several days if suspicion persists. Embolic-risk features: vegetation > 10 mm, mobile, mitral, S. aureus
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2023 Duke-ISCVID criteria (updating the modified Duke criteria) Fowler et al., Clin Infect Dis 2023 (ISCVID living document)
Definite = 2 major, or 1 major + 3 minor, or 5 minor; possible = 1 major + 1 minor or 3 minor. Major = microbiologic (typical organism ≥ 2 sets; PCR for Coxiella, Bartonella, T. whipplei), imaging (echo or cardiac CT showing vegetation, abscess, or new regurgitation; FDG PET/CT), or IE seen at surgery Minor = predisposition (valve disease or other structural heart disease, prior IE or intracardiac devices, injection drug use), fever > 38 °C, vascular phenomena (major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, Janeway lesions), immunologic phenomena (rheumatoid factor, Osler nodes, Roth spots, glomerulonephritis), and microbiologic evidence short of major. Same arithmetic as the 2000 modified Duke criteria; 2023 added PET/CT, cardiac CT, surgical inspection, and an expanded typical-organism list, and dropped strict culture-timing rules
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ECG and continuous telemetry
Often normal — but new PR prolongation or AV block signals a perivalvular abscess extending into the conduction system (positive predictive value 88%, sensitivity only 45%) Obtain serial ECGs; a new conduction change is a surgical-consultation trigger, not a wait-and-see finding. New ST elevation is managed as a STEMI even in known IE — a coronary embolus. AV block develops in about 8% of IE
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CBC, ESR/CRP, rheumatoid factor, urinalysis, metabolic panel
Leukocytosis in acute IE; normocytic anemia of chronic disease in subacute IE; ESR/CRP elevated in about 60% (nonspecific); rheumatoid factor may be positive; urinalysis shows proteinuria, microscopic hematuria, or pyuria with glomerular injury or renal infarction Creatinine and electrolytes are the baseline for nephrotoxic regimens (gentamicin, vancomycin) in a kidney already threatened by emboli and immune complexes; on OPAT, labs are repeated weekly
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Cardiac CT and FDG PET/CT 2023 Duke-ISCVID; 2023 ESC (via Imazio 2024 summary)
Cardiac CT detects paravalvular abscess (88% sensitivity, superior to TEE); FDG PET/CT detects valve or device infection when echocardiography is inconclusive Adjuncts for diagnostic uncertainty, especially prosthetic valves and devices; both are major imaging criteria in 2023 Duke-ISCVID and 2023 ESC
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Fever-of-unknown-origin workup Petersdorf & Beeson definition (as carried by StatPearls)
Classic FUO = temperature ≥ 38.3 °C (101 °F) for at least 3 weeks without a diagnosis after a week of investigation; infections are about one-third of cases and IE — including culture-negative IE — is a common one The FUO workup itself includes three blood culture sets from different sites before antibiotics and echocardiography. Culture-negative IE prompts serology (Coxiella, Bartonella, Brucella), PCR/16S sequencing, and valve-tissue testing
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Pericarditis & Cardiac Tamponade
12-lead ECG (acute pericarditis)
Diffuse, concave ST elevation without a coronary-territory pattern + PR-segment depression, with reciprocal ST depression and PR elevation in aVR; no Q waves develop The MI trap: STEMI elevation is convex, territorial, with reciprocal depression in multiple leads and Q-wave evolution. Only 50–60% show the full four-stage sequence; ST elevation was present in about a third of one 2026 cohort, and it is often absent in uremic pericarditis. Repeat the ECG when a new effusion or hemodynamic change is suspected
Normal Isoelectric ST and PR segments
ECG in effusion / tamponade
Sinus tachycardia (most common) · low-voltage QRS · electrical alternans (beat-to-beat variation in QRS amplitude, axis or morphology) Alternans is specific but not sensitive — 17–23% of tamponade — and may precede it; new low voltage or alternans on the monitor in a patient with an effusion is a call, not a note. Continuous ECG monitoring throughout tamponade care
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Diagnostic criteria for acute pericarditis ESC 2015 (superseded by the 2025 ESC guideline)
At least 2 of 4: pericarditic chest pain · pericardial rub · new widespread ST elevation or PR depression · new or worsening pericardial effusion Elevated inflammatory markers and imaging evidence of inflammation are supporting. The 2025 ESC guideline grades the diagnosis as definite, possible or unlikely and allows for atypical presentations without classic chest pain; cardiac MRI is recommended when the diagnosis is unclear or myocarditis is suspected
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CRP and troponin (with CBC, BMP, LFTs, TSH)
CRP elevated in 96% when drawn ≥ 12 h after symptom onset; troponin elevation = myopericarditis CRP begins rising about 6 h after inflammation starts and is still normal in ~22% at presentation, so an early normal value does not clear the patient; serial CRP guides NSAID tapering and return to activity. Routine viral serology is not recommended (HIV and HCV excepted); TB testing, blood cultures and ANA are selective
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Echocardiogram ESC 2015 effusion sizes, as reported by the Italian Society of Cardiology 2024
Effusion sized by end-diastolic echo-free space — < 10 mm small · 10–20 mm moderate · > 20 mm large. Tamponade: right atrial free-wall collapse (nearly 100% sensitive and specific when it lasts > 1/3 of the cycle), right ventricular diastolic collapse, plethoric IVC > 20 mm with < 50% inspiratory collapse, mitral inflow variation > 25–30%, septal bowing, swinging heart The test of choice for effusion and the confirmation for tamponade — but tamponade is diagnosed at the bedside, and in an unstable patient the echo guides the needle rather than delaying it. Sensitivity is poor (36.8%) in the first 24 h after cardiac surgery. Order a follow-up echo before discharge after drainage
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Pulsus paradoxus (manual cuff)
Inspiratory systolic fall > 10 mmHg Inflate until all Korotkoff sounds disappear; deflate slowly and note the pressure at which sounds are heard only during expiration; keep deflating until sounds are heard throughout the respiratory cycle; the difference is the pulsus paradoxus. Also visible as respirophasic swings on an arterial-line or pulse-oximetry waveform
Normal Inspiratory fall < 10 mmHg
Chest X-ray
Enlarged cardiac silhouette; a "water bottle" heart with a large chronic effusion Compare with prior films — and remember the film can be normal in delayed post-surgical tamponade. A normal silhouette does not rule out a rapidly accumulating effusion
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High-risk predictors (admit vs. outpatient) ESC 2015 (superseded by the 2025 ESC guideline)
Major: fever > 38 °C · subacute course · effusion > 20 mm · tamponade · no NSAID response within 7 days. Minor: myopericarditis · immunosuppression · trauma · oral anticoagulation Any one predictor means admission and a search for a specific cause; about 15% of patients have at least one. Patients without predictors may be managed as outpatients
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Peripheral Arterial Disease PAD
Ankle-brachial index (ABI) — resting ACC/AHA 2024
≤ 0.90 abnormal (PAD) · 0.91–0.99 borderline · > 1.40 noncompressible (calcified arteries, result unreliable) · lower = more severe; < 0.50 is the rest-pain / tissue-loss range The cornerstone first test. Higher of the dorsalis pedis / posterior tibial systolic pressure ÷ the higher brachial pressure (use the higher arm for both legs). Patient supine (sitting raises the ABI ≈ 0.3), rest 10–30 min, no nicotine beforehand; inflate 20–30 mm Hg above the last Doppler sound. Contraindicated over a known DVT (cuff could dislodge the thrombus) and with severe leg pain, fracture, or wounds. A change of 0.15 between serial ABIs is significant. Screen those at increased risk (age ≥ 65; 50–64 with risk factors; < 50 with diabetes + 1 risk factor; atherosclerosis in another bed)
Normal 1.00–1.40
Toe-brachial index (TBI) / toe pressure with waveforms ACC/AHA 2024
≤ 0.70 abnormal Ordered when the ABI is noncompressible (> 1.40) — diabetes, CKD, advanced age stiffen the ankle arteries, but toe arteries are less affected by calcification. Also used with transcutaneous oxygen pressure and skin perfusion pressure to diagnose CLTI and predict wound healing
Normal —
Exercise (treadmill) ABI ACC/AHA 2024
A post-exercise drop ≥ 20% is abnormal — exertional ischemia For suspected symptomatic PAD with a normal or borderline resting ABI — the patient whose story says claudication but whose resting number says fine
Normal ABI rises with exercise
Doppler waveforms · segmental limb pressures · pulse volume recordings
Monophasic waveform = hemodynamically significant stenosis; biphasic = early change; pressures drop at the level of disease (thigh vs calf vs ankle) Localizes the level of disease noninvasively. In suspected ALI, a handheld continuous-wave Doppler at the bedside is the assessment — loss of the arterial signal = threatened limb; loss of arterial and venous signals = possibly irreversible
Normal Triphasic — rapid systolic upstroke, brief early-diastolic reversal, late-diastolic forward flow
Arterial duplex ultrasound ACC/AHA 2024 (surveillance)
Peak systolic velocity ratio > 2.0 ≈ ≥ 50% stenosis; > 4.0 ≈ ≥ 75% The preferred noninvasive test for bypass graft patency; surveillance ABI + duplex at 1–3 months, 6 and 12 months, then annually after vein bypass or endovascular treatment — and any time new leg symptoms appear
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CTA · MRA · digital subtraction angiography
Maps the anatomy of the stenosis or occlusion Imaging is for planning revascularization, not for diagnosis. CTA = iodinated contrast + radiation; MRA = gadolinium, no radiation; angiography is the gold standard, reserved for patients undergoing endovascular therapy
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Lipids · glucose · renal function
Risk-factor work-up, not diagnosis Cholesterol, triglycerides, and blood sugar define the targets of medical therapy; creatinine matters for contrast imaging and for the CKD-calcification trap in the ABI
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Aortic Aneurysm & Dissection AAA
Abdominal ultrasound (screening & surveillance of AAA) ACC/AHA 2022
Infrarenal aortic diameter > 3.0 cm = AAA; sensitivity 94–99%, measurements within 4 mm of CT Surveillance intervals: 3.0–3.9 cm every 3 years · men 4.0–4.9 cm / women 4.0–4.4 cm annually · men ≥ 5.0 cm / women ≥ 4.5 cm every 6 months. Bedside ultrasound cut rupture mortality 20–60% — but it is less accurate above the renal arteries and cannot reliably see a retroperitoneal bleed
Normal Infrarenal aorta < 3.0 cm (no surveillance needed)
CT / CT angiography ACC/AHA 2022
Definitive anatomy: aneurysm size and branch involvement; in dissection, the intimal flap, true and false lumen, contrast leak (rupture), and whether the ascending aorta is involved (type A vs B) First-line imaging for suspected acute aortic syndrome (Class 1) — wide availability, accuracy, and speed; sensitivity above 95%. Also the preoperative-planning scan for an AAA meeting repair criteria and the rEVAR-suitability scan in a hemodynamically stable rupture. MRA when contrast or radiation is contraindicated
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Transesophageal echo (TEE) / bedside TTE
TEE sensitivity 99%, specificity 89% — shows the flap, aortic regurgitation, pericardial effusion/tamponade, LV dysfunction TEE is preferred when the patient is hemodynamically unstable or CTA is unavailable, and intraoperatively; TTE is limited for the distal aorta but works as a first bedside look for AR and tamponade in an unstable patient
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Chest x-ray ACC/AHA 2022
Mediastinal widening (> 8 cm), loss of the aortic knob contour, "calcium sign" (intimal calcium displaced > 5 mm), tracheal or NG-tube deviation to the right, left pleural effusion Suggestive, never sufficient: up to 20% of dissections have a normal chest x-ray (sensitivity 64%). A normal film does not stop the CTA
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ECG & troponin
Often nonspecific — normal in ~31% of type A dissections; ST changes in ~8% (coronary ostium involved), with troponin mildly elevated only then The trap runs both ways: a normal ECG does not exclude dissection, and ST changes plus troponin do not prove a "simple" MI — the coronary may be dissected. Rule out dissection before anticoagulating or lysing a chest-pain patient with the wrong story
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D-dimer + Aortic Dissection Detection Risk Score (ADD-RS) ACC/AHA 2022
D-dimer > 500 ng/mL in most dissections (highly sensitive, not specific); ADD-RS scores 0–3 — one point each for a high-risk condition (Marfan/connective-tissue disease, family history, aortic valve disease, recent aortic manipulation, known TAA), high-risk pain (abrupt, severe, ripping/tearing), and high-risk exam (pulse deficit or SBP differential, focal deficit with pain, new AR murmur with pain, hypotension/shock) No biomarker is diagnostic. A low ADD-RS (0) plus a D-dimer < 500 ng/mL is the strategy that makes the diagnosis unlikely; a score of 2–3 is high risk and goes straight to CTA
Normal D-dimer < 500 ng/mL
Supporting labs (CBC, creatinine, lactate, LFTs, type & cross-match)
A falling hematocrit suggests blood loss into the wall or retroperitoneum; rising creatinine = renal ischemia; rising lactate = poor perfusion or mesenteric ischemia; elevated LFTs = mesenteric malperfusion Cross-match early — both rupture and type A repair are transfusion events. Before elective AAA repair add an echocardiogram (associated heart disease is common) and an ECG within 4 weeks of surgery (per SVS as reported by StatPearls)
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Cardiomyopathies DCM · HCM · RCM
Echocardiogram HCM thickness: ESC 2023 and AHA/ACC 2024 (via systematic review)
DCM: dilated ventricle(s), LVEF < 40%, possible mural thrombus · HCM: wall ≥ 15 mm in any LV segment (≥ 13 mm with an affected relative), SAM of the mitral valve, often EF > 65% · RCM: non-dilated, stiff ventricle · PPCM: LVEF < 45% The key test for every type — it also separates dilated from hypertrophic from restrictive. SAM has 99% specificity for HCM.
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LVOT gradient (HCM)
≥ 30 mm Hg hemodynamically significant · ≥ 50 mm Hg threshold for septal reduction, primarily if symptomatic Obstruction can appear at rest or only with exercise or provocation, because it depends on preload and afterload.
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ECG
HCM: abnormal even without obstruction — repolarization changes, prominent inferior/lateral Q waves, left atrial enlargement, left axis deviation, deep T-wave inversion · RCM: low-to-normal QRS voltage despite a thick wall suggests amyloid · Takotsubo: ST elevation → normalization → T-wave inversion → normalization, with QTc prolongation in the subacute phase In takotsubo the prolonged QTc raises the risk of torsades de pointes — continuous monitoring and avoid QT-prolonging drugs. In PPCM a QRS > 120 ms is linked to higher mortality.
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Ambulatory (Holter) monitoring AHA/ACC 2024 (reassessment interval)
Nonsustained VT in 20–30% of HCM patients Recommended for 24 to 48 hours in every patient diagnosed with HCM to assess arrhythmia and sudden-death risk; SCD risk is reassessed every 1–2 years under the 2024 US guideline.
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Cardiac MRI
Late gadolinium enhancement in over 60% of symptomatic HCM (replacement fibrosis) Extensive enhancement is one of the ICD risk factors.
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Coronary angiography
Takotsubo: no obstructive coronary disease or acute plaque rupture · DCM: rules out occult ischemic disease Takotsubo is a diagnosis of exclusion — ACS, especially STEMI, must be definitively ruled out first.
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Troponin and BNP (takotsubo, DCM)
Takotsubo: troponin rise is relatively modest (registry median ~7.7× the upper limit) while natriuretic peptides are markedly high — the discordance is a clue In DCM a low BNP helps rule out heart failure and BNP carries prognostic value; no cardiomyopathy-specific BNP cut-off is given here — see the Heart Failure page.
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Reversible-cause labs (DCM)
Thyroid function, HIV serology, electrolytes, iron studies (hemochromatosis); urine toxicology and alcohol level if substance use is suspected
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Endomyocardial biopsy (RCM)
Gold standard for cardiac amyloidosis; fat-pad aspiration positive in about 50%
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Chronic Venous Insufficiency CVI
Venous duplex ultrasound AVF/SVS/AVLS/SIR consensus (via StatPearls)
Reflux through incompetent valves — reflux "greater than 0.5 seconds" in superficial veins and "greater than 1 second in the deep veins" "Venous duplex ultrasound is the primary modality to confirm a CVI diagnosis and is considered the gold standard." The consensus relayed by StatPearls recommends the patient be upright when able to stand safely
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Ankle-brachial pressure index (ABPI) and distal pulses
Before compression: over 1 to 1.3 — apply compression · 0.8 to 1.0 — with caution · 0.6 to 0.8 — modified compression and vascular referral · under 0.5 — do not compress, urgent referral Done because "approximately 20% of patients with VLU have concurrent arterial disease." "ABPI is obtained by dividing the systolic ankle pressure by the systolic arm pressure in the supine position." An ABPI above 1.3 suggests vascular calcification and needs urgent vascular referral. If ABPI is unavailable, mild compression (20 mm Hg or less) may start after arterial disease is clinically ruled out, with a vascular assessment within 4 to 6 weeks
Normal "An ABPI greater than 1 to 1.3 is considered normal" (VLU chapter); the general ABI chapter gives "Normal: 0.9 to 1.4"
Trendelenburg test
If the leg does not refill, superficial valves are incompetent; if it refills, the valves connecting superficial and deep veins are incompetent A bedside test that "may help differentiate between CVI caused by superficial vein valves and that caused by the deep system"
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Ulcer assessment
Area, depth, edges, wound base, signs of infection, and surrounding skin changes "Tissue culture (as opposed to a swab) must be performed in fetid, purulent, or nonhealing wounds to guide antimicrobial therapy." "Unless another diagnosis is suspected, a biopsy is not warranted"
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CEAP clinical class American Venous Forum CEAP 2020 (via StatPearls)
C0 none · C1 telangiectasias · C2 varicose veins · C3 edema · C4 skin changes · C5 healed ulcer · C6 active ulcer The 2020 update added C4c (corona phlebectatica) and the modifier r for recurrent disease
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Raynaud's Phenomenon & Vasculitis Raynaud's
[RAY] Clinical history of a typical attack
Episodic color change triggered by cold or stress NIAMS: "There is no single test to diagnose Raynaud’s phenomenon. Doctors usually diagnose it based on symptoms, in particular, on a description of a typical attack upon exposure to cold."
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[RAY] Nailfold capillaroscopy
Normal in primary; abnormal capillaries suggest secondary Raynaud's "Abnormal nailfold microscopy is associated with an increased likelihood of developing a CTD, particularly scleroderma."
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[RAY] ANA and TSH
Positive ANA raises suspicion of a connective tissue disease NIAMS: "One of the more common of these tests is the antinuclear antibody (ANA) test and a thyroid stimulating hormone (TSH) test."
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[GCA][PMR] ESR and CRP
Usually markedly raised NIAMS: "These tests are measures of inflammation, but they are not specific for polymyalgia rheumatica or giant cell arteritis." StatPearls: "A normal CRP carries a high negative predictive value," but "biopsy-confirmed cases may show a normal ESR."
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[GCA] Temporal artery biopsy or color Doppler ultrasound StatPearls
Granulomatous arteritis on biopsy; halo sign on ultrasound "Patients suspected of having GCA should undergo a biopsy or color Doppler ultrasound (CDUS) of the temporal artery." "The diagnostic sensitivity of temporal artery biopsy is approximately 77%." Steroids are not delayed for either test — the ultrasound is done "upon suspecting GCA or within 1 week of beginning glucocorticoid therapy."
Normal —
[VASC] Urinalysis, renal function, chest imaging, ANCA
Hematuria and proteinuria from glomerulonephritis in ANCA vasculitis GPA and MPA can cause "hematuria, and proteinuria from a necrotizing glomerulonephritis," and lower-airway disease with "dyspnea, cough, and hemoptysis."
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Respiratory

Asthma & Status Asthmaticus
Spirometry (FEV1/FVC + bronchodilator response) StatPearls
Obstructive pattern — reduced FEV1/FVC ratio with a scooped, concave expiratory flow-volume loop. Reversibility confirms asthma: FEV1 or FVC rises > 12% and > 200 mL after bronchodilator Reversibility is the diagnostic hallmark separating asthma from fixed obstruction
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Peak expiratory flow vs personal best (zone system) NAEPP EPR-3
Green 80–100% of personal best = controlled, continue regimen · Yellow 50–80% = airways narrowing, start the action plan with bronchodilators · Red < 50% = bronchodilator immediately + emergency/clinician help Personal best is established while controlled: peak flow diary 2–4×/day for ~2 weeks; highest reading wins. Below 50%, immediate medical care is usually required
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PEF/FEV1 % predicted during an exacerbation NAEPP EPR-3
≥ 70% = mild / discharge goal · 40–69% = moderate / incomplete response · < 40% = severe — consider adjunct therapies The severity bands that drive ED escalation decisions
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ABG NAEPP EPR-3
Early: respiratory alkalosis (tachypnea blows off CO₂ → low PaCO₂). Tiring patient: PaCO₂ “normalizes,” then rises — a PaCO₂ of 40 mmHg in a distressed asthmatic indicates severe obstruction and heightened risk of respiratory failure Hypercarbia + hypoxemia = impending respiratory failure. Trend the PaCO₂, and interpret it against the patient’s work of breathing
Normal PaCO₂ 35–45 mmHg — but “normal” is NOT reassuring here
Pulse oximetry / O₂ titration target GINA 2021 executive summary · ATS 2024
Titrate oxygen to 93–95% in adults (94–98% in children 6–11) Falling pO₂ is a late finding. Pulse oximeters may miss hypoxemia in patients with darker skin
Normal —
FeNO (fractional exhaled nitric oxide) StatPearls
Exceeding 40–50 ppb can aid in confirming an asthma diagnosis An adjunct marker of airway inflammation, not a standalone diagnosis
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COPD COPD
Spirometry (post-bronchodilator) GOLD 2026
FEV1/FVC < 0.70 after a short-acting bronchodilator confirms the diagnosis — non-fully reversible obstruction. Severity by FEV1 % predicted: GOLD 1 ≥ 80% · GOLD 2 50–79% · GOLD 3 30–49% · GOLD 4 < 30% The bronchodilator-first step is the point: obstruction that fully reverses is asthma’s story, not COPD’s. GOLD also groups by exacerbation history — Group E = ≥ 2 moderate exacerbations, or ≥ 1 requiring hospitalization, in the past year
Normal FEV1/FVC ≥ 0.70
ABG StatPearls
Chronic retainer pattern: PaCO₂ > 45 mmHg (hypercapnia) with elevated HCO₃⁻ and near-normal pH — a renally compensated respiratory acidosis Draw when FEV1 < 50% predicted, SpO₂ < 95% on room air, or any clinical sign of respiratory failure. Chronic retainers may stay asymptomatic until PaCO₂ > 90 mmHg — trend against the patient’s baseline, not the textbook’s
Normal PaCO₂ ≤ 45 mmHg
Chest X-ray
Hyperinflation: flattened diaphragms, increased retrosternal air space, horizontal ribs, attenuated peripheral vascular markings, bullae The film shows the trapped air, not the obstruction — spirometry makes the diagnosis
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Blood eosinophil count GOLD 2026
≥ 300 cells/µL predicts strong ICS benefit · 100–299 modest benefit · < 100 ICS unlikely to help and pneumonia risk may outweigh benefit This single lab steers whether an inhaled corticosteroid joins the dual bronchodilator
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Alpha-1 antitrypsin level StatPearls
< 11 µmol/L (≈ < 57 mg/dL) is consistent with significant deficiency Check at least once in every COPD patient — urgently if diagnosed under 45, minimal smoking history, lower-lobe emphysema, or unexplained liver disease
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DLCO (diffusing capacity)
Reduced in emphysema — the alveolar-capillary membrane itself has been destroyed Distinguishes emphysema’s parenchymal loss from purely airway disease
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Pneumonia
Chest x-ray
New pulmonary infiltrate — infiltrates on plain film plus supporting clinical and lab features is the diagnostic gold standard The initial imaging test. CT follows if the film is inconclusive — CXR misses ~25% of aspiration infiltrates that CT sees
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Blood + sputum cultures — before antibiotics StatPearls
Obtain blood and sputum cultures in severe CAP, with blood cultures drawn before the first antibiotic dose Sequence the draw before the first dose. Low yield in mild to moderate CAP. Blood cultures are positive in < 10% of CAP; an adequate sputum sample has > 25 WBC and < 10 squamous epithelial cells per low-power field
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CURB-65 score StatPearls
1 point each: Confusion · Uremia (BUN > 20 mg/dL) · Respiratory rate ≥ 30/min · Blood pressure (SBP < 90 or DBP ≤ 60 mm Hg) · age ≥ 65. Score 0–1 → outpatient · ≥ 2 → hospital admission; higher scores prompt evaluation for ICU-level care Validated rules (CURB-65, the Pneumonia Severity Index) support site-of-care decisions but do not replace clinical judgment — CURB-65 is the bedside version to know cold
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Pulse oximetry StatPearls
< 92% indicates severe hypoxia Continuous or scheduled SpO₂ is the earliest bedside window on the V/Q mismatch worsening
Normal ≥ 95% typical on room air in healthy adults
CBC · CRP · urinary antigens
CBC with differential in every workup; elevated CRP predicts severe infection; urinary antigen testing for Legionella and S. pneumoniae in indicated patients. In HAP/VAP, leukocytosis (> 12,000/mm³) or leukopenia (< 4,000/mm³) is part of the diagnostic evidence Leukopenia and thrombocytopenia are among the signs of early deterioration (3 or more → consider ICU) — a falling WBC can be worse news than a high one
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Swallow study (VFSS / FEES)
Videofluoroscopic swallow study (modified barium swallow) or FEES is the definitive study for aspiration and dysphagia No biomarker distinguishes aspiration pneumonia from sterile pneumonitis — the swallow evaluation and the clinical course make the call
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Pulmonary Embolism PE
Wells score (pretest probability) StatPearls
Two-tier: PE likely > 4 → straight to CTPA · PE unlikely ≤ 4 → D-dimer first. Three-tier: high > 6, moderate 2–6, low < 2 Heaviest weights: clinical signs of DVT (3) and "alternative diagnosis less likely than PE" (3); HR > 100, recent immobilization/surgery, and prior VTE score 1.5 each
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D-dimer (quantitative ELISA) StatPearls
≥ 500 ng/mL is positive; < 500 ng/mL excludes PE when pretest probability is low/intermediate (sensitivity ≥ 95%) Rules out, never in — falsely elevated in pregnancy, cancer, trauma, infection, and age (specificity ~10% over 80). Age-adjusted cutoff for age > 50: age × 10 ng/mL. High pretest probability skips the D-dimer entirely
Normal < 500 ng/mL
CT pulmonary angiography (CTPA) PIOPED II
The primary diagnostic modality of choice — visualizes clot down to subsegmental arteries; sensitivity 83%, specificity 96% Needs IV contrast — check renal function and contrast allergy; a V/Q scan replaces it when CTPA is contraindicated and is the test of choice in pregnancy with a normal chest film (a normal scan excludes PE)
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ABG
Hypoxemia + respiratory alkalosis with hypocapnia early (the tachypneic patient blowing off CO₂); widened A–a gradient Acidosis is ominous — seen in massive PE with shock. Blood gases can never rule PE out
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ECG
Sinus tachycardia and nonspecific ST/T changes are the most common findings S1Q3T3 is the classic-but-unreliable finding — neither sensitive nor specific; don’t wait for it
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Troponin I / BNP ESC 2019 (via J Clin Med 2024)
Prognostic, not diagnostic — troponin is elevated in roughly 30–50% of moderate-to-large PE and flags deterioration risk; BNP tracks RV-dysfunction severity Elevated troponin plus RV dysfunction on imaging = intermediate-high risk; either one alone = intermediate-low — the intermediate-high patient earns closer monitoring for deterioration
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Tuberculosis TB
Tuberculin skin test (TST / Mantoux) CDC cutoffs (per StatPearls)
Positive at ≥ 5 mm induration — HIV, recent close contacts, prior-TB changes on x-ray, transplant & other immunosuppressed patients · ≥ 10 mm — immigrants from high-incidence countries, residents/employees of congregate settings & healthcare facilities, injection-drug users, young children, diabetes/renal failure/silicosis/malignancy, < 90% ideal body weight · ≥ 15 mm — healthy people with no risk factors 0.1 mL of 5-TU PPD given intradermally on the inner forearm — correct placement raises a 6–10 mm wheal. Read at 48–72 hours. Prior BCG vaccination can cause a lifelong false positive; testing within ~8 weeks of infection or while immunosuppressed can be falsely negative.
Normal No induration (measure induration, never redness)
IGRA blood test (QuantiFERON-TB Gold Plus, T-SPOT.TB)
Positive with TB infection — like the TST, it cannot distinguish latent from active disease A single blood draw with no return visit, and not affected by BCG vaccination — preferred for BCG-vaccinated patients and anyone unlikely to come back for a reading. False negatives with impaired immunity; ~4% indeterminate.
Normal —
Sputum AFB smear & culture
3 serial specimens, collected 8–24 hours apart, at least one early-morning — smear sensitivity only 34–80%; culture is the gold standard (sensitivity 80–93%) The nurse owns collection quality: space the specimens correctly and capture the early-morning one — overnight pooling concentrates the bacilli.
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NAAT (Xpert MTB/RIF)
Detects M. tuberculosis DNA — sensitivity ~70% on one specimen, ~90% across 3; specificity ~98% Also detects rifampin resistance (sensitivity ~96%, specificity ~98%) — an early flag for MDR-TB before cultures mature.
Normal —
Chest x-ray
Reactivation TB: patchy consolidation of the apical & posterior upper lobes, with cavitation in 20–45% of adults · primary TB: Ghon/Ranke complex, hilar lymphadenopathy, or effusion A normal film does not fully exclude TB. Every positive TST/IGRA gets a symptom review + chest x-ray to rule out active disease before it can be called latent.
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Acute Respiratory Distress Syndrome ARDS
ABG — PaO₂/FiO₂ ratio (P/F) Berlin 2012 / Global definition 2024 (Matthay et al, AJRCCM)
≤ 300 mm Hg on PEEP ≥ 5 cm H₂O defines ARDS; tiers: mild 201–300 · moderate 101–200 · severe ≤ 100 The diagnostic and staging number, drawn first. Once ventilated, the oxygenation goal is deliberately modest — PaO₂ 55–80 mm Hg / SpO₂ 88–95% — at the lowest FiO₂ that achieves it. A P/F below 150 opens the door to proning; ≤ 100 to neuromuscular blockade; below 80 to ECMO consideration
Normal > 300 mm Hg
SpO₂/FiO₂ ratio Global definition 2024 (Matthay et al, AJRCCM)
≤ 315 (valid only when SpO₂ ≤ 97%) substitutes for P/F on high-flow nasal oxygen ≥ 30 L/min, NIV, or where no ABG is available Above 97% the oxyhemoglobin curve is flat, so the ratio loses meaning. Pulse-oximeter bias matters: occult hypoxemia is up to four times more frequent in patients who identify as Black — confirm with an ABG when the number and the patient disagree
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pH and PaCO₂ ARDSNet targets as reported by StatPearls
pH goal 7.30–7.45; PaCO₂ is allowed to rise (permissive hypercapnia), with pH tolerated down to about 7.20 before bicarbonate is considered The trade for low tidal volume. Caution: hypercapnia raises pulmonary vascular resistance and right-ventricular afterload — watch hemodynamics as the CO₂ climbs
Normal pH 7.35–7.45
Chest X-ray / CT Berlin 2012 / Global definition 2024
Bilateral opacities not explained by cardiac failure or fluid overload CT helps exclude pneumothorax, pleural effusion, lymphadenopathy and barotrauma. The global definition accepts bilateral B lines and/or consolidations on lung ultrasound by a trained operator where radiography is unavailable. Heart failure looks similar on the film — the echo settles it
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Echocardiogram / LV function assessment
No left-ventricular failure to explain the edema; stages any right-ventricular dysfunction (pulmonary artery systolic pressure > 40 mm Hg with RV dilation = moderate; septal dyskinesis = cor pulmonale) Assessing LV function is crucial to separate ARDS from congestive heart failure. Noninvasive measures (echo, bioimpedance, pulse-contour analysis) are exhausted first; pulmonary artery catheters are avoided if clinically possible
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Plateau and driving pressure (ventilator) ATS 2024 (plateau); StatPearls (driving pressure)
Plateau < 30 cm H₂O (inspiratory pause); driving pressure = plateau − PEEP, kept about 13–15 cm H₂O — above 14, tidal volume drops toward 4 mL/kg High peak with normal plateau = resistance (suction, check for kinks or biting); high peak and plateau = compliance (ARDS worsening, pneumothorax, edema, mainstem intubation). A sudden rise in either is a barotrauma alarm
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Labs and cultures
CBC with differential, comprehensive metabolic panel, magnesium, ionized calcium, phosphorus, lactate, coagulation panel, troponin and cardiac enzymes; blood and sputum cultures, bronchoscopy for culture when needed The panel hunts the cause (sepsis, pneumonia) and the organ damage. Blood chemistry and fluid levels are monitored throughout; on corticosteroids add glucose (goal 140–180 mg/dL) and sodium
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Respiratory Failure & Oxygen Therapy
Arterial blood gas (ABG) StatPearls (Respiratory Failure in Adults; ABG Analysis)
Type 1: PaO₂ < 60 mmHg with normal or low PaCO₂ · Type 2: PaCO₂ > 45 mmHg with pH < 7.35 The gold standard — obtain for any deteriorating or unstable patient. Perform the modified Allen test before radial puncture (fist clenched 30 s, occlude radial and ulnar, release ulnar — the palm should re-pink in 10–15 s, or the radial stick is unsafe); use a lyophilized-heparin syringe, since liquid heparin dilutes the gas values
Normal pH 7.35–7.45 · PaCO₂ 35–45 mmHg · PaO₂ 75–100 mmHg · HCO₃ 22–26 mEq/L · SaO₂ 95–100%
HCO₃ compensation (acute vs chronic)
Acute: HCO₃ rises ~1 mEq/L per 10 mmHg PaCO₂ · Chronic: ~4 mEq/L per 10 mmHg · Acute-on-chronic: high HCO₃ and pH < 7.35 Read the gas in order: pH (acidemia < 7.35, alkalemia > 7.45) → primary component (PaCO₂ vs HCO₃) → compensation → oxygenation (PaO₂). A serum HCO₃ above 27 mEq/L is the footprint of chronic retention — about half of such patients have obesity-hypoventilation syndrome
Normal HCO₃ 22–26 mEq/L
Pulse oximetry (SpO₂) BTS / GOLD targets as carried by StatPearls and Open RN
Targets: 94–98% for acutely ill adults not at risk of CO₂ retention · 88–92% when hypercapnia is a risk (COPD, OHS, neuromuscular/chest-wall disease) · action line ≈ 90% (≈ PaO₂ 60 mmHg) Device accuracy is only 2–4%, calibrated for 70–100%. Falsely low: poor perfusion, cold extremities, hypotension, motion, dark nail polish/artificial nails, ambient light, IV dyes, severe anemia. Falsely high: carbon monoxide (standard oximeters cannot tell COHb from oxyhemoglobin). Skin pigmentation: saturation in patients with dark skin may be overestimated by about 2% (pooled 1.1%, 1.5% in Black participants across 32 studies), and occult hypoxemia below 88% was ~3× more frequent in Black than White patients — validate borderline readings against the clinical picture and an ABG
Normal 96–100% at sea level (nursing "normal" above 92–95%)
Capnography (EtCO₂) AHA (as reported by StatPearls)
Rising EtCO₂ with a normal or high waveform plateau = hypoventilation; "Capnography will diagnose hypoventilation long before the latter results in hypoxia" Measures ventilation only, not oxygenation — the right monitor for sedated or opioid-treated patients on supplemental O₂, whose SpO₂ stays normal while CO₂ climbs. A PaCO₂–EtCO₂ gap wider than 3 mmHg means increased dead space. Continuous waveform capnography is the most reliable method to confirm and monitor endotracheal-tube placement (AHA, as carried by StatPearls); a flat trace after intubation means esophageal placement
Normal 35–45 mmHg; normally within 2–3 mmHg of PaCO₂
A–a gradient
Normal gradient with hypoxemia → hypoventilation or low FiO₂ · Raised gradient → V/Q mismatch, shunt, or diffusion defect PAO₂ − PaO₂, where PAO₂ = FiO₂ × (barometric pressure − 47) − PaCO₂/0.8. A trial of FiO₂ 1.0 that fails to raise PaO₂ distinguishes true shunt from mismatch
Normal Age-dependent: roughly (age ÷ 4) + 4 mmHg
CO-oximetry (carboxyhemoglobin)
Non-smoker COHb > 3–4% abnormal · smoker > 10% suggests exposure · significant poisoning ≥ 20% (adults), ≥ 15% (children) Order when headache, nausea, dizziness, or confusion cluster in a household — the pulse oximeter reads falsely normal. A venous sample is acceptable. COHb half-life is about 320 min on room air, under 90 min on 100% O₂, about 23 min in a hyperbaric chamber. "Cherry-red" skin is a postmortem finding and must not be relied on
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Imaging & supporting labs
CXR/CT for the cause; bedside lung ultrasound for pneumothorax, effusion, consolidation, or interstitial syndrome Add CBC, CMP (including magnesium and phosphate), TSH, cultures, troponin, and ECG. In hypercapnia add spirometry, echocardiography, and polysomnography. Continuous overnight oximetry when the nurse notes snoring with pauses in breathing
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Pneumothorax & Chest Trauma PTX
Chest radiograph (upright preferred) StatPearls
Displaced visceral pleural line with a space devoid of lung markings; rim < 2 cm = small, > 2 cm = large; in tension, complete ipsilateral collapse with mediastinal shift and tracheal deviation to the opposite side First-line because it is cheap and everywhere, but it misses small pneumothoraces (upright film sensitivity ~83% for iatrogenic cases), detects only about half of isolated rib fractures, needs roughly 175 mL of pleural fluid to show a hemothorax, and can lag a pulmonary contusion by 6–48 h. An unstable patient is decompressed first and imaged after.
Normal Lung markings extend to the chest wall; no pleural line
CT chest
The gold standard when the radiograph is inconclusive — detects occult pneumothorax, hemothorax volume, rib fractures and flail segments (3D reconstruction guides surgery), and contusion earlier than plain films An occult pneumothorax seen only on CT is usually observed — a stable, asymptomatic patient may not need a chest tube. CT may be impractical in the unstable trauma patient; ultrasound and clinical exam fill the gap.
Normal —
Point-of-care ultrasound (E-FAST)
Absent lung sliding, absent B-lines/comet-tail artifact, and a lung point (diagnostic); for hemothorax it detects as little as 20 mL of pleural fluid Up to 94% sensitivity and 100% specificity in skilled hands — more sensitive than the chest radiograph, though neither sizes the pneumothorax well. Fast enough for the trauma bay.
Normal Lung sliding present with comet-tail artifact
Arterial blood gas
Hypoxemia in pulmonary contusion and flail chest; not required to diagnose pneumothorax Useful when tension physiology is suspected and to track respiratory compromise in flail chest — the degree of hypoxemia tracks the contusion’s size. Never let the ABG delay decompression.
Normal —
Ventilator peak / plateau pressures
Sudden rise in peak and plateau pressures with high-pressure alarms, desaturation, and hypotension = pneumothorax or tension until proven otherwise The ventilator is the earliest monitor of an iatrogenic tension; a pneumothorax in a patient on positive-pressure ventilation is drained, not observed.
Normal Plateau pressure kept < 30 cm H₂O with low tidal volumes
Post-insertion chest X-ray or bedside ultrasound
Tube in the pleural space with the lung re-expanding Mandatory immediately after chest-tube placement to confirm position — malposition occurs in up to 30% of insertions. A post-removal film is reviewed and reported per provider order and agency policy; emerging evidence suggests it may be unnecessary in asymptomatic patients.
Normal —
Pleural Effusion Parapneumonic effusion
Chest X-ray
Upright PA film: meniscus sign and blunted costophrenic angle once fluid typically exceeds 200 mL · lateral decubitus view detects as little as 50 mL A pre- and post-thoracentesis film is routine practice.
Normal —
Bedside ultrasound
Hypoechoic fluid; septations suggest a complex (parapneumonic or empyema) collection More sensitive than X-ray, and used to plan and guide the tap — which improves success and reduces pneumothorax risk.
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Light’s criteria (pleural fluid vs serum) Light’s criteria
Exudate if any one: fluid/serum protein > 0.5 · fluid/serum LDH > 0.6 · fluid LDH > two-thirds of the upper limit of normal serum LDH Can misclassify 25–30% of heart-failure transudates as exudates; a serum-minus-pleural albumin gradient above 1.2 g/dL or protein gradient above 2.5 g/dL in suspected heart failure points back to a transudate.
Normal Transudate: none of the three criteria met
Pleural fluid pH, glucose, LDH
In pneumonia, pH < 7.2 marks a complicated effusion that almost always needs a chest tube; glucose < 60 mg/dL and high LDH accompany it; LDH > 1000 U/L in TB, lymphoma and empyema Do not let air or local anesthetic into the pH sample — both can change the result. Send fluid for biochemistry, culture and cytology.
Normal —
Fluid appearance, cell count, triglycerides, hematocrit
Frank pus = empyema · neutrophil-predominant in parapneumonic effusion; lymphocytic in TB, malignancy, post-CABG · milky fluid with triglycerides > 110 mg/dL = chylothorax · fluid hematocrit > 0.5 × serum = hemothorax
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Pleural fluid cytology
About 60% sensitive for malignancy on the first tap; up to 90% after three samples on separate days
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Gram stain and culture
Positive = empyema, but cultures may be negative in up to 40% of fibrinopurulent effusions Streptococcus pneumoniae and Staphylococcus aureus cause about 70% of aerobic gram-positive empyema cultures.
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CT chest
Split-pleura sign — thickened, separated visceral and parietal pleura — suggests empyema
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Blood tests
CBC with differential, electrolytes, urea, creatinine, liver tests, albumin, lipase, cardiac enzymes Leukocytosis may indicate infection, bleeding or malignancy.
Normal —
Influenza & Viral Respiratory Illness Flu
Clinical diagnosis in flu season
Abrupt fever, myalgia, headache, malaise, nonproductive cough, sore throat, rhinitis Treatment does not wait for a test in high-risk patients — CDC: "Decisions about starting antiviral treatment should not wait for laboratory confirmation of influenza."
Normal —
Rapid or conventional molecular assay
Preferred test — high sensitivity and specificity; separates influenza A from B; rapid molecular results in 15–30 minutes
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Rapid antigen test
Results in about 15 minutes; high specificity but only low-to-moderate sensitivity False negatives are common — a negative rapid test does not rule flu out. A history of flu vaccination does not rule it out either.
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SARS-CoV-2 testing
Co-infection with influenza and SARS-CoV-2 can occur A positive SARS-CoV-2 result does not exclude influenza — consider both, especially in hospitalized patients with severe respiratory disease. Oseltamivir has no in-vitro activity against SARS-CoV-2.
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Chest X-ray
Obtained when there are pulmonary symptoms, to exclude bacterial pneumonia
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Pulmonary Hypertension & Cor Pulmonale PH
Right heart catheterization 2022 ESC/ERS; 6th WSPH (via StatPearls)
Pre-capillary PH: mPAP > 20 mm Hg, PAWP ≤ 15 mm Hg, PVR > 2 Wood units · post-capillary: PAWP > 15 mm Hg The gold standard that confirms the diagnosis. The most feared complication is pulmonary arterial rupture. Vasoreactivity testing is done here for idiopathic, heritable and drug-induced PAH.
Normal Pulmonary artery pressure 11–20 mm Hg (NHLBI)
Vasoreactivity test (during RHC)
Positive = mPAP falls ≥ 10 mm Hg to ≤ 40 mm Hg with unchanged or increased cardiac output Only a positive result makes a patient suitable for high-dose calcium channel blocker therapy.
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Transthoracic echocardiogram
Estimates probability: peak tricuspid regurgitant velocity > 3.4 m/s = high; 2.9–3.4 = intermediate The most important noninvasive test but only a probability estimate — it can overestimate pressure in chronic lung disease.
Normal —
ECG
P pulmonale, right axis deviation, RV strain or hypertrophy, right bundle branch block, QTc prolongation A normal ECG does not exclude PH.
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Chest X-ray and CT
X-ray: right atrial and pulmonary artery enlargement, peripheral vessel pruning · CT: pulmonary artery ≥ 30 mm, PA-to-aorta ratio > 0.9 A normal chest X-ray does not rule out PH.
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V/Q scan
A normal scan excludes CTEPH (sensitivity 90–100%, specificity 94–100%) Done in PH work-ups to rule out CTEPH — the group that may be treated surgically.
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BNP / NT-proBNP, 6-minute walk, WHO functional class 2022 ESC/ERS (via StatPearls)
The strongest survival predictors; used to place patients in low (< 5%), intermediate (5–20%) or high (> 20%) 1-year mortality risk The treatment goal is low-risk status. No BNP cut-off diagnoses PH.
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ABG and PFTs
PaO₂ low-normal or slightly low in PAH; DLCO often reduced — < 45% linked to poor outcomes An elevated PaCO₂ should raise suspicion of sleep-disordered breathing or hypoventilation.
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Screening labs
CBC, renal, liver, iron and thyroid studies; HIV, hepatitis and connective-tissue-disease tests
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Obstructive Sleep Apnea OSA
In-laboratory polysomnography (PSG) AASM scoring rules (as relayed by StatPearls)
Obstructive apneas and hypopneas with continued respiratory effort; the AHI gives severity "Nighttime in-laboratory level 1 polysomnography (PSG) is considered the gold standard for diagnosing OSA." It records EEG, pulse oximetry, nasal and oral airflow, chest and abdominal belts, ECG and EMG
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Home sleep test
Suitable for adults with a high pretest probability and no major comorbidities It can underestimate the AHI "by at least 20%," and "mild sleep apnea may go undiagnosed." A negative or inadequate home test in a high-probability patient needs in-laboratory PSG
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Apnea-hypopnea index (AHI) — severity
NHS and the Sleep Apnea Syndrome chapter: mild 5 to 14 · moderate 15 to 30 · severe over 30 events per hour The AHI is "the average number of obstructive events per hour." Diagnosis: 5 or more events per hour with symptoms or related conditions, or 15 or more regardless of symptoms. The 2025 StatPearls OSA chapter sets them slightly differently (mild 5 to 15, moderate over 15 to 30); all sources call over 30 severe
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STOP-BANG screening
Eight yes/no items — loud snoring, daytime tiredness, observed pauses, treated high blood pressure, BMI over 35, age 50 or older, neck over 40 cm, male sex Estimates "the probability of moderate-to-severe OSA": 5 or more yes answers indicate high risk, fewer than 3 low risk
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Epworth Sleepiness Scale
Score 0 to 24 "a score above 9 suggests excessive daytime sleepiness and warrants additional assessment" (StatPearls 2025; an older chapter uses greater than 10)
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Lung Cancer Bronchogenic carcinoma
Low-dose CT (screening — asymptomatic adults) USPSTF 2021 (Grade B)
Annually for ages 50–80 with ≥20 pack-years who smoke now or quit within 15 years Shared decision-making first; "If the person currently smokes, they should receive smoking cessation interventions." Harms include false positives, overdiagnosis and radiation. Not chest x-ray or sputum cytology.
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Chest x-ray → CT chest (symptoms)
Mass, hilar enlargement, effusion or collapse "Imaging should begin with a chest radiograph as the presentation of NSCLC can be nonspecific" — then CT; "radiography alone is insufficient for definitive diagnosis."
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Biopsy (bronchoscopy, needle, thoracoscopy, mediastinoscopy)
Tissue confirms type — NSCLC or SCLC "Histopathological confirmation from tissue sampling remains the diagnostic cornerstone." After a lung needle biopsy, "A chest x-ray is done after the procedure to make sure no air is leaking from the lung into the chest."
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[NSCLC] Molecular / biomarker testing (EGFR, ALK, PD-L1)
Targetable mutation or PD-L1 level guides therapy EGFR (the tumor gene) is not eGFR (kidney function).
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PET scan and brain MRI
Extent of disease; brain metastases PET "to further stage the patient"; "brain magnetic resonance imaging (MRI) is needed to assess for brain metastasis to complete the disease staging."
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CBC, electrolytes (sodium, calcium), liver and kidney function
Hyponatremia (SIADH), hypercalcemia, anemia, abnormal liver tests suggesting metastasis SIADH: "hypotonic hyponatraemia with urinary sodium in excess of 20 mmol/L" with euvolemia. In hypercalcemia, "the ionized or free calcium levels should be measured" because much serum calcium is albumin-bound.
Normal —
Pulmonary function tests
Fitness for surgery or curative radiation Candidates "should also undergo comprehensive pulmonary function testing, including spirometry and gas transfer measurements, to assess procedural fitness."
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COVID-19 Coronavirus disease 2019
Viral test — NAAT (PCR) or antigen CDC
Detects SARS-CoV-2 or its components "CDC recommends a viral test, either molecular (nucleic acid amplification test [NAAT], such as polymerase chain reaction [PCR]) or antigen tests." For high-risk patients, "use a nucleic acid amplification test (NAAT), such as a PCR test, when possible, for reliable diagnosis" to avoid treatment delay. "Do not use a serologic test that detects antibodies."
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Pulse oximetry
SpO2 ≥94% on room air = mild/moderate; below 94% or needing oxygen = severe NIH guidelines (archived 2024): "Clinicians should be aware that pulse oximeters may not accurately detect hypoxemia in people with darker skin pigmentation."
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Chest imaging
CT may show bilateral, peripheral ground-glass opacities and consolidation "A chest radiograph or computed tomography (CT) images alone are not recommended to diagnose COVID-19, but might be helpful in assessing and managing patients" (CDC).
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CBC, inflammatory markers, coagulation
Lymphopenia common; possible thrombocytopenia, high CRP, ESR and LDH; high D-dimer and fibrinogen "Lymphopenia represents a common laboratory abnormality among patients with COVID-19" (StatPearls). D-dimer and fibrinogen reflect the hypercoagulable state.
Normal —
[RDV] Before remdesivir — liver tests and prothrombin time
Baseline hepatic labs and PT VEKLURY label: "before starting VEKLURY and during treatment as clinically appropriate, perform hepatic laboratory testing. Assess prothrombin time before starting VEKLURY and monitor as clinically appropriate."
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[Long COVID] Clinical diagnosis — history and examination CDC
No laboratory test confirms or rules it out CDC (Mar. 9, 2026): "Currently, no laboratory test can be used to definitively diagnose or rule out Long COVID or to distinguish Long COVID from conditions with different etiologies." "A positive SARS-CoV-2 viral test or serologic (antibody) test is not required to establish a diagnosis of Long COVID but can help assess for current or previous infection." "Objective laboratory or imaging findings should not be used as the only measure or assessment of a patient's well-being." (Antibody tests still are not used to diagnose current COVID-19.) Clinicians document it with ICD-10-CM code U09.9, which is "not to be used in cases that still are presenting with acute COVID-19."
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Interstitial Lung Disease & Pulmonary Fibrosis ILD
Pulmonary function tests
Restrictive pattern; decreased vital capacity; diminished DLCO StatPearls: "Pulmonary function tests (PFTs) usually reveal restrictive lung function impairment, decreased functional vital capacity, and diminished carbon monoxide diffusing capacity." With coexisting emphysema, lung volumes can look relatively preserved while DLCO is "significantly decreased." NHLBI: lung function tests "which you may need every few months."
Normal —
High-resolution chest CT (HRCT) NHLBI
Scarring; in IPF, a honeycomb-like pattern NHLBI: HRCT "is used to take pictures of the inside of your lungs and look for scarring or inflammation." "For IPF, doctors look for a pattern where the lungs look similar to a honeycomb." A chest X-ray "does not provide as much detail as a high-resolution CT scan."
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IPF — a diagnosis of exclusion
Other causes ruled out first NHLBI: "Idiopathic means that your doctors cannot determine a cause of your disease at the time of diagnosis. They will rule out other medical reasons or conditions that may be causing your symptoms before diagnosing you with IPF."
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Follow-up chest CT
Fibrosis; UIP pattern in IPF; new bilateral ground-glass in an acute exacerbation "Usual interstitial pneumonia (UIP) is the histological pattern of IPF and is the most important pattern to recognize" (StatPearls). NHLBI lists chest CT "to look for lung cancer, or to see how you are responding to treatment or if your condition is getting worse."
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Exertional oxygen testing
Desaturation with activity StatPearls monitoring table: "Ambulatory desaturation testing : Every 3 to 12 months." Oxygen is recommended below 88% at rest or with exertion.
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Tissue diagnosis when needed (2022 guideline) ATS/ERS/JRS/ALAT 2022 (PMC open copy)
Transbronchial lung cryobiopsy or surgical lung biopsy ATS/ERS/JRS/ALAT 2022: "We suggest that TBLC be regarded as an acceptable alternative to SLB for making a histopathological diagnosis in patients with ILD of undetermined type in medical centers with experience performing and interpreting TBLC."
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[OFEV]/[ESB] Liver tests before and during antifibrotics
Normal baseline; watch ALT, AST, bilirubin OFEV: "Prior to treatment initiation, conduct liver function tests in all patients and a pregnancy test in females of reproductive potential." ESBRIET: "Prior to treatment, conduct liver function tests." NHLBI: "Liver function tests to monitor possible side effects from medicines."
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Prognostic markers
Worse outlook with low FVC, low DLCO, resting hypoxia, short walk distance StatPearls: "Baseline FVC less than 70% to 75% of predicted; DLCO <40% predicted; resting hypoxia (SpO2 <88%); 6MWT distance <250 m or >50m decline over 6 months."
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Cystic Fibrosis (Adult) CF
Sweat chloride test NHLBI
≥ 60 mmol/L indicates CF NHLBI: "The sweat test is the standard test for diagnosing cystic fibrosis." "A normal sweat chloride test result alone does not mean you do not have cystic fibrosis."
Normal < 30 mmol/L CF unlikely; 30–59 unclear
CFTR genetic testing
Two CF-causing mutations; modulator eligibility StatPearls: "the finding of 2 cystic fibrosis-related mutations confirms the diagnosis." NHLBI: "Your healthcare provider will first order genetic testing to figure out whether CFTR modulator therapy is likely to work for you."
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Spirometry
Low FEV1, air trapping NHLBI: "Spirometry is the most important and most widely used tool to assess lung function in cystic fibrosis." StatPearls: CF shows "air-trapping patterns with low FEV1 values proportional to the severity of the disease."
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Sputum culture
P aeruginosa, S aureus, others NHLBI: sputum culture "checks a sample of mucus for bacteria or fungi in the respiratory tract every 3 months." StatPearls: in an exacerbation "a sputum culture should be obtained, and a sensitivity profile should be obtained for the pathogens present."
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Blood sugar testing (CFRD screening) NHLBI
Starts at age 10, every year NHLBI: "Blood sugar testing checks for diabetes linked with cystic fibrosis. This testing usually starts at age 10 and happens every year."
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Liver function tests on TRIKAFTA FDA label (TRIKAFTA)
ALT, AST, alkaline phosphatase, bilirubin TRIKAFTA label: "Monitor liver function tests (ALT, AST, alkaline phosphatase, bilirubin) every month for the first 6 months of treatment, then every 3 months for the next 12 months, then at least annually."
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Other monitoring
Vitamins, liver and kidney function; stool elastase; imaging NHLBI: "Blood tests check for infection, liver and kidney function, and vitamin and mineral levels." "Pancreas function testing may include looking at an enzyme called pancreatic elastase-1 in your stool."
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Nervous

Stroke (Ischemic, Hemorrhagic & TIA) CVA
Noncontrast head CT
Obtained on arrival, before any treatment — hemorrhage must be excluded before IV alteplase, because thrombolysing a bleed worsens it The fork of the entire pathway. CT is also the gold standard for diagnosing ICH — size, edema, mass effect, intraventricular extension
Normal No acute hemorrhage
Finger-stick glucose AHA/ASA 2026
The only lab required before IV thrombolysis (unless a bleeding diathesis is suspected); < 60 mg/dL must be excluded or corrected first Hypoglycemia mimics stroke and is a thrombolysis exclusion. In acute stroke, keep glucose 140–180 mg/dL and never below 60
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NIHSS
The standard targeted neuro exam — baseline severity and serial monitoring: consciousness, language, dysarthria, motor, visual fields, gaze, facial palsy, ataxia. 15 items, maximum score 42 Usable by trained providers who are not neurologists. A rising score on serial checks is deterioration — escalate immediately
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MRI with DWI + vessel imaging (TIA workup)
Brain MRI with diffusion weighting within 24 h preferred (CT/CTA/CTP if MRI contraindicated); urgent CTA/MRA from aortic arch to vertex Plus labs: CBC, ESR, coagulation, metabolic panel, lipids, fasting glucose, HbA1c — the TIA is worked up as the warning it is
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ECG + prolonged rhythm monitoring
ECG, TTE/TEE, and Holter or prolonged monitoring — primarily to find paroxysmal atrial fibrillation, the hidden cardioembolic source Finding afib changes prevention from antiplatelets to anticoagulation — the monitor is looking for the reason the clot formed
Normal —
CTA "spot sign" (hemorrhagic)
Contrast extravasation into the hematoma = ongoing bleeding, associated with fatality A spot-sign-positive patient is still actively bleeding — expect maximal BP control and surgical evaluation
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Increased ICP & Traumatic Brain Injury ICP
ICP monitoring (external ventricular drain) BTF 4th ed.
Elevated — treat above 22 mmHg in severe TBI; 20–25 mmHg is the generic pathological band The EVD is the gold-standard monitor and a treatment (CSF drainage). Zero the transducer at the foramen of Monro — externally, the tragus of the ear; releveling after every position change keeps the number honest
Normal 7–15 mmHg (supine adult)
Cerebral perfusion pressure (calculated) BTF 4th ed.
Target 60–70 mmHg — computed as MAP − ICP at the bedside Both levers matter: a falling CPP is fixed by lowering ICP or raising MAP (fluids, vasopressors) — never by accepting hypotension
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Noncontrast head CT
Biconvex hyperdense mass = epidural · crescent collection = subdural · midline shift, edema, fractures The initial imaging gold standard in TBI. Lumbar puncture is contraindicated with midline shift or obstructive hydrocephalus — the sudden pressure change can trigger herniation
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Glasgow Coma Scale (serial) StatPearls (GCS)
Mild TBI 13–15 · moderate 9–12 · severe 3–8; GCS ≤ 8 = comatose → intubate Trend it: a drop of ≥ 2 points is report-now. Intubated patients score “V-ET” (a pseudoscore); sedatives — benzodiazepines especially — depress the score and confound the exam
Normal 15 (E4 V5 M6)
ICP waveform
P2 rising above P1 = falling brain compliance — the buffer is running out A normal ICP number with an abnormal waveform still means trouble is close
Normal P1 > P2 > P3
Serum osmolality (on mannitol)
Checked every 4–6 h — hold/discontinue mannitol at ≥ 320 mOsm With sodium, potassium, renal function, urine output, and volume status: osmotherapy dehydrates the whole patient, not just the brain
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Seizure Disorders & Status Epilepticus
EEG StatPearls
Focal or generalized epileptiform discharges — the EEG hallmark of seizure activity Stat EEG when a paralyzed/intubated patient may still be seizing; EEG is mandatory to diagnose nonconvulsive status epilepticus. Video monitoring with EEG helps determine the nature of the seizures and rule out look-alikes; to find where focal seizures start — for example when surgery is considered — NINDS describes electrodes implanted in the brain (SEEG), MEG, PET and SPECT
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EEG in absence epilepsy StatPearls
Bilaterally synchronous, symmetric 3-Hz spike-and-wave discharges Hyperventilation (~2 minutes of repetitive blowing) can provoke an episode during the recording — a bedside provocation test
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Finger-stick glucose
Checked immediately in the actively seizing patient — hypoglycemia is a rapidly reversible provoked cause Treat hypoglycemia when found; give thiamine before dextrose if deficiency is suspected
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Serum glucose, electrolytes (especially sodium), CBC, toxicology screen
The provoked-cause hunt: hypoglycemia, hyponatremia, hypocalcemia, and drug toxicity are all seizure precipitants Add a pregnancy test in women of childbearing age
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Anticonvulsant drug levels
Often subtherapeutic — about two-thirds of patients with levels drawn were below range Nonadherence and missed doses are among the most common causes of breakthrough seizures — draw the level before assuming the drug failed
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Neuroimaging (CT/MRI)
Ordered to rule out causes of the seizure and/or confirm epilepsy — CT or MRI (SPECT/PET in selected cases) alongside the EEG; in status epilepticus a head CT is appropriate in most situations MRI/CT (with PET-SPECT in selected cases) round out the epilepsy workup
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Meningitis & Encephalitis
Lumbar puncture — opening pressure & appearance StatPearls
Bacterial: elevated pressure, turbid (cloudy) CSF · Viral: normal pressure, clear CSF The diagnostic gold standard — measure opening pressure whenever possible. CT first only when herniation-risk features are present (GCS < 10, new seizures within a week, focal deficits, papilledema, severe immunocompromise, prior CNS disease, comorbidities in adults > 60); otherwise CT only delays therapy
Normal 90–180 mm H₂O · clear, colorless
CSF WBC & differential StatPearls
Bacterial: > 1,000–2,000/µL, neutrophil predominance · Viral: < 300/µL, lymphocytic predominance The cell type is the fork: neutrophils say bacterial, lymphocytes say viral. Aseptic meningitis = pleocytosis (> 5 cells/mm³) with negative bacterial cultures
Normal < 8 cells/µL
CSF protein StatPearls
Bacterial: > 200 mg/dL · Viral: < 200 mg/dL (normal or mildly elevated) Leaky, inflamed vessels let protein flood in — the more purulent the process, the higher it climbs
Normal 15–45 mg/dL (lab-dependent)
CSF glucose StatPearls
Bacterial: < 40 mg/dL — glucose goes DOWN · Viral: normal The highest-yield single value on the table. The CSF-to-serum glucose ratio is more reliable than the absolute number — always compare against a serum glucose
Normal 50–80 mg/dL
Blood cultures ×2 StatPearls
Positive in ~53% of bacterial meningitis (concurrent bacteremia) Draw before the first antibiotic dose — they may name the organism even when the LP is delayed. Never let any test delay the antibiotics themselves
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Encephalitis workup: CSF PCR · MRI · EEG StatPearls
HSV PCR 96% sensitive, 99% specific (the HSV-encephalitis gold standard) · MRI > 90% sensitive for temporal-lobe changes · EEG: lateralizing periodic sharp-and-slow complexes in ~two-thirds PCR also identifies enterovirus and VZV in aseptic meningitis; CSF lactate helps separate bacterial from aseptic disease. HSE figures are StatPearls-sourced
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Spinal Cord Injury SCI
Noncontrast CT StatPearls
The primary imaging modality — sensitivity > 98% for cervical spine injuries Fast and first; it finds the fractures and dislocations
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MRI
More reliable than CT for soft-tissue and cord pathology — what the cord itself looks like The follow-on study when the deficit needs explaining beyond the bones
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ASIA (ISNCSCI) examination ASIA
Sensory + motor levels and sacral sparing at S4–S5 (deep anal pressure, voluntary anal contraction) → grade A (complete) through E (normal) Serial exams are the point — they track ascent or improvement shift by shift
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MAP (arterial pressure monitoring) 2024 guideline (per StatPearls)
Augment to a minimum 75–80 mm Hg, avoid actively pushing beyond 90–95 mm Hg, maintain 3–7 days Perfusion defense against the ongoing secondary injury; fluids first, then norepinephrine as the preferred pressor
Normal Classic convention: MAP 85–90 mm Hg × ~7 days — still widely taught
Neurogenic shock parameters StatPearls
SBP < 90 mm Hg with HR < 80 bpm — hypotension that cannot mount a tachycardia Can persist up to 4–5 weeks; warm pink skin separates it from hypovolemia
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AD episode (BP against baseline) StatPearls / MSKTC
SBP ≥ 20 mm Hg above the patient’s baseline; a significant episode typically SBP ≥ 150; pressures can reach 300 mm Hg Know the patient’s baseline — a "normal-looking" BP can already be dysreflexia. Check BP every 5 minutes during an episode
Normal Baseline BP in high SCI runs low
Parkinson’s Disease PD
Clinical examination — MDS 2015 diagnostic criteria MDS 2015 criteria (as reported by Munhoz 2024 and the DGN 2023 guideline)
Parkinsonism = bradykinesia plus at least one of rest tremor or rigidity; then "clinically established" (no absolute exclusions, ≥ 2 supportive criteria, no red flags) or "clinically probable" (red flags allowed if counterbalanced 1:1 by supportive criteria) No lab or imaging study confirms PD — the diagnosis is clinical. Postural instability is not part of the MDS definition of parkinsonism. Supportive criteria: clear dopaminergic response, levodopa-induced dyskinesia, documented rest tremor, olfactory loss. Absolute exclusions include dopamine-antagonist exposure and normal presynaptic dopaminergic imaging. Red flags for atypical disease: recurrent falls (> 1/yr) within 3 years, early severe dysphagia, symmetric onset, wheelchair within 5 years. Observing the course for more than 5 years raises diagnostic accuracy from 53% to over 85%
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Response to levodopa DGN 2023 guideline (Hopfner et al., J Neurol 2024)
A sustained, dramatic improvement (> 70%) over months of therapy is a supportive criterion; no response despite moderate severity is an absolute exclusion Acute levodopa and apomorphine tests "should not be performed routinely" to diagnose PD, although a marked acute response (UPDRS III > 30%) counts as a supportive criterion; accuracy improves with long-term follow-up by an expert
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DaTscan (¹²³I-FP-CIT SPECT) DGN 2023 guideline; StatPearls
Reduced striatal dopamine-transporter uptake in PD; symmetric, normal uptake in drug-induced parkinsonism and essential tremor Not a routine test — "its routine use is discouraged" — but it "may be performed early in the disease course to detect nigrostriatal deficits in cases where the diagnosis of Parkinson or tremor syndromes is unclear." Its nursing value is the drug-induced contrast — a normal scan in a rigid patient points back to the MAR
Normal Symmetric striatal uptake
MRI brain DGN 2023 guideline; StatPearls
Normal in PD — used to exclude other parkinsonian syndromes (normal-pressure hydrocephalus, stroke, mass) MRI "can exclude other causes of parkinsonism, such as tumors, NPH, or cerebrovascular accidents," and the DGN recommends cranial MRI early "to aid in the differential diagnosis of Parkinson syndromes" — it does not confirm PD itself
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Hoehn & Yahr stage
1 unilateral, minimal disability · 2 bilateral or midline, balance intact · 3 bilateral with impaired postural reflexes, still independent · 4 severely disabling, still walks/stands unassisted · 5 wheelchair- or bed-bound unless aided Stage 3 is the fall-risk hinge — postural reflexes fail. Severe non-motor symptoms are about 6× more likely at stage 3 and about 28× at stages 4–5 than at stages 1–2. The MDS-UPDRS quantifies mentation, mood, ADLs, tremor, motor exam, and complications for longitudinal tracking
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Orthostatic vital signs StatPearls: Autonomic Dysfunction
Systolic fall ≥ 20 mmHg or diastolic ≥ 10 mmHg within 3 minutes of standing (≥ 30 systolic if supine hypertension coexists) Measure BP and HR supine and after 3 minutes standing — at admission, after any dopaminergic dose change, and before first ambulation. When positive, review the medication list — antihypertensives, antidepressants, and antiparkinsonian agents are listed causes, and the first non-drug step is to "Discontinue exacerbating medications"
Normal Drop < 20/10 mmHg on standing
Labs — CK and WBC when withdrawal syndrome is suspected; monitoring on levodopa
No lab diagnoses PD. In parkinsonism-hyperpyrexia syndrome: CK markedly elevated ("can be profound") and WBC 10,000–40,000/mm³ with a left shift On levodopa, expect periodic BUN/creatinine, hepatic function, and vitamin B12 / methylmalonic acid (levodopa-associated neuropathy). In a patient who is falling, B12, thyroid function, and vitamin D are part of the work-up
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Swallow evaluation
Bedside screen may show cough, wet voice, or delayed swallow — but the bedside exam misses more than 50% of significant aspiration Videofluoroscopic swallow study or fiberoptic endoscopic evaluation (VFSS/FEES) is the gold standard. Request the speech-language evaluation before oral intake whenever dysphagia is suspected; a gastrostomy may be indicated when conservative measures fail
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Alzheimer’s, Delirium & Dementia
Confusion Assessment Method (CAM) CAM (via StatPearls)
Positive = (1) acute change with fluctuating course and (2) inattention, plus either (3) disorganized thinking or (4) altered level of consciousness Sensitivity 94–100%, specificity 90–95% — its high specificity lets it rule delirium in; the 3-minute 3D-CAM performs similarly. Needs a baseline from family or caregiver to judge "acute change." Adaptations exist for the ICU, ED and nursing home
Normal Features 1 and 2 absent
CAM-ICU (with RASS first) CAM-ICU / ICDSC (via StatPearls)
Step 1: Richmond Agitation-Sedation Scale (−5 to +4) — patient must be arousable enough to assess; step 2: the four CAM features, 3 of 4 required (1 and 2 plus 3 or 4) Alternative ICDSC: consciousness rated A–E, then 8 items, score ≥ 4 = delirium. Both screens run every shift in the ICU as the "D" of the ABCDEF bundle
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4AT (4 A’s Test) 4AT (via StatPearls / PMC validation)
0 = delirium/cognitive impairment unlikely · 1–3 = possible cognitive impairment · ≥ 4 = possible delirium Under 2 minutes, no special training: Alertness, AMT-4 (age, date of birth, place, current year), Attention (months of the year backward from December), Acute change or fluctuating course. Pooled sensitivity 76%, specificity 94%
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Delirium work-up — first rule out the killers
Hypoxia (SpO₂/ABG), MI (ECG), hypoglycemia (glucose) first; then CBC, complete metabolic panel, urinalysis, ECG, chest radiograph, bladder scan for retention; blood cultures, toxicology, EEG, LP only when indicated Brain imaging is not routine — reserve CT for a new focal deficit, fall or head trauma, unexplained depressed consciousness, or suspected intracranial infection or bleed (focal deficits, not anticoagulation status, predict an abnormal scan). Pain and constipation are assessed as part of the work-up
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Urinalysis in the confused older adult McGeer criteria / AGS Choosing Wisely 2013
True UTI pattern: > 10 WBC/hpf, positive nitrite ± leukocyte esterase, culture typically ≥ 100,000 CFU/mL — with fever, dysuria, suprapubic pain, or new urgency, frequency or incontinence The trap: asymptomatic bacteriuria is present in 40–50% of adults over 80 and about half of long-term-care residents. Bacteriuria plus confusion is not proof — AGS Choosing Wisely: "Don’t use antimicrobials to treat bacteriuria in older adults unless specific urinary tract symptoms are present"
Normal ≤ 10 WBC/hpf, nitrite negative
Cognitive screening (MMSE · MoCA · Mini-Cog)
Documents the domain pattern and decline over time; MMSE is a 30-point, under-10-minute test of orientation, registration, attention, recall and language; MoCA is more sensitive for MCI and executive function; Mini-Cog is 3-item recall plus clock drawing in about 3 minutes A screen alone never diagnoses dementia — functional decline is required, and neuropsychological testing is the most reliable way to detect MCI. Nurses repeat the same tool over time to establish baseline and catch decline
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Dementia laboratory screen
CBC, urinalysis, metabolic panel, vitamin B12, folate, TSH, syphilis and HIV serology — normal in AD; the purpose is to catch the reversible mimics Also screen for delirium, depression, offending medications, alcohol, sleep apnea and sensory deficits before labeling anyone "demented." Routine labs reveal no specific abnormality in AD
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Neuroimaging & AD biomarkers
MRI without contrast is often the initial test: entorhinal → medial temporal/hippocampal atrophy in AD; FLAIR white-matter ischemia and lacunes with a preserved hippocampus in vascular dementia. CSF: Aβ42 decreased, p-tau and total tau increased; amyloid PET confirms plaque pathology Amyloid confirmation (PET or CSF) is the gate for anti-amyloid antibody therapy; DaTscan separates Lewy body/parkinsonian dementias. Blood p-tau tests are not yet ready for routine use, and the definitive diagnosis remains pathological — clinical history gives a probable diagnosis
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Multiple Sclerosis MS
MRI brain & spinal cord with gadolinium 2024 McDonald criteria (Solomon et al., Neurology 2026)
T2-hyperintense lesions (T1 iso/hypointense "black holes") with a periventricular predilection, Dawson fingers perpendicular to the ventricles, and gadolinium enhancement where the blood-brain barrier is actively broken The diagnosis rests on dissemination in space — lesions in at least 2 of 5 typical sites (periventricular, cortical/juxtacortical, infratentorial, spinal cord, and, new in 2024, optic nerve; the 2017 revision used four) — and dissemination in time: new T2 lesions on follow-up, enhancing plus non-enhancing lesions on one scan, or a second clinical attack. In 2024, DIT is no longer required for every patient; lesions in 4 of 5 sites, positive CSF, a central-vein sign, or a paramagnetic rim lesion can substitute. Cord lesions in MS are short and focal; a lesion spanning 3 or more segments points to NMOSD
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CSF oligoclonal bands (lumbar puncture) 2024 McDonald criteria
≥ 2 CSF-restricted bands (present in CSF, absent in blood) = positive CSF; alternatively an intrathecal kappa free-light-chain index ≥ 6.1 Positive CSF has counted as proof of dissemination in time since 2017. Bands are not specific — raised CSF IgG can also reflect a CNS infection or another inflammatory or autoimmune disease (the MS differential includes Lyme disease and HIV), which is why positive bands never diagnose MS alone. Classic MS CSF: elevated protein and myelin basic protein, a few mononuclear cells, raised IgG
Normal Fewer than 2 CSF-restricted bands
CSF IgG index
Elevated — intrathecal antibody production Often ordered with the bands, but a CSF IgG test alone cannot diagnose MS; a high index may equally mean infection or another inflammatory or autoimmune CNS condition
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Visual, brainstem & somatosensory evoked potentials
Slowed conduction in pathways the patient has never noticed — subclinical involvement Supportive only: evoked potentials were dropped from the McDonald criteria and cannot establish dissemination. Teach them as evidence of slowed conduction, not as a diagnostic test
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AQP4-IgG & MOG-IgG serum antibodies
Negative in MS; positive AQP4-IgG (60–90% of NMOSD) redirects the diagnosis Ordered when features are atypical — bilateral or posterior optic neuritis, a long cord lesion, unexplained hiccups, nausea, or vomiting (area postrema syndrome). Getting this right matters because natalizumab, beta-interferon, and fingolimod can worsen NMOSD; misdiagnosis of MS runs about 15% at subspecialty centers
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Relapse work-up: CBC, electrolytes, urinalysis ± culture
Normal in a true relapse; leukocytes, nitrites, and bacteria on urinalysis (with or without fever) unmask a UTI-driven pseudo-relapse Drawn before any relapse is labeled: a relapse is defined in the absence of fever or infection. White-cell casts suggest renal involvement; in a catheterized patient the culture threshold is 1,000 CFU/mL (IDSA definition as carried by StatPearls). Misdiagnosis here leads to inappropriate steroids or DMT changes
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Post-void residual (bladder scan) ± urodynamics
Elevated residual with incomplete emptying; sustained bladder pressures > 40 cm H₂O on urodynamics threaten the upper urinary tract Reviewed periodically — and re-checked after starting anticholinergics, because people with MS are the most likely to develop retention on them
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Myasthenia Gravis MG
Serum antibodies — anti-AChR, then anti-MuSK, then anti-LRP4 / cell-based assay StatPearls
Anti-AChR positive in ~80–85% of generalized and ~50% of ocular MG; if negative → anti-MuSK (5–10%); if both negative → anti-LRP4 or a cell-based assay First-line and specific — a positive result confirms MG. A negative standard assay does not exclude it (seronegative MG); anti-striational antibodies (about 30%) flag possible thymoma
Normal Undetectable
Repetitive nerve stimulation (RNS) StatPearls
Decrement > 10% in compound muscle action potential amplitude between the first and fourth or fifth response at slow-rate (2–5 Hz) stimulation Hold anticholinesterase drugs for at least 12 hours before the study or the result is falsely normal; limb warmed to 35 °C; most sensitive in facial muscles. Lambert-Eaton shows the opposite — an incremental response (≥ 100%) with fast-rate stimulation
Normal No significant decrement
Single-fiber EMG (SFEMG) StatPearls
Increased jitter — impaired neuromuscular transmission The most sensitive diagnostic test for MG, but abnormal jitter is not specific to MG
Normal Normal jitter
Ice-pack test (bedside, ptosis only) Marinos et al. 2018 (Eye)
≥ 2 mm improvement in ptosis after ice is held over the closed eye for 2–5 minutes = positive Cooling lowers acetylcholinesterase activity, so ACh persists longer at the junction. Specificity ~97% but sensitivity as low as 38.5% on a single test (73% with repetition) — a positive test is convincing, a negative excludes nothing; it cannot assess the extraocular muscles and is not the primary diagnostic approach
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Edrophonium (Tensilon) test — the historical exam answer FDA discontinuation 2018 (as reported by Keritam et al. 2026)
A short-acting IV anticholinesterase transiently improved strength in MG (historical sensitivity 71–95%) Obsolete in the US: edrophonium was discontinued by the FDA in 2018 over safety and false-positive concerns, and guidelines say it should not be the primary diagnostic approach. It has been replaced by antibody testing and electrodiagnostics — and it is not how myasthenic and cholinergic crises are told apart today
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Chest CT (or MRI) — thymoma screen StatPearls; International Consensus Guidance 2016
Mandatory in every newly diagnosed patient; thymic hyperplasia or thymoma A thymoma changes management (all thymomas are resected). Purely ocular disease also gets brain/orbit MRI to exclude a structural mimic. In pregnancy, non-contrast CT is safe but is preferably postponed until after delivery
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Bedside forced vital capacity (FVC) and negative inspiratory force (NIF) StatPearls Guillain-Barré chapter (neuromuscular criteria); Gilhus 2023 (J Neurol)
Neuromuscular respiratory-failure criteria (the "20/30/40 rule"): "Vital lung capacity <20 mL/kg, or a maximal inspiratory pressure <30 cm H2O, or a maximal expiratory pressure <40 cm H2O" Measure serially — trend beats snapshot. In MG, vital capacity "correlates less well to the need of mechanical ventilation than in other neuromuscular disorders," so bulbar decline, accessory-muscle use and a weak cough weigh as much as the number. The 20/30/40 rule comes from the Guillain-Barré/neuromuscular literature; no MG guideline sets these thresholds
Normal Adult vital capacity about 3–5 L
Arterial blood gas StatPearls Guillain-Barré chapter (neuromuscular criteria)
The neuromuscular intubation criteria carried by the Guillain-Barré literature list PaCO₂ > 48 mm Hg or PaO₂ < 56 mm Hg — not MG-specific thresholds The intubation decision is made on bedside strength and the FVC/NIF trend, not the gas — by the time PaCO₂ rises, those criteria have usually already been met, so a normal reading is not reassurance. Also at diagnosis: ANA, rheumatoid factor, thyroid function (autoimmune comorbidity), and CBC/LFTs before azathioprine
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Guillain-Barré Syndrome GBS
Clinical criteria (NINDS / Brighton Collaboration) NINDS / Brighton Collaboration (per Leonhard et al. 2019)
Required: progressive bilateral weakness of arms and legs plus absent or decreased tendon reflexes in the affected limbs, with progression not beyond 4 weeks The diagnosis is clinical — CSF and nerve conduction studies support it but are not required, and treatment is never delayed for them. Brighton criteria grade certainty in 4 levels
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Cerebrospinal fluid — albuminocytologic dissociation EAN/PNS 2023 cell-count thresholds (via Freiha 2026 / Wiegers 2025)
Elevated protein with a normal cell count — WBC typically ≤ 5/µL; protein can climb into the hundreds (reported up to 1,800 mg/dL) The timing trap: protein is normal in about half of patients in the first week and rises in 70–90% by the end of the second — a normal early LP does not exclude GBS. Cells 5–50/µL are compatible but should prompt thought; > 50/µL means look for another diagnosis. After the tap, the provider may have the patient lie flat for 1–2 h to prevent headache
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Nerve conduction studies / EMG
Reduced conduction velocities, temporal dispersion, partial motor conduction block, prolonged or absent F-waves and H-reflexes; the sural-sparing pattern (sural sensory response normal while median/ulnar are abnormal) Absent H-reflexes are 95–100% sensitive and sural sparing 91–98% specific — but early studies may be normal within the first week (sensitivity as low as 22% in early AIDP, 87% by week 5); repeat at 2–3 weeks. Used to support the diagnosis, no longer to gate treatment by subtype
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Bedside respiratory measurements — VC/FVC, MIP (NIF), MEP, single-breath count
At risk — the 20/30/40 rule: VC < 20 mL/kg, MIP weaker than −30 cmH₂O, or MEP < 40 cmH₂O. VC < 15 mL/kg (or < 1 L) → elective intubation. Single-breath count ≤ 19 predicts ventilation; cannot reach 15 = impending failure These are the nurse’s serial tests — frequency is individualized to the rate of deterioration, autonomic status and phase of illness, not a fixed schedule. Sign convention: a NIF of −25 is worse than −35 (the patient cannot pull as negative). Never substitute SpO₂ — it falls last. Meeting 20/30/40 = ICU-level risk; intubate on trend plus clinical signs, electively
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EGRIS (Erasmus GBS Respiratory Insufficiency Score) Erasmus GBS Respiratory Insufficiency Score (per Leonhard et al. 2019)
Probability of ventilation within 1 week: 0–2 low (4%) · 3–4 intermediate (24%) · ≥ 5 high (65%) Points: days from onset to admission > 7 = 0, 4–7 = 1, ≤ 3 = 2 · facial and/or bulbar weakness absent = 0, present = 1 · MRC sum score 60–51 = 0, 50–41 = 1, 40–31 = 2, 30–21 = 3, ≤ 20 = 4. Derived in a Dutch population and not yet validated internationally — a triage aid, not a gate
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MRC sum score & GBS disability scale
Lower = weaker: sum of 0–5 grades for bilateral shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, ankle dorsiflexion (max 60 = normal). Immunotherapy is indicated when the patient cannot walk 10 m independently (GBS disability score ≥ 3) Serial strength grading of neck, arms and legs plus reflexes is the neuro assessment — the trend, not one value, drives escalation. Inability to lift the arms 1 week after intubation or to flex the foot predicts prolonged ventilation
Normal MRC sum 60
Arterial blood gas / SpO₂
Normal until late. PaCO₂ > 48 mm Hg or PaO₂ < 56 mm Hg are ICU/intubation criteria — by then the pump has already failed A late indicator only. Continuous cardiac telemetry and blood-pressure monitoring run alongside because dysautonomia deepens with respiratory failure
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Anti-ganglioside antibodies & pre-treatment labs
Not recommended routinely — a negative result does not rule out GBS. Exception: anti-GQ1b is positive in up to 90% of Miller Fisher syndrome Do not wait for antibody results to start treatment. Before IVIG: check IgA (anaphylaxis risk in IgA deficiency). All patients: watch sodium (hyponatremia is a listed complication). Spinal MRI is used mainly to exclude cord compression or myelitis
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Migraine & Headache Disorders Migraine
Clinical diagnosis
History, examination and the international criteria (restated above) — no test confirms migraine MRI and CT are not usually used to diagnose migraine; EEG and CSF analysis are not routine.
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Headache diary
After each headache: time of day, intensity and duration, light/smell/sound sensitivity, activity just before, all medicines taken (prescription and OTC); menstrual days Identifies personal triggers and exposes medication-overuse patterns.
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Neuroimaging — when indicated
Acute severe first or worst headache (exclude SAH), new headache at 50 or older or immunosuppressed, headache over 72 hours, headache waking from sleep
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Noncontrast head CT (thunderclap)
Looks for subarachnoid hemorrhage; within 6 hours of onset with the Ottawa SAH rule, 95% sensitive and 100% specific If negative and suspicion is high, lumbar puncture follows — always after imaging.
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Medication history (MOH screen)
Headache 15+ days/month with acute medicines on 10–15+ days/month for over 3 months 90% of patients with MOH use several different medicines.
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Amyotrophic Lateral Sclerosis ALS
Clinical diagnosis over time
Progressive UMN and LMN signs in more than one region, with mimics excluded "There is no single test that can definitely diagnose ALS." Tests "should be performed at regular intervals to assess whether symptoms are getting worse over time." El Escorial and Awaji criteria appear as relayed by StatPearls
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Electromyography and nerve conduction studies
Acute denervation (fibrillations, positive sharp waves), chronic denervation and reinnervation (large motor unit potentials) "EMG contributes to the diagnosis in up to 90% of cases"
Normal Sensory action potentials normal
MRI of the brain and spine
"MRI will typically be normal with ALS" Done "primarily to exclude other potential causes of the patient’s symptoms." Blood and urine tests, lumbar puncture and muscle biopsy may also exclude mimics
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Genetic testing
SOD1 or C9ORF72 mutation in some patients "genetic testing is encouraged upon diagnosis, particularly for the SOD1 and C9ORF72 genotypes" — a SOD1 mutation makes tofersen an option
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Pulmonary function — vital capacity, SNIP, pCO2, overnight oximetry
Falling VC; NIV considered at VC under 50%, SNIP under 40 cm H2O, pCO2 over 45 mm Hg, or significant overnight desaturation (StatPearls) "Pulmonary function tests are done every three months." The Motor Neuron Disease chapter lists vital capacity under 80% among NIV indications — thresholds differ between sources
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Bell’s Palsy & Trigeminal Neuralgia Bell’s palsy (CN VII, idiopathic facial palsy)
[Bell’s palsy] Clinical exam — upper and lower face
Whole half-face weak, including forehead, eyelid and mouth "There is no specific laboratory test to confirm diagnosis of Bell’s palsy." It is a diagnosis of exclusion; imaging if there is "a gradual progression of facial weakness or if more than facial expression, taste, and hearing sensitivity are affected."
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[Bell’s palsy] Severity grading
House-Brackmann scale (grades I–VI) Electromyography and nerve conduction studies "may help determine how serious the disorder is and the chances of recovery."
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[Bell’s palsy] Lyme and viral testing
When exposure or rash suggests another cause "Laboratory tests for Lyme disease and other viruses may be considered to aid in diagnosis."
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[Trigeminal neuralgia] MRI (± MRA)
Vessel compressing the nerve root; excludes MS plaque or tumor "The physical examination of patients with trigeminal neuralgia does not regularly reveal a focal neurologic deficit." A dental exam rules out tooth pain.
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[Carbamazepine] Baseline CBC with platelets, liver function; HLA-B*1502 in at-risk ancestry FDA label (Tegretol)
Normal before starting "COMPLETE PRETREATMENT HEMATOLOGICAL TESTING SHOULD BE OBTAINED AS A BASELINE." HLA-B*1502 screening for "PATIENTS WITH ANCESTRY IN GENETICALLY AT-RISK POPULATIONS."
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[Carbamazepine] Serum sodium FDA label (Tegretol)
Watch for hyponatremia (SIADH) "Elderly patients and patients treated with diuretics are at greater risk of developing hyponatremia."
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Subarachnoid Hemorrhage & Cerebral Aneurysm SAH
Noncontrast head CT
Blood in the subarachnoid space The first test. Sensitivity is highest within about 6 hours and falls over days (StatPearls chapters give different figures).
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Lumbar puncture (if CT negative and suspicion persists)
Elevated opening pressure; red cells that do not clear from tube 1 to tube 4; xanthochromia Only after brain imaging. Xanthochromia needs hours to develop — StatPearls chapters differ on the ideal timing.
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CT angiography · digital subtraction angiography
Location and size of the aneurysm DSA is the gold standard; patients with contrast allergy or kidney disease "need pre-procedure treatment to decrease the risk of an adverse reaction."
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Grading scales — GCS, Hunt and Hess (I–V), WFNS, Fisher
Higher grade = worse prognosis Hunt and Hess: grade 1 mild headache with slight nuchal rigidity … grade 5 "coma with decerebrate posturing." WFNS 3 or more (or enlarged ventricles) prompts a ventriculostomy per StatPearls.
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Transcranial Doppler
Rising velocities suggest vasospasm "A TCD is able to detect changes in velocity prior to the clinical sequelae of vasospasm"; angiography is required to diagnose and treat it.
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Serum sodium, urine sodium, volume status
CSW: hyponatremia, very high urine sodium, polyuria, hypovolemia; SIADH: euvolemic Correct sodium slowly (StatPearls gives limits of under 8 and no more than 10 mEq/L in 24 hours) to avoid osmotic demyelination; monitor sodium and neuro status frequently.
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Peripheral Diabetic Neuropathy DPN
Yearly comprehensive foot and neuropathy exam NIDDK · CDC
Reduced vibration (tuning fork), reduced pressure sensation (monofilament), abnormal gait or balance NIDDK: "If you have diabetes, you should get a thorough exam to test how you feel in your feet and legs at least once a year" — tuning fork at the great toes, a nylon monofilament, gait and balance. CDC: see the foot doctor every year, "more often if you have nerve damage."
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10-g (5.07) Semmes-Weinstein monofilament
Cannot feel the filament at tested sites = loss of protective sensation (ulcer risk) Tests 10 sites per foot (toes, metatarsal heads, arches, heel, first interspace). Loss of protective sensation "tends to occur later in the disease, sometimes even after a neuropathic ulcer develops" — a normal result does not rule out neuropathy.
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128-Hz tuning fork · ankle reflexes
Reduced or absent vibration; decreased ankle reflex Catch earlier large-fiber loss; timing how long the vibration is felt at the great toe helps "detect sensory deficits earlier and quantify severity."
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Foot inspection, pulses and temperature
Dry cracked skin, deformity, callus, ulcer; weak dorsalis pedis or posterior tibial pulses; hot spot Remove both shoes and socks for every exam. A temperature difference of more than 3–4 °C between feet may mean infection or acute Charcot foot.
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Blood tests to rule out other causes — vitamin B12, thyroid, kidney function
Normal, or a second treatable cause NIDDK: "Metformin use is among several causes of low vitamin B12 levels. If B12 deficiency is due to metformin, metformin can be continued with B12 supplementation."
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[Metformin] Vitamin B12 and blood counts FDA label (metformin)
Subnormal B12 in about 7% in 29-week trials "Measure hematological parameters annually and vitamin B 12 at 2 to 3 year intervals and manage any abnormalities."
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Orthostatic blood pressure (lying → standing)
Drop in BP on standing in autonomic neuropathy NIDDK: "blood pressure checks while you are lying down and then after you stand up."
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Nerve conduction studies / EMG
Only for atypical cases Indicated for "rapid symptom onset, severe neuromotor impairment, and asymmetrically abnormal sensation."
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Encephalitis Herpes simplex encephalitis (HSE)
CT or MRI before lumbar puncture
Exclude raised ICP / shift; MRI shows temporal-lobe changes in HSV Imaging helps "exclude increased intracranial pressure and the risk of uncal herniation prior to performing an LP." MRI "is more than 90% sensitive in detecting abnormalities with herpes simplex encephalitis"; CT "often shows no abnormalities in early infection."
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CSF HSV-1/HSV-2 PCR
Positive in HSV encephalitis "Amplified polymerase chain reaction (PCR) should be performed for HSV-1 and HSV-2 and has a sensitivity and specificity of 96% and 99%, respectively." An early negative PCR in a high-suspicion patient "should be repeated"; StatPearls, citing the 2008 IDSA guideline, advises continuing acyclovir meanwhile.
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CSF analysis
Lymphocytic pleocytosis, elevated protein, normal glucose; RBCs possible in HSV About "10% of patients will have normal CSF studies." In West Nile, neutrophils "may predominate early."
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EEG
Frequently abnormal in HSV encephalitis "EEG (electroencephalography) can identify abnormal brain waves by monitoring electrical activity in the brain."
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[West Nile] Virus-specific IgM / PCR (CSF and serum) CDC
Positive Consider WNV "in any person with an acute febrile or neurologic illness who has had recent exposure to mosquitoes, blood transfusion, or organ transplantation."
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[Anti-NMDAR] CSF anti-NMDAR IgG; pelvic ultrasound
Antibody positive; look for ovarian teratoma CSF antibody testing is "the gold-standard diagnostic evaluation"; "Transvaginal ultrasonography represents the most important screening test for young women." Exclude infection first.
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[Acyclovir] Serum creatinine, BUN, urine output FDA label (acyclovir injection)
Stable renal function StatPearls: "Dose adjustment of acyclovir for ideal body weight and baseline renal function is imperative"; label: in older adults "it may be useful to monitor renal function."
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Brain Tumors CNS tumors
MRI brain with contrast
Mass(es), edema; GBM: central necrosis with surrounding edema NINDS: MRI is "the gold standard for diagnosing CNS tumors"; for suspected metastases "fine-slice MR of the brain with contrast is the gold standard." GBM: "Central hypointensity in T1 due to necrosis and peripheral hyperintensities in T2/FLAIR sequences due to edema."
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Head CT (emergency department)
Hemorrhage, edema, asymmetry "A head CT is an excellent initial study to evaluate for acute intracranial findings."
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Biopsy (stereotactic or at resection)
Tumor type and grade "Biopsy confirmation … is critical." A stereotactic biopsy is used for deep, hard-to-reach tumors. Do not assume a lesion is a metastasis because of a past cancer.
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[GBM] MGMT promoter methylation
Methylated = better survival and benefit from alkylating chemotherapy Molecular marker guiding temozolomide benefit.
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Neurological and eye (papilledema) examination
Focal deficits; papilledema from raised pressure "A complete neurologic examination should be performed." "An ophthalmic examination should be performed to evaluate for papilledema."
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[TMZ] ANC and platelets before each cycle; liver tests TEMODAR label
Withhold until ANC ≥ 1.5 × 10⁹/L and platelets ≥ 100 × 10⁹/L Label: "Monitor absolute neutrophil count (ANC) and platelet count prior to each cycle and during treatment." Liver tests at baseline, midway through cycle 1, before each cycle and 2–4 weeks after the last dose. During concurrent chemoradiation, StatPearls recommends weekly CBC with differential and liver tests.
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[DEX] Glucose, HbA1c, electrolytes, blood pressure
Steroid hyperglycemia, electrolyte imbalance, BP rise StatPearls monitoring list for dexamethasone; "large doses can increase blood pressure."
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Huntington’s Disease Huntington disease (HD)
Genetic test — CAG repeat count in the HTT gene NINDS · MedlinePlus Genetics
36 or more repeats in people with HD (NINDS); 40 or more almost always causes the disorder (MedlinePlus Genetics) StatPearls: "The gold standard for evaluation is genetic testing, which is targeted testing of the CAG repeat size." NINDS: "The most accurate way to test for HD is to count the number of CAG repeats in a person’s HTT gene using DNA from a blood sample."
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Predictive (presymptomatic) testing — with genetic counseling NHS
A personal choice; usually offered at 18 or older (NHS) NHS: "It's your choice whether you have the test. As Huntington's disease cannot currently be prevented, some people choose not to get tested, especially if they do not have symptoms." "Your GP can arrange an appointment with a specialist called a genetic counsellor, who can help you decide." StatPearls: testing helps people "make informed decisions concerning the caregiver, finances, and reproduction," and "The optimal time to determine the genetic risk as well as discuss prenatal testing is before pregnancy."
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MRI or CT
Caudate atrophy ("boxcar appearance"); early HD may have normal scans StatPearls (Chorea): "The classical MRI finding in Huntington disease is caudate atrophy, which results in a boxcar appearance." NINDS: "people with early HD may have normal scans."
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Psychiatric evaluation, including suicidality
Cognitive, behavioral and functional deficits documented StatPearls (Chorea): evaluation includes "a psychiatric evaluation to assess deficits in cognitive, behavioral, and functional areas. Inquiry about suicidality is crucial."
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Swallowing and nutrition screening EHDN 2019
Serial weight and BMI; swallowing assessment EHDN (Grade C): "Regular assessment of swallowing disorders should be provided throughout the progression of the disease." "Screening tools for malnutrition [e.g., malnutrition Universal Screening Tool (MUST)] are recommended." EHDN recommends intervention "when unintended weight loss is higher than 10% within last 3–6 months."
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Hydrocephalus & Normal Pressure Hydrocephalus Hydrocephalus
[HYD] Emergency head CT
Enlarged ventricles StatPearls: "In cases of acute hydrocephalus, an emergency head computed tomographic (CT) scan is the first option to assess the ventricular size." NINDS: "Doctors may use CT in an emergency situation."
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MRI of the brain
Ventriculomegaly; in iNPH, enlarged Sylvian fissures with tight high-convexity sulci StatPearls: MRI "is the study of choice as it shows better the posterior fossa structures, can differentiate between brain tumors and degenerative diseases and can differentiate NPH from cerebral atrophy." In iNPH an Evans index of 0.30 or greater supports ventricular enlargement, "although values of 0.30 or less do not exclude iNPH."
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[NPH] Large-volume lumbar tap test StatPearls
Gait improves after CSF removal (positive test) StatPearls (iNPH): typically 30 to 50 mL removed, with assessment "at 2 to 4 hours and again the following day"; StatPearls (Hydrocephalus) cites 40–50 mL. "A negative tap test does not exclude iNPH." Opening pressure is often normal: "a single normal lumbar puncture does not exclude the diagnosis." If the tap test is equivocal, "External lumbar drainage may be considered."
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[NPH] Timed gait and turning measures, before and after the tap
Faster Timed Up and Go, fewer steps to turn StatPearls: "Objective gait metrics, including the Timed Up and Go test, gait speed, and number of steps required to turn, should be recorded alongside a brief cognitive assessment emphasizing executive function." "A reduction of approximately 5 seconds on the Timed Up and Go test supports responsiveness, although clinical judgment predominates."
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[HYD] Fundoscopic examination
Optic nerve swelling if pressure is raised NINDS: it "can show evidence of swelling that indicates elevated pressure in the skull, which may suggest hydrocephalus."
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[VALVE] Valve setting check FDA
Setting unchanged after MRI or magnet exposure FDA: "The only sure way to know if an adjustable shunt valve setting has changed is to have the pressure setting checked by a physician with an X-ray or specialized magnetic tool known as a shunt checker."
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Mental & Behavioral Health

Depression & Suicide Risk
Clinical evaluation (DSM-5 criteria) DSM-5-TR (APA)
≥ 5 symptoms in the same 2-week period, at least one being depressed mood or anhedonia, with functional impairment History, physical exam, and mental-health evaluation — and rule out any prior manic or hypomanic episode, which reclassifies the illness as bipolar disorder
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PHQ-9 StatPearls
Score ≥ 10 indicates possible major depressive disorder (scored 0–27) Used for screening, diagnosis, and monitoring treatment response — trend it across visits
Normal 9 items mirroring the DSM-5 MDD criteria
Suicide-risk screens (C-SSRS · ASQ · PSS-3)
C-SSRS rates the degree of ideation and intent; PSS-3 screens all clients presenting to acute care Tools are not substitutes for comprehensive clinical assessment — introduce screening by explaining its purpose and normalizing the questions
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Medical rule-outs (e.g., thyroid tests)
Checked to exclude conditions that mimic depression — classically thyroid disorders Thyroid abnormalities are also implicated in MDD itself; a new depression work-up is not complete on psychiatric history alone
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Severity rating scales (HAM-D · MADRS · Beck · Zung)
Elevated scores tracking episode severity HAM-D is clinician-administered (21 items, scored on the first 17); Beck and Zung are self-rated
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Cornell Scale for Depression in Dementia (CSDD) StatPearls
> 10 suggests major depression; > 18 definite major depression For older adults with cognitive impairment — 19 items combining patient and caregiver input
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Alcohol Use Disorder & Withdrawal AUD
CIWA-Ar score StatPearls / Open RN
Mild ≤ 8 · moderate 8–15 · severe > 15. Scores below 10 typically need no medication, and treatment thresholds vary by agency protocol A severity and dosing tool used once the diagnosis is established — not a diagnostic one. Most items depend on the patient answering questions, and it is not validated in critically ill, medically complex or postoperative patients; a head injury can also falsely raise the score.
Normal 0 (10 items, each 0–7 except orientation 0–4; max 67)
Diagnosis (clinical + DSM-5) DSM-5 / StatPearls
Withdrawal, withdrawal delirium, and AUD are diagnosed clinically by DSM-5 criteria. AUD = ≥ 2 of 11 criteria in 12 months: mild 2–3 · moderate 4–5 · severe ≥ 6 History and physical make this diagnosis — it is a clinical diagnosis, and no single lab confirms or excludes it.
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Blood alcohol concentration Michigan Medicine MAWS protocol
A positive BAC does not rule out withdrawal — significant withdrawal can occur while alcohol is still detectable Send a urine toxicology screen too — concomitant substance use can mimic or coexist with withdrawal.
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BMP/CMP + magnesium + phosphorus StatPearls / MAWS protocol
Check and replete electrolytes — magnesium and phosphorus especially Hypophosphatemia flags refeeding-syndrome risk, and magnesium deficiency undermines thiamine use. Hospital protocols add folic acid and a daily multivitamin, since these patients are often nutritionally deficient.
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Hepatic panel, CBC + markers of use StatPearls / MAWS protocol
AST, ALT, and GGT elevations mark chronic use; ethyl glucuronide detects use ~5 days back, carbohydrate-deficient transferrin ~2 weeks, phosphatidylethanol ~3 weeks Baseline work-up also includes a CBC with differential and a urine pregnancy test in women.
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AUD screening (AUDIT · AUDIT-C · SASQ · CAGE) USPSTF / MedlinePlus
AUDIT ≥ 8 may indicate AUD; CAGE ≥ 2 "yes" answers (Cut down · Annoyed · Guilty · Eye-opener) may signal AUD — cutoff of 1 for older adults USPSTF grade B: screen all adults with a validated brief instrument (SASQ or AUDIT-C). CAGE is still used but no longer preferred — better tests exist. Screening matters because many patients never volunteer their alcohol history.
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Schizophrenia & Psychotic Disorders
There is no diagnostic test StatPearls; MedlinePlus (NLM)
"No laboratory, psychometric, or radiologic studies currently exist for diagnosing schizophrenia." The diagnosis is made after "a detailed psychiatric history and mental status examination and after ruling out other psychiatric and medical causes of psychosis" Collateral information from family members or close contacts is essential — a patient with impaired insight cannot be the only historian. Every test below exists to exclude something else, not to confirm schizophrenia
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Initial evaluation laboratory panel StatPearls (Schizophrenia; Psychosis)
Work-up to exclude secondary causes of psychosis: urine toxicology screen, CBC and metabolic panel, urinalysis, TSH, liver function tests, vitamin B12 and HIV, with CT or MRI, EEG and lumbar puncture when indicated Organic causes to review include syphilis, HIV/AIDS, brain lesions, heavy-metal toxicity, delirium, metabolic and endocrine disorders and the dementias — which is why the work-up comes before the label
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Urine toxicology — and the gap in it
Screens for substances that cause psychotic symptoms. But "some substances which correlate to psychotic episodes — bath salts, certain synthetic strains of cannabis, psychedelics — may not show up on basic drug screen panels" The sequencing rule is absolute: "it is only when clinicians have officially ruled out a substance, medication-induced, or other underlying medical cause that one can consider a primary psychotic disorder." A negative screen does not close the question when the history suggests a novel agent
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ECG before specific agents StatPearls (Psychosis)
Consider when QTc risk is present — antipsychotics can prolong the QT interval Antipsychotics can cause "dangerous QT prolongation" — relevant in any patient with cardiac risk factors or other QTc-prolonging drugs
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Primary psychosis versus medical or neurologic psychosis — five discriminators
Age of onset — primary presents late teens to early thirties, medical/neurologic often after 40 · Pattern — primary is subtle with a prodrome, medical/neurologic is acute · Genetics — family history associates with primary · Context — primary appears during life stressors, medical/neurologic in healthcare settings · Modality — primary is "generally synonymous with auditory hallucinations," medical/neurologic correlates with all other types except auditory "The older the patient, the higher the risk for medical or neurological psychosis, especially in the hospital setting." In older adults the bedside rule is stronger still: visual hallucinations or illogical, disorganized thinking "can be considered signs of delirium unless proven otherwise, as primary psychotic disorders are rare to develop at an older age."
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Attention testing at the bedside
Ask the patient to recite the months of the year or the days of the week in reverse order — inattention is a common feature of delirium Delirious patients also have difficulty maintaining consciousness, which fluctuates throughout the day. In schizophrenia the deficit is in insight and judgment with a clear sensorium. The first priority in any altered mental status is "ruling out any life-threatening conditions, eg, hypoxia, ST elevation in case of a myocardial infarction, or hypoglycemia"
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Quantitative symptom rating scales
PANSS — 30 items across positive (7), negative (7) and general psychopathology (16) subscales, each rated 1 (absent) to 7 (extreme); a PANSS-6 short form correlates well with the full version. BPRS — 18 items for tracking change over time. WHODAS — health and disability across life domains These are severity and progress instruments for tracking symptoms and function, not diagnostic tests
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AIMS — the movement-disorder screen and its interval StatPearls (Extrapyramidal Side Effects)
Baseline screening before starting, then routine follow-up screening with a validated scale — the AIMS, the Extrapyramidal Symptoms Rating Scale or the Barnes Akathisia Rating Scale — plus prompt reassessment whenever a new or worsening movement appears This is a nursing responsibility, not a formality — tardive movements "may become permanent even after discontinuing the medication," so how early they are caught is the only variable the team controls
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Laboratory picture in neuroleptic malignant syndrome
Metabolic panel with electrolytes and creatinine, creatine kinase, urinalysis for myoglobinuria, and a blood gas for metabolic acidosis. Findings are "consistent with rhabdomyolysis with an elevated CK and acutely declining renal function," and leukocytosis is common, from 10,000 to 40,000/mm³ with a left shift No fetched source gives a numeric temperature or creatine kinase cut-off, and none should be taught. The CK "can be profound and typically correlates with disease severity." NMS is a clinical diagnosis — teach the pattern of fever with severe rigidity, altered mental status and autonomic instability, supported by rising CK, myoglobinuria and leukocytosis
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Bipolar Disorder
There is no test — the diagnosis is clinical
"Bipolar disorder is a clinical diagnosis that relies on careful longitudinal history and mental status examination, as no biomarker or neuroimaging modality has adequate sensitivity or specificity for routine diagnostic use." Accurate diagnosis requires identifying lifetime episodes of mania, hypomania, depression and mixed states, "ideally corroborated by collateral informants and prior treatment records." The collateral history is not a courtesy, it is a data source — poor insight in mania and hypomania makes the patient an unreliable historian about the very episodes the diagnosis depends on
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Initial medical work-up to exclude a secondary cause
Complete blood count · comprehensive metabolic panel · TSH and thyroid hormones · vitamin B12 and folate · urine toxicology · liver and renal function · pregnancy testing when indicated. Brain imaging by CT or MRI where an organic cause is suspected, "especially in elderly or very young patients"; routine neuroimaging is not recommended for diagnosis Hyperthyroidism is the classic mimic — "Physiologic conditions that may mimic mania include hyperthyroidism, hypertensive urgency, hypercortisolemia, hyperaldosteronism," and "A complete blood count (CBC), complete metabolic panel (CMP), thyroid panel, and a urine drug screen are some of the basic laboratory values needed in assessing a manic patient." Other mimics: stimulant, cocaine, amphetamine, PCP and nicotine intoxication; hallucinogens; excessive steroid or growth hormone use; hypertensive urgency; hypercortisolemia
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Red flags for a secondary cause of mania
First onset after age 50 · abrupt onset · no personal or family psychiatric history · neurologic abnormalities · cognitive impairment · fluctuating consciousness · a new medical illness · onset after a medication exposure · poor response to evidence-based treatment Any one of these should redirect the workup toward a medical cause before a psychiatric label is applied. In an older adult presenting with new mania, investigate stroke, thyroid dysfunction and dementia
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Unipolar versus bipolar depression — the history questions
Features that raise suspicion of bipolar disorder: depression beginning early, especially before age 25; recurrent, high-frequency depressive episodes; psychotic features; postpartum mood episodes; a strong family history of bipolar disorder; and antidepressant-associated mood switching or activation The problem is structural: "cross-sectionally, bipolar depression is typically indistinguishable from unipolar depression," and past hypomanic or manic episodes "are often not spontaneously reported by patients" — so they must be asked about directly. The average delay to a correct diagnosis is 5 to 10 years. On conversion, quote the figure with its window and owner: StatPearls reports 20% to 30% transitioning within 3 years of a major depressive disorder diagnosis, and separately that subthreshold hypomanic symptoms occur in up to 40% of patients with major depressive disorder — symptoms, not a diagnosis
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Screening instruments — useful, and not diagnostic
Mood Disorders Questionnaire — sensitivity 80%, specificity 70%. Hypomania Checklist 32 — sensitivity 82%, specificity 57%. Also named: the Young Mania Rating Scale (11 items on the past 24 hours, with a parent version) and the Altman Self-Rating Mania Scale These tools "demonstrate moderate sensitivity," but "their specificity is limited," so they are to be used "as adjuncts rather than diagnostic instruments, with positive results prompting structured clinical interviews." A negative screen does not exclude bipolar disorder; the Hypomania Checklist’s 57% specificity means a positive one is often wrong too
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Lithium serum level — the target range and how to draw it FDA-approved prescribing information for lithium carbonate (current label)
0.8 to 1.2 mEq/L for acute goals; 0.8 to 1.0 mEq/L for maintenance goals. Draw the sample "immediately prior to the next dose when lithium concentrations are relatively stable (i.e., 12 hours after the previous dose)." Beyond routine maintenance monitoring, re-check "after any change in dosage, concurrent medication (e.g., DIURETICS, NON-STEROIDAL ANTI-INFLAMMATORY DRUGS, RENIN-ANGIOTENSIN SYSTEM ANTAGONISTS, or METRONIDAZOLE), marked increase or decrease in routinely performed strenuous physical activity (such as an exercise program) and in the event of a concomitant disease" UNITS FIRST, because this page moves between two of them and the comparison is the whole point. Lithium is monovalent, so 1 mEq/L and 1 mmol/L are the same number — the FDA label writes the toxic threshold as "≥1.5 mEq/L" while the toxicity literature writes the identical threshold as 1.5 mmol/L. Read every figure below in whichever unit it is printed and compare them directly. The range is FDA product labeling, cited directly: "Acute Manic or Mixed Episodes (patients 7 years and older): Titrate to serum lithium concentrations 0.8 to 1.2 mEq/L"; "Maintenance Treatment for Bipolar I Disorder (patients 7 years and older): Titrate to serum lithium concentrations 0.8 to 1 mEq/L." The label states the squeeze outright: "The toxic concentrations for lithium (≥1.5 mEq/L) are close to the therapeutic range (0.8 to 1.2mEq/L)." And the label is explicit that the number is not the whole answer: "TOTAL RELIANCE MUST NOT BE PLACED ON SERUM CONCENTRATIONS ALONE. Accurate patient evaluation requires BOTH clinical and laboratory analysis." The boxed warning frames the whole problem: "lithium toxicity is closely related to serum lithium levels and can occur at doses close to therapeutic levels. Before initiating therapy, ensure that lithium levels will be able to be measured promptly and accurately"
Normal Lithium is not normally present; the therapeutic window is narrow and toxicity begins close to it
Baseline and ongoing tests before and during lithium
Before the first dose: kidney and thyroid function tests and a recorded weight. There is a cardiac reason to think about an ECG as well — lithium "can cause abnormal electrocardiographic (ECG) findings and risk of sudden death" — but no source behind this page sets a baseline-ECG age rule, so none is printed. During therapy: those tests once or twice annually, plus urinalysis, BUN and creatinine, thyroid studies and calcium Each has a reason. Renal function because lithium is cleared entirely by the kidney; thyroid because lithium accumulates in the thyroid gland, inhibiting synthesis and release, potentially causing hypothyroidism; calcium because prolonged use is associated with persistent hyperparathyroidism and hypercalcemia; weight because lithium causes weight gain. Nutrition and hydration labs — sodium, hematocrit, albumin, prealbumin — are added in mania because intake collapses
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Interpreting a lithium level in suspected toxicity EXTRIP-aligned bands, as reported by StatPearls
Clinical findings of toxicity "commonly occur at lithium concentrations greater than 1.5 mmol/L," traditionally categorised as mild 1.5–2.5, moderate 2.5–3.5, and severe above 3.5 mmol/L. A second source names above 2.5 mEq/L as a medical emergency even in an asymptomatic client The number is the weakest piece of evidence you have. Levels "may not correlate with severity, particularly in cases of chronic toxicity"; acute toxicity is often asymptomatic at high concentrations while chronic toxicity causes neurologic impairment at relatively lower concentrations; symptoms may worsen as the level falls, because distribution into the central nervous system is slow; and samples collected in lithium heparin tubes read falsely high. Interpret levels "in conjunction with clinical findings"
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Anxiety Disorders & PTSD PTSD
Rule out the body first
Thyroid function tests · blood glucose · toxicology screen · echocardiography where indicated. The nursing text names the conditions being excluded: hyperthyroidism, hypoglycemia, hypercalcemia, hyperkalemia, hyponatremia or hypoxia There is no test that makes any of these diagnoses — the investigations exist to exclude the mimics, not to confirm the disorder. For panic disorder the sourced statement is categorical: "there are no specific laboratory, radiographic, or other tests required to diagnose panic disorder." The same logic governs the trauma disorders, where VA/DoD 2023 places diagnosis with a validated structured clinician-administered interview (Rec 2) rather than with any laboratory value
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The generalized anxiety differential
Hyperthyroidism · pheochromocytoma · chronic obstructive pulmonary disease · transient ischemic attack · epilepsy · bipolar disorder · use of caffeine, decongestants and albuterol Thyrotoxicosis appears on this differential and on the bipolar one, which is why a thyroid-stimulating hormone level belongs in almost every new psychiatric workup. Note that two items — decongestants and albuterol — are things the patient may be buying or inhaling for something else entirely
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The panic differential — an emergency-department problem
Angina · asthma · congestive heart failure · mitral valve prolapse · pulmonary embolism · substance use disorder · other mental health disorders associated with panic attacks The reason this list matters is mortality, not thoroughness. Panic disorder carries "a high risk of coronary artery disease" with "the risk of sudden death increased compared to the general population," and named comorbidities include asthma, COPD, irritable bowel syndrome, hypertension and mitral valve prolapse. A prior diagnosis of panic disorder is not protective
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Screening instruments — by name, and without a score
GAD-7 for generalized anxiety, "validated as a diagnostic and severity assessment tool" and usable to monitor. For PTSD: the PTSD Checklist for DSM-5 (PCL-5), the Trauma Symptom Checklist-40, the Primary Care PTSD Screen for DSM-5 (PC-PTSD-5), and the Clinician-Administered PTSD Scale as a 30-item structured interview. For PTSD screening specifically, VA/DoD 2023 suggests the PC-PTSD-5 (Rec 1, Weak for) — a five-item questionnaire whose validation found "a score of three as maximally sensitive and four as maximally efficient" — and immediately adds the sentence that governs every number on this page: "no screening measure or cutoff point should be the sole basis for diagnosis." For confirming the diagnosis it suggests a validated structured clinician-administered interview (Rec 2), and for tracking change over time a validated instrument such as the PCL-5 (Rec 3) One cut-off on this page is sourced and no other is. VA/DoD 2023 suggests the PC-PTSD-5 for screening (Rec 1, Weak for), recording that validation found "a score of three as maximally sensitive and four as maximally efficient" — and, in the same passage, that "no screening measure or cutoff point should be the sole basis for diagnosis." Quote the number only with that sentence attached, and do not attach a cut-off to GAD-7 or PCL-5, because none is sourced here. Confirmation belongs to a validated structured clinician-administered interview (Rec 2, Weak for), and tracking change over time to a validated instrument such as the PCL-5 (Rec 3, Weak for). The psychiatric evaluation "is the most important component of diagnosing PTSD"
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How to ask about trauma
Four general screening questions: "Do you think about the traumatic event more than you would like to?" · "Do you have nightmares or flashbacks related to the trauma?" · "Do you avoid people or triggers associated with the trauma?" · "Are you struggling with feelings of persistent sadness?" The rule that changes practice: "the specific details of the trauma are usually NOT necessary for obtaining a PTSD diagnosis." Details are needed only for certain psychotherapies, "which the patient should consent to before initiating." Respect patient boundaries and ask how deeply or superficially the patient prefers to discuss the topic, and in sexual-assault trauma consider the gender of provider and patient, since many survivors "may have difficulty being in an interview room alone with the gender of their perpetrator"
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The PTSD mental status examination
Appearance — "scars, wounds, and other deformities may be present due to prior traumatic experiences." Behavior — hypervigilance; observe eye contact. Affect — fearful, anxious, apathetic or depressed, and often "constricted affect consistent with feeling numb." Thought content — assess suicidal ideation and self-harm On insight: patients "commonly have a fair understanding of their illness, although specific populations may minimize their symptoms." Assess whether the PTSD is current — "over time, patients may no longer meet the diagnostic criteria," and some "may over-attribute PTSD as a primary disorder despite no longer meeting the diagnostic criteria"
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Safety assessment after trauma
Assess suicidal ideation, intent, plan, prior self-harm, agitation, severe insomnia, substance use, and available supports Available supports is a clinical variable here, not a social nicety: people with a well-established support system "are less likely to develop PTSD," and those who feel isolated are "more likely to develop an acute stress disorder and/or PTSD." Note also that "patients may initially find it difficult to describe their experiences, and more than 1 assessment may be needed." The Patient Safety Screener is named as a brief suicide-risk screen for acute care settings
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Distinguishing PTSD from its look-alikes
Acute stress disorder — heavy symptom overlap, so "the onset and duration of the symptoms help in making the final diagnosis." Dissociative disorders — present without the other PTSD symptomatology. Adjustment disorder — symptoms in response to an identifiable stressor that need not be trauma, occurring within 3 months and not persisting more than a further 6 months. Brief psychotic disorder — under 1 month but defined by delusions, hallucinations or disorganized speech, which are "not typical of ASD" Traumatic brain injury is on the acute-stress differential and is easy to miss after the same collision that caused the psychological trauma. Complex PTSD is described as an ICD construct adding persistent disturbances in self-organisation to core PTSD symptoms; major depressive disorder is usually comorbid rather than exclusive
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Substance Use & Overdose SUD
Initial evaluation for opioid use disorder
A full social and mental health history, including "history of injuries, trauma, previous surgeries, and hospitalization… to identify gateways for opioid use." Urine drug screening for opioids should be performed BEFORE starting treatment and regularly at subsequent visits "If the patient uses intravenous drugs, tests should be ordered to screen for HIV and hepatitis B and C." That is not defensive medicine — hepatitis A, B or C is positive in approximately 80% to 90% of injection opioid users, and HIV positivity has been reported as high as 60% in some regions and as low as 10% in others
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Urine toxicology — and the three gaps in it
Positive for "most opioids such as morphine, heroin, codeine, oxycodone, and propoxyphene for 12 to 36 hours after use" Gap one: "methadone, buprenorphine, and LAAM will NOT be detected in positive urine opiate tests, and they must be specifically tested." Gap two, on the stimulant side: "ingestion of some amphetamines… will not reliably result in a positive test," while false positives arise from "pseudoephedrine, mebeverine, metoprolol, tetracaine, dimethylamylamine, aripiprazole, and ranitidine" — so "clinicians should not rely on drug metabolite testing alone." Gap three: there is no diagnostic test for opioid withdrawal at all; toxicology is run "to rule out withdrawal from any other drugs"
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Baseline laboratory work
ECG, complete blood count, blood alcohol level and basic metabolic panel For suspected stimulant toxicity the panel widens with a purpose attached to each test: a basic metabolic panel for dehydration and hyponatremia; ECG, chest x-ray and troponin for coronary ischemia, myocardial infarction and aortic dissection; head CT for haemorrhagic stroke causing neurologic deficits; and serum creatine kinase and lactic acid to identify "muscle damage and tissue ischemia related to tonic-clonic seizures, myoclonus, or hyperthermia"
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COWS — the Clinical Opiate Withdrawal Scale COWS via StatPearls, citing the instrument’s original publication
11 signs and symptoms of opioid withdrawal, total score 0 to 47, banded as mild 5–12 · moderate 13–24 · moderately severe 25–36 · severe above 37 The score is not paperwork — it is the gate on the first buprenorphine dose, which is withheld until the score exceeds 10. COWS exists precisely because buprenorphine "can precipitate withdrawal in opioid-dependent patients who are NOT experiencing any withdrawal symptoms," and it is administered serially "to track changes in the severity of withdrawal symptoms over time or in response to treatment." The per-item scoring is not stated here because the two fetched sources give arithmetically incompatible descriptions of it
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CIWA-Ar — named here only for the pairing
The alcohol instrument, described as "the most widely used scale to determine the need for medically supervised withdrawal management" Learn the pairing: CIWA-Ar for alcohol, COWS for opioids. The Alcohol Withdrawal page owns CIWA-Ar in full, including its severity bands and the caution that it is a severity tool rather than a diagnostic one — this page deliberately does not restate different numbers
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Prescription drug monitoring programs CDC Clinical Practice Guideline for Prescribing Opioids for Pain, United States, 2022
An electronic system tracking controlled-substance prescriptions. "PDMPs play a crucial role in identifying patients who may be at risk of overdose," and providers "should routinely review PDMP data," including "when initiating the use of opioids to alleviate acute, subacute, or chronic pain" The threshold that pairs with it, in the guideline’s own words: "If a patient’s opioid dosage for all sources of opioids combined reaches or exceeds 50 MME/day, clinicians should implement additional precautions, including increased frequency of follow-up, and offer naloxone and overdose prevention education to both the patient and the patient’s household members." CDC 2022 also records why the number sits there — increases above 50 MME/day "are unlikely to provide substantially improved pain control for most patients while overdose risk increases." And the co-prescribing caution belongs beside it: "use particular caution when prescribing benzodiazepines or other sedating medications with opioid pain medication… and check the prescription drug monitoring program (PDMP) database"
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Discharge criteria after a naloxone reversal
For respiratory depression fully reversed with 0.4 to 2 mg of naloxone, observe for 2 to 4 hours, and require all of: Glasgow coma scale 15 · no further naloxone needed · oxygen saturation at least 92% on room air · respiratory rate at least 10 · pulse between 50 and 120 · blood pressure between 110/90 and 140/90 mm Hg · tolerating clear liquids and ambulating with no withdrawal symptoms · someone to drive them home and monitor them for the next 12 to 24 hours Waking up is not on that list. Naloxone’s half-life is 30 to 80 minutes and is shorter than methadone, fentanyl and buprenorphine, so re-sedation is expected rather than surprising. Monitoring windows differ by source and both should be named: at least 4 hours from the last naloxone dose per the nursing text, and 6 to 12 hours per StatPearls, with longer monitoring for long-acting opioids
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Eating Disorders AN · BN · BED
History, physical examination and a clinical diagnosis
"The diagnosis will come from the history and physical examination." Obtain "the height, weight, vital signs, and orthostatic blood pressures," and the client’s own view of the problem — "Care planning that does not address their perspective will not be effective." Rule out medical causes of weight loss: "celiac disease, hyperthyroidism, inflammatory bowel disease, malignancy, poorly controlled diabetes mellitus, primary adrenal insufficiency, and tuberculosis." A positive stool or urine laxative screen is not needed for a bulimia diagnosis
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Electrolytes, blood count and metabolic panel
Anorexia: coagulation panel, complete blood count, complete metabolic profile, 25-hydroxyvitamin D, TSH, and urine testing including beta-hCG and drugs. Bulimia: metabolic panel with electrolytes, liver and kidney function and calcium, and a blood count — "If severe, also obtain serum magnesium and phosphorous as well as the electrocardiogram." Expect hypokalemia and anemia from starvation, and hypokalemia, hyponatremia and hypochloremic metabolic alkalosis from purging No reference ranges are printed here on purpose — the sources behind this page give none. During refeeding, compare each potassium, phosphate and magnesium result with the patient’s own pre-feeding baseline (see the ASPEN criteria below). "Assess lab values (K+, Na+, Mg++, phosphate) frequently."
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Electrocardiogram
"An electrocardiogram is recommended to assess for life-threatening arrhythmias." Look for bradycardia, arrhythmia and a prolonged QTc in a patient with low potassium or magnesium Hypokalemia "can contribute to QTc prolongation," and low potassium with low magnesium can produce torsades de pointes
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Refeeding syndrome — ASPEN 2020 severity criteria ASPEN Consensus Recommendations for Refeeding Syndrome (2020)
A fall in any one, two or three of phosphorus, potassium and/or magnesium of 10–20% (mild), 20–30% (moderate), or more than 30% and/or organ dysfunction, or thiamine deficiency (severe) — "occurring within 5 days of reintroduction of calories" Hypophosphatemia is the hallmark. ASPEN, as summarized by StatPearls, checks magnesium, phosphorus and potassium before feeding starts and "every 12 hours for the first 3 days" in high-risk patients. Albumin and prealbumin do not help — "These markers are unreliable as they are acute-phase reactants"
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Body mass index (adults) — a screen, not a diagnosis
Below 18.5 underweight · 18.5–24.9 healthy weight · 25.0–29.9 overweight · 30.0 or higher obese; children and teens use percentiles, with below the 5th percentile underweight "BMI is a screening method and does not take into account muscle mass, bone density, overall body composition, racial, and sex differences." A patient can meet every anorexia criterion above a BMI of 18.5 (‘atypical anorexia nervosa’), and bulimia occurs at any weight
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Bone density and further imaging
DEXA to measure bone density; StatPearls adds an echocardiogram when BMI is very low and DEXA when amenorrhea has lasted more than 9 months Decreased bone density and "early onset osteoporosis" are long-term consequences of starvation
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Admission criteria — two sources, two cut-offs, both attributed
Open RN: "Common criteria for hospitalization include extreme electrolyte imbalance, weight below 75% of healthy body weight, arrhythmias, hypotension, temperature less than 98 degrees Fahrenheit, or risk for suicide." StatPearls (anorexia): medical instability — bradycardia, dehydration, hypoglycemia, hypokalemia or other electrolyte imbalances "indicative of refeeding syndrome," hypothermia, hypotension, organ compromise — high suicide risk, persistent severe purging "multiple times a day," or "Severe anorexia nervosa (less than 70% of ideal body weight or acute weight loss with food refusal)" These are two different numbers from two different sources, measured against two different reference weights — do not merge them into one. What both share is the qualitative picture: electrolyte derangement, arrhythmia, hypotension, hypothermia and suicide risk. Compulsive exercise alone is "not a sole indication for hospitalization"
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Behavioral Emergencies & Violence Risk Acute agitation
First tests in any agitated patient
"Initially, a point-of-care glucose test, oxygen saturation measurement, and urine toxicology screen are useful." Suspected intoxication or withdrawal adds a blood alcohol level and liver function tests; suspected delirium adds a complete blood count, comprehensive metabolic panel, urinalysis and a head CT The point is to find a reversible medical cause — hypoglycemia, hypoxia, infection, drugs. "After the client is restrained, the cause of their agitation will be evaluated to determine if it is medical, psychiatric, or substance-use related"
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Electrocardiogram
QTc prolongation from overdose, cardiac disease or the tranquilizing drugs themselves Haloperidol with lorazepam carries a risk of a "prolonged QT interval," and, as StatPearls reports from ACEP, droperidol carries "a black box warning for QT prolongation"
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Creatine kinase
Raised in rhabdomyolysis after prolonged struggling against restraints "Traumatic rhabdomyolysis has been associated with prolonged physical restraints, especially in individuals actively fighting against the restraints"
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Behavioural Activity Rating Scale (BARS)
An objective agitation score; 4 is the reference point Project BETA: "Any score other than a 4 should trigger an evaluation by a clinician." A score of 1 — difficult to arouse or unarousable — warrants transfer to a medical emergency department
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The 1-hour face-to-face evaluation (restraint or seclusion for violent or self-destructive behaviour) CMS — 42 CFR 482.13(e)(12)
Within 1 hour of initiation, a physician, other licensed practitioner or trained RN evaluates "The patient’s immediate situation," "The patient’s reaction to the intervention," "The patient’s medical and behavioral condition," and "The need to continue or terminate the restraint or seclusion" If a trained RN performs it, the RN must consult the attending physician or other licensed practitioner as soon as possible afterwards
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Obsessive-Compulsive Disorder OCD
Clinical assessment StatPearls, NIMH
Obsessions and/or compulsions that are time-consuming (more than an hour a day) or cause marked distress or impairment, not better explained by a substance, medical condition or other mental disorder NIMH: a provider will "ensure other illnesses or conditions are not causing your symptoms" and may refer to a mental health professional. "OCD frequently remains both underdiagnosed and undertreated" (StatPearls).
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Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) StatPearls
Scored 0 to 40; higher = more severe "the most widely accepted tool to screen for OCD is the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS)." "The Y-BOCS rates on a scale from 0 to 40, with 40 indicating the most severe symptomatology" (StatPearls).
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Safety and comorbidity screen StatPearls, FDA labels
Suicide risk, risk to others, depression, bipolar disorder, other anxiety disorders "Safety assessments are also conducted to look for immediate risks to the patient or others." "A striking 90% of individuals with OCD meet the criteria for at least one additional psychiatric disorder" (StatPearls). Labels: "A major depressive episode may be the initial presentation of bipolar disorder."
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Mental status picture StatPearls
Well groomed, visibly anxious; insight usually intact; no hallucinations "Patients generally present as well-groomed but exhibit visible anxiety." "Unlike some other psychiatric disorders, hallucinations or illusions are seldom observed in OCD patients" (StatPearls).
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Clomipramine monitoring StatPearls
ECG at baseline and after the desired effect; weight, BMI, fasting glucose and lipids "Due to the risk of QTc prolongation and arrhythmia, electrocardiogram testing is recommended at baseline and after achieving the desired clinical effect." Metabolic monitoring is "recommended before and during treatment" (StatPearls).
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Personality Disorders Borderline personality disorder (BPD)
Longitudinal clinical assessment StatPearls, NIMH
Pattern seen over time, ideally outside an acute psychiatric episode "Diagnosis of a personality disorder is based on the longitudinal observation of an individual's behaviors to assess their functioning over time." "If possible, personality disorders should be diagnosed when there is not a concurrent acute psychiatric condition" (StatPearls). BPD "is usually diagnosed in late adolescence or early adulthood" (NIMH).
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Medical and substance evaluation StatPearls, NIMH
Rule out medical causes, especially if symptoms first appear in midlife "If the symptoms are first presenting in midlife, the individual should be evaluated for another medical condition or an unrecognized substance use disorder" (StatPearls). NIMH: "A medical exam can further rule out other possible causes."
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Mental status and safety screen StatPearls, Open RN
Ask about self-harm, suicide and harming others at every assessment StatPearls: assess "thoughts of self-harm, suicidality, or harming others," and "individuals with personality disorders should be screened for suicidal ideation regularly." Open RN: introduce suicide screening "in a way that helps the client understand its purpose."
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Co-occurring conditions NIMH, StatPearls
Depression, PTSD, bipolar disorder, anxiety, substance use and eating disorders are common with BPD NIMH lists these; "symptoms of borderline personality disorder occur in the absence of significantly elevated mood seen during manic or hypomanic episodes, which is a key feature of bipolar disorder." "The prevalence of ASPD in patients with alcohol use disorder ranges from 16% to 49%" (StatPearls).
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Attention-Deficit/Hyperactivity Disorder (Adult) ADHD
Clinical interview and rating scales NIMH, StatPearls
Persistent, impairing symptoms across settings; symptoms began before age 12 NIMH: "adults must have shown symptoms much earlier, starting before age 12." "Adults or adolescents over 16 years must show five (instead of six) symptoms of inattention or hyperactivity and impulsivity," lasting "at least 6 months." "Complete clinical interviews, behavior rating scales, or symptom checklists to determine whether you meet the criteria for a diagnosis of ADHD." StatPearls names the Brown Attention Deficit Disorder Scale for adults.
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Collateral history NIMH
Reports from partner, family, school records "Diagnosing ADHD in adulthood is complicated by the need to show symptoms before age 12. For this reason, a diagnosis relies heavily on past reports of behavior." Clinicians "may ask to talk to people who know you well, such as a partner, family members, and friends" (NIMH).
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Rule out mimics and co-occurring conditions StatPearls
Mood, anxiety, sleep, substance use and thyroid problems considered "It should not be diagnosed in the context of symptoms from another disorder, for example, a psychotic episode or manic episode." "Substance abuse disorders should also be carefully examined." A physical exam "can still be used to exclude medical causes such as thyroid problems" (StatPearls).
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Pre-stimulant screening FDA label
Cardiac history, BP, HR; abuse/misuse risk; mania risk CONCERTA label: "Prior to treating patients with CONCERTA, assess: For the presence of cardiac disease"; "Before prescribing CONCERTA, assess each patient's risk for abuse, misuse, and addiction"; "screen patients for risk factors for developing a manic episode (e.g., history of depressive symptoms or a family history of suicide, bipolar disorder, or depression)."
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Endocrine

Diabetes Mellitus (Type 1 & 2) DM
Hemoglobin A1C ADA 2026; NIDDK (The A1C Test & Diabetes)
≥ 6.5% is diagnostic (NGSP-certified lab method); 5.7–6.4% is prediabetes. Treatment goal for many nonpregnant adults: < 7%, individualized The 3-month average — no fasting required. Goals loosen with frailty, limited life expectancy, or severe comorbidity, and tighten when healthy with low treatment risk
Normal < 5.7%
Fasting plasma glucose (FPG) ADA 2026
≥ 126 mg/dL is diagnostic (fasting = no caloric intake ≥ 8 h); 100–125 mg/dL is impaired fasting glucose (prediabetes) Screen all adults no later than age 35 — earlier at any age with BMI ≥ 25 kg/m² (≥ 23 in individuals of Asian ancestry) plus risk factors; rescreen at least every 3 years
Normal < 100 mg/dL
2-hour OGTT (75-g load) ADA 2026
≥ 200 mg/dL at 2 hours is diagnostic; 140–199 mg/dL is impaired glucose tolerance (prediabetes)
Normal < 140 mg/dL at 2 h
Random plasma glucose ADA 2026
≥ 200 mg/dL with classic hyperglycemia symptoms or hyperglycemic crisis is diagnostic on its own Without unequivocal hyperglycemia, diagnosis requires two abnormal results — different tests drawn at the same time, or the same test repeated
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Capillary glucose / CGM (treatment targets) ADA 2026
Preprandial 80–130 mg/dL · peak postprandial < 180 mg/dL · CGM time-in-range > 70%, time < 70 under 4%, time < 54 under 1% The numbers the bedside nurse acts on every shift — and < 70 mg/dL is the hypoglycemia action line (level 1 ≥ 54, level 2 < 54, level 3 = needs assistance)
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Islet autoantibodies & C-peptide ADA 2026
GAD65, IA-2, ZnT8, or insulin autoantibodies positive in type 1; C-peptide low when β-cell function is lost Ordered when the phenotype overlaps type 1 — younger age, unintentional weight loss, ketoacidosis, short time to insulin — because the answer changes lifelong therapy
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Diabetic Ketoacidosis DKA
Blood glucose ADA/EASD 2024
≥ 200 mg/dL (11.1 mmol/L) — or any glucose with a known history of diabetes Older criteria taught > 250 mg/dL, and it still appears on exams. Glucose can be < 250 in euglycemic DKA (think SGLT2 inhibitors) — never rule DKA out on glucose alone
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β-hydroxybutyrate (blood ketones) ADA/EASD 2024
≥ 3.0 mmol/L (or urine ketones ≥ 2+) Blood β-hydroxybutyrate is preferred over urine nitroprusside testing; resolution target is < 0.6 mmol/L — the number that finally lets the insulin drip stop
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pH (ABG/VBG) ADA/EASD 2024
< 7.30 · severity: mild > 7.25 · moderate 7.0–7.25 · severe < 7.0 Severity travels with mentation: alert in mild, drowsy in moderate, stupor/coma in severe. pH < 7.0 is also the only threshold at which bicarbonate is considered
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Serum bicarbonate ADA/EASD 2024
< 18 mmol/L · severity: 15–18 mild · 10 to < 15 moderate · < 10 severe The classic cutoff of < 15 mEq/L still circulates in older materials; the 2024 consensus criterion is < 18
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Anion gap StatPearls
Elevated — > 14–15 mEq/L The gap is the ketoacid load. Watching it close is watching the DKA resolve — the classic resolution set used gap ≤ 12 as a criterion
Normal ≈ 12 mEq/L (reference)
Serum potassium ADA/EASD 2024
Usually normal or elevated at presentation — despite a total-body deficit of 3–6 mmol/kg The most important lab of the sequence: check it before insulin, and if < 3.5 mmol/L, hold insulin and replace potassium first
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Hyperosmolar Hyperglycemic State HHS
Plasma glucose ADA/EASD 2024
≥ 600 mg/dL — the diagnostic threshold; values often run far higher Contrast DKA, which is diagnosed from ≥ 200 mg/dL — in HHS the glucose itself is the extreme finding
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Serum osmolality ADA/EASD 2024
Effective osmolality > 300 mOsm/kg or total > 320 mOsm/kg — the defining feature Effective = 2[Na⁺] + glucose (mmol/L); total adds urea. Mentation should track it, and poor mentation < 320 means look for another cause
Normal ≈ 280–290 mOsm/kg (HHS resolves below 300)
Ketones (beta-hydroxybutyrate) ADA/EASD 2024
BHB < 3.0 mmol/L (or a urine ketone strip less than 2+) — significant ketonemia absent Quantitative serum or point-of-care BHB is preferred over urine strips for diagnosis and monitoring; BHB ≥ 3.0 with hyperosmolality = mixed DKA-HHS, treated as DKA
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pH & bicarbonate ADA/EASD 2024
pH ≥ 7.3 and bicarbonate ≥ 15 mmol/L — no significant acidosis Typical values run near normal with a normal anion gap; the ≥ 7.3 / ≥ 15 floor allows the mild acidosis of severe dehydration and pre-renal failure
Normal Bicarbonate ~22–32 mmol/L
BMP — sodium, potassium, BUN/creatinine ADA/EASD 2024
K⁺ is the gatekeeper lab: insulin is postponed until K⁺ > 3.5 mmol/L. BUN/creatinine often elevated — acute kidney injury is a common complication An initial rise in sodium during fluid therapy is expected — as glucose falls, water re-enters cells and measured Na⁺ climbs — and is not by itself an indication for hypotonic fluids (ADA/EASD 2024 consensus)
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Precipitant hunt — cultures, chest x-ray, ECG, CT head as indicated
Positive findings point to the trigger: infection (30–60% of cases), MI, stroke An ECG matters even without chest pain — MI can precipitate HHS silently; CT head if the neuro picture doesn’t fit the osmolality
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Hypothyroidism & Myxedema Coma
TSH Endotext
Elevated in primary hypothyroidism — the first-line test, because the pituitary amplifies: a 2-fold T4 change can move TSH up to 100-fold In central disease TSH is low or inappropriately normal — central hypothyroidism can never be diagnosed on TSH alone; pair it with free T4
Normal ≈ 0.4–4.0 mU/L (some sources extend the upper limit to 4.5) — assay- and laboratory-specific
Free T4
Low (below the reporting lab’s own reference interval) in overt disease; normal with an elevated TSH = subclinical hypothyroidism Free — not total — T4 is measured, because protein-bound hormone can’t enter tissues. No universal numeric range exists: free-hormone assays require method-specific reference intervals, so read the flag against the lab’s own range
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Thyroid peroxidase (TPO) antibodies
Positive in > 90% of Hashimoto thyroiditis — confirms the autoimmune cause Positive TPO antibodies roughly double the risk that subclinical disease progresses to overt hypothyroidism
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Subclinical pattern — when to treat ATA/AACE (per StatPearls)
TSH elevated, free T4 normal; ATA and AACE recommend levothyroxine when TSH > 10 mIU/L, or with symptoms, positive TPO antibodies, or in women of reproductive age Progresses to overt disease at ~2–6% per year (3–8% with TSH > 10 plus TPO positivity)
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Myxedema-coma workup: Na⁺, glucose, CPK, cultures
Hyponatremia with low serum osmolality · hypoglycemia · elevated creatine phosphokinase · normocytic or macrocytic anemia A septic workup (cultures, chest x-ray) is standard — infection is the most common precipitant and may hide behind the hypothermia
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ECG & ABG in crisis
ECG: low voltage, variable block, prolonged QT. ABG: hypoxia, hypercapnia, acidosis The rising CO₂ is the coma mechanism in progress — trend it and anticipate mechanical ventilation
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TSH on therapy (monitoring)
Recheck 4–8 weeks after starting or changing a dose, then every 6–12 months once stable The recheck can’t come sooner: T4’s half-life is 7–10 days, so steady state takes weeks — an early draw misleads
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Hyperthyroidism & Thyroid Storm Thyrotoxicosis
TSH StatPearls
Low/suppressed — < 0.01 mU/L in overt disease; the pituitary shuts its signal off in the face of hormone excess TSH stays suppressed for ~6 months after treatment starts, so it cannot steer early therapy — follow free T4/total T3 every 4–6 weeks instead
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Free T4 & total T3 ATA 2016 (per StatPearls)
Elevated (one or both) confirms overt disease; suppressed TSH with normal T3/T4 = subclinical; elevated T3 alone = "T3 toxicosis" (T3 often rises first) Subclinical disease is treated when TSH < 0.1 with age > 65 or comorbidities, or when suppression persists at 3–6 months
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TRAb (thyrotropin-receptor antibody) StatPearls
Positive confirms Graves disease — third-generation assays reach ~97% sensitivity and 99% specificity (newer bioassays 98%/99.9%)
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Radioiodine (I-123) uptake & scan
High diffuse uptake = Graves · high patchy = toxic multinodular goiter · high solitary focus = toxic adenoma · low/absent = thyroiditis or factitious hormone intake Contraindicated in pregnancy — ultrasound takes its place
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Thyroid ultrasound with Doppler
Increased intrathyroidal blood flow suggests Graves; low flow suggests thyroiditis The tool when a radioiodine scan can’t be used (pregnancy) and for sorting amiodarone-induced subtypes
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Burch–Wartofsky Point Scale (storm) StatPearls
> 45 = thyroid storm · 25–44 supportive · < 25 unlikely — scoring fever (5 pts per 1 °F above 99 °F), CNS changes, tachycardia, atrial fibrillation, heart failure, GI dysfunction, and a precipitating factor Storm labs can look like ordinary hyperthyroidism — the diagnosis is clinical, and treatment starts before results return
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Cushing’s Syndrome
Late-night (midnight) salivary cortisol Endocrine Society 2008 Cushing syndrome diagnosis guideline, as reported by StatPearls
Fails to fall at night — the lost diurnal nadir; sensitivity and specificity 95–98% Requires at least 2 measurements evaluating early-morning and late-night levels and the preservation of a normal diurnal rhythm. It is also the best predictor of recurrence after treatment, so it reappears at every follow-up
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24-hour urinary free cortisol Endocrine Society 2008 Cushing syndrome diagnosis guideline, as reported by StatPearls
Abnormal when results are three times higher than normal free cortisol; specificity 81% Collection starts with an empty bladder — discard the first morning void. Repeat (three collections) because hypercortisolism can be episodic. Falsely low if eGFR < 60 mL/min/1.73 m², and abnormal urine volume gives false results
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1-mg overnight dexamethasone suppression test Endocrine Society 2008 Cushing syndrome diagnosis guideline, as reported by StatPearls
Give 1 mg dexamethasone at 11 PM, measure serum cortisol at 8 AM; above 1.8 µg/dL is abnormal (failure to suppress) Preparation trap: oral contraceptives and estrogens raise corticosteroid-binding globulin and cause false positives — they should be discontinued 6 weeks before. Confirm the dexamethasone was taken and absorbed with a concurrent serum dexamethasone level
Normal Suppressed cortisol < 1.8 µg/dL (50 nmol/L)
Plasma ACTH Endocrine Society 2008 Cushing syndrome diagnosis guideline, as reported by StatPearls
< 5 pg/mL is very strongly predictive of ACTH-independent disease → adrenal CT · > 20 pg/mL is highly suggestive of ACTH-dependent disease → pituitary MRI A value of 5–20 pg/mL is the grey zone and needs dynamic testing (CRH, desmopressin or metyrapone stimulation). DHEA-S moves with it: reduced in ACTH-independent disease, normal or increased in ACTH-dependent disease
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Pituitary MRI (dynamic contrast-enhanced)
Detects a corticotroph adenoma — but MRI fails to find a tumour in 40% of patients; the average detected tumour is about 6 mm A positive scan alone does not prove the source: nonfunctional microadenomas are found in 10–20% of healthy volunteers. Imaging is the third tier — screening and confirmation come first, and at least two abnormal first-tier tests are required
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Inferior petrosal sinus sampling Endocrine Society 2008 Cushing syndrome diagnosis guideline, as reported by StatPearls
Basal central-to-peripheral ACTH ratio over 3:1 with CRH administration separates pituitary from ectopic ACTH; sensitivity and specificity nearly 94% Described as "the most validated strategy" for the pituitary-versus-ectopic question, but invasive and expensive — used selectively when imaging and biochemistry disagree
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Morning serum cortisol during a glucocorticoid taper ESE / Endocrine Society 2024 joint guideline
> 300 nmol/L (10 µg/dL) = HPA axis recovered, glucocorticoid can be stopped · 150–300 nmol/L (5–10 µg/dL) = continue a physiologic dose, retest in weeks to months · < 150 nmol/L (5 µg/dL) = continue a physiologic dose, retest in a few months Draw between 8:00 and 9:00 AM after holding the glucocorticoid dose for at least 24 hours. The guideline suggests against routine dynamic testing during a taper — this single morning level is the recommended first test
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Addison’s Disease & Adrenal Crisis
Standard-dose cosyntropin (ACTH) stimulation test Endocrine Society 2016 guideline (rec 2.1)
The confirmatory test: peak cortisol below 500 nmol/L (18 µg/dL) at 30 or 60 minutes indicates adrenal insufficiency Dose is 250 µg IV. Cutoffs are assay dependent. Not performed acutely — only after stabilization, because treatment cannot wait for it
Normal Peak cortisol above 18 µg/dL is a normal response
Early-morning serum cortisol Addison Disease — StatPearls
The screening test: a low early-morning cortisol together with a high ACTH is suggestive of adrenal insufficiency A value of 18 µg/dL or above effectively excludes it; intermediate values are equivocal and require the stimulation test. In crisis this is drawn as treatment is given, not before it
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Plasma ACTH Addison Disease — StatPearls
Markedly elevated in primary adrenal insufficiency — the adrenal is failing and the pituitary is shouting at it In central (secondary or tertiary) disease the ACTH is inappropriately normal or low. This single value is what separates Addison’s disease from steroid-withdrawal insufficiency, and it is the same physiology that explains the hyperpigmentation
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Plasma renin and aldosterone (measured simultaneously) Endocrine Society 2016 guideline (rec 2.5)
In Addison’s disease: low aldosterone with elevated plasma renin activity — the mineralocorticoid axis is calling for a hormone the cortex cannot make Measured specifically to determine whether mineralocorticoid deficiency is present, which decides whether the patient needs fludrocortisone in addition to glucocorticoid. Plasma renin is also the marker used to titrate that dose long-term
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Electrolytes, glucose and renal function
The pattern to recognize: hyponatremia + hyperkalemia + hypoglycemia; hypercalcemia may occur, and creatinine may be raised from prerenal failure The hyperkalemia does not occur in secondary disease, so its presence points to a primary cause. Hyponatremia grading for context: mild 130–135, moderate 125–130, severe below 125 mEq/L, at which somnolence, confusion, seizures and cardiorespiratory collapse appear. Hyperkalemia is generally above 5.0–5.5 mEq/L
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Complete blood count
Neutropenia, lymphocytosis and eosinophilia; normocytic normochromic anemia is also described An unexplained eosinophilia in a chronically unwell, weight-losing patient is a quiet pointer toward adrenal insufficiency. TSH may also be slightly elevated — but treat the adrenal insufficiency first, because starting levothyroxine raises cortisol clearance and can precipitate crisis
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Etiology work-up Endocrine Society 2016 guideline (rec 2.6, ungraded)
Validated 21-hydroxylase antibody assay for autoimmune disease; very-long-chain fatty acids when adrenoleukodystrophy is suspected Additional studies as indicated: PPD for tuberculosis; adrenal CT or MRI for hemorrhage, calcification, infiltration, or the small glands of autoimmune disease; chest radiograph; and pituitary MRI if ACTH is inappropriately low
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SIADH & Diabetes Insipidus SIADH
Serum sodium
SIADH: below 135 mEq/L and often far lower · DI: above 146 mmol/L suggests AVP-D or AVP-R Grading in SIADH: mild 130–135, moderate 125–130, severe below 125 mEq/L. Acute is under 48 hours, chronic is over 48 hours — and that distinction, not the number, sets the correction speed. In suspected DI a low-normal or sub-135 sodium points to primary polydipsia instead
Normal 135–145 mEq/L; hypernatremia is above 145 mEq/L
Serum osmolality
SIADH: below 275 mOsm/kg · DI: 300 mOsm/kg or above is typical of AVP-D; a value at or below 280 suggests primary polydipsia Calculated as 2(Na) + (BUN)/2.8 + (glucose)/18. Step one of the hyponatremia algorithm is always to confirm the hyponatremia is genuinely hypotonic, because the isotonic and hypertonic forms are different problems entirely
Normal 285–295 mOsm/kg (a 275–295 mOsm/kg reference range is also used)
Urine osmolality
SIADH: above 100 mOsm/kg — inappropriately concentrated while the serum is dilute · DI: below 300 mOsm/kg is the hypotonic threshold The single most discriminating pair of numbers on the page. In suspected DI, 800 mOsm/kg or above rules AVP-D out ("indicates optimal plasma AVP levels and appropriate renal response"), while 300–800 indicates a partial defect needing further testing. In hyponatremia, a urine osmolality below 100 points instead to primary polydipsia, a reset osmostat, or beer potomania
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Urine sodium Schwartz and Bartter criteria, as reported by StatPearls
SIADH: above 40 mEq/L — a Schwartz and Bartter criterion In the general hyponatremia algorithm, urine sodium below 30 mEq/L means low intravascular volume, while above 30 means diuretics, renal salt wasting, or SIADH. Do not read a high urine sodium as SIADH in a patient taking a thiazide — the diuretic produces the same result by a different mechanism
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Urine specific gravity and 24-hour urine volume
Specific gravity sits at the dilute end in DI and the concentrated end in SIADH Only the normal range is established — no disorder-specific cut-point is available, so teach direction and use osmolality for the numbers. For volume, "a 24-hour urine output of less than 2.5 L is reassuring and suggests causes besides DI"
Normal 1.003–1.030 for a normal plasma osmolality
Water-deprivation test with desmopressin challenge
After deprivation, desmopressin raises urine osmolality by more than 100% in complete central DI (AVP-D) and up to 50% in partial AVP-D; in AVP-R it rises minimally or not at all A 7-hour deprivation is usually adequate; primary polydipsia may need longer. Stop the test when urine osmolality reaches the normal range, or is stable over 2–3 consecutive hourly measurements despite rising plasma osmolality, or plasma osmolality exceeds 295–300 mOsm/kg, or plasma sodium exceeds 145 mEq/L — and in children, also for a 5% loss of body weight or signs of volume depletion. The simple framing: central DI responds to desmopressin; nephrogenic DI does not
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Plasma copeptin with hypertonic saline
Copeptin levels "strongly correlate with plasma AVP levels over a wide range of osmolalities" and the sample "can remain stable for days after blood sampling" Hypertonic saline (3% saline, 1027 mOsm/L) infusion coupled with plasma copeptin measurement is described as "now being recommended by many experts in the field of DI as the preferred test to be used in place of the water deprivation test." Learn the water-deprivation test, but know it is being displaced
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Parathyroid & Calcium Disorders PHPT · hypoparathyroidism
Serum calcium (total) and ionized calcium
High in hyperparathyroidism and malignancy; low in hypoparathyroidism, after neck surgery and in hungry bone syndrome Correct for albumin: total calcium falls about 0.8 mg/dL for every 1 g/dL albumin below 4 g/dL (corrected Ca = measured + 0.8 × [4 − albumin]); "Pseudohypocalcemia occurs in hypoalbuminemia with normal ionized calcium." Hypercalcemia grades: mild 10.5–11.9 · moderate 12.0–13.9 · crisis 14.0–16.0 mg/dL
Normal Total about 8.5–10.5 mg/dL; ionized about 4.65–5.25 mg/dL — labs vary
Parathyroid hormone (intact PTH)
Primary hyperparathyroidism: high or inappropriately normal PTH with a high calcium. Hypoparathyroidism: low or inappropriately normal PTH with a low calcium. Malignancy: PTH suppressed "Diagnosis is confirmed when elevated serum calcium (total or ionized) coincides with an inappropriately high or normal PTH level measured simultaneously." Hypoparathyroidism is confirmed by a low corrected calcium with low or undetectable PTH "on 2 different serum tests at least 2 weeks apart." Ask about biotin — doses over 5 mg a day can falsely lower PTH, and "Biotin should be discontinued at least 48 hours before testing"
Normal Generally 10–65 pg/mL — varies by assay
Phosphate
Low or low-normal in primary hyperparathyroidism (PTH is phosphaturic); high in hypoparathyroidism Calcium and phosphate move in opposite directions under PTH
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Magnesium
Low magnesium causes PTH resistance and reduced secretion "Magnesium deficiency should always be corrected before treating hypocalcemia" — the calcium will not stay up until it is
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25-hydroxyvitamin D
Deficiency raises PTH and worsens hypocalcemia In the hyperparathyroidism workup, levels should be repleted "to greater than 30 ng/mL to exclude vitamin D deficiency as a secondary contributor to elevated PTH." "Hypocalcemia due to vitamin D deficiency cannot be corrected without adequate vitamin D repletion"
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Electrocardiogram
Hypercalcemia: SHORT QT, prolonged PR, widened QRS, bradycardia, heart block. Hypocalcemia: PROLONGED QTc, with a risk of torsades de pointes; hypoparathyroidism may also show T-wave alternans Place the patient on a cardiac monitor during an IV calcium bolus
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Imaging for parathyroid surgery; kidney and bone assessment
"Imaging studies for localization are reserved solely for surgical planning" — neck ultrasound and technetium-99m sestamibi. Kidney imaging for stones or nephrocalcinosis; bone density (DXA) Imaging does not make the diagnosis — the biochemistry does. Surveillance in non-operated PHPT: yearly calcium and kidney function, and a bone density test every 1 to 2 years
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Surgical criteria in asymptomatic primary hyperparathyroidism Fifth International Workshop on Primary Hyperparathyroidism (2022), as summarized by StatPearls
Any one: age under 50; serum calcium more than 1.0 mg/dL above the upper limit of normal; creatinine clearance or eGFR under 60; bone density T-score −2.5 or lower; a vertebral fracture on imaging; kidney stones or calcification; hypercalciuria above 250 mg/24 h in women or 300 mg/24 h in men. All symptomatic patients qualify "Parathyroidectomy remains the only curative treatment, with cure rates exceeding 95%"
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Pheochromocytoma PCC
Plasma free or urinary fractionated metanephrines — the first test Endocrine Society 2014 (first-line test); NCI PDQ (accuracy); StatPearls (supine draw)
Raised; in symptomatic tumours usually two to three times the upper reference limit. A mild rise is usually assay interference from drugs or other factors Endocrine Society: "initial biochemical testing for PPGLs should include measurements of plasma free or urinary fractionated metanephrines." Metabolites are measured because they "have a longer half-life" than the catecholamines. Plasma is the most sensitive (97%–99%) but less specific (85%); 24-hour urine is less sensitive (77%–90%) but more specific (98%). Draw plasma with the patient supine after at least 30 minutes lying down — StatPearls: "Guidelines recommend drawing blood with the patient in the supine position after they have been fully recumbent for at least 30 minutes before sampling," because concentrations "tend to be higher when measured in the seated position compared to the supine position, leading to reduced specificity and an increase in false positive results." Urine VMA is not the first-line test
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Test preparation — avoiding false positives
Caffeine, bananas, certain medications such as tricyclic antidepressants, and physical or emotional stress can falsely raise results MedlinePlus: "You may be asked to avoid certain foods for two to three days before the test," including caffeinated drinks and chocolate, alcohol and tobacco, bananas, citrus fruits and vanilla, and "to avoid stress and vigorous exercise before your test" — but "don’t stop taking any medicines unless your provider tells you to"
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24-hour urine collection
All urine for 24 hours, refrigerated or kept on ice Discard the first void and note the time; collect everything for the next 24 hours; "store the urine container in a refrigerator or cooler with ice"; at 24 hours "try to urinate if you can. This is the last urine collection for the test."
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CT or MRI — only after the biochemistry is positive Endocrine Society (2014)
Localises the tumour "Once the biochemical diagnosis of a catecholamine-secreting tumor is confirmed, localization studies should be performed." CT is suggested first; MRI for metastatic disease or when radiation must be limited; MIBG for metastatic disease
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No biopsy and no provocative testing
Fine-needle aspiration of the tumour is a crisis trigger "Provocative testing (e.g., using glucagon) can be dangerous, adds no value to other current testing methods, and is not recommended."
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Genetic testing
Offered to every patient Endocrine Society: "We recommend consideration of genetic testing in all patients." NCI: every patient "should first undergo risk evaluation for a hereditary syndrome by a certified genetic counselor"
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Obesity & Metabolic Syndrome Overweight and obesity
BMI USPSTF
Overweight 25–29.9; obesity ≥ 30 (class 1 30.0–34.9, class 2 35.0–39.9, class 3 ≥ 40) USPSTF categories, "calculated as weight in kilograms divided by height in meters squared."
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Waist circumference NHLBI
> 40 in (men) or > 35 in (women) StatPearls: "Every patient presenting for the evaluation should have waist circumference measured." NHLBI: providers may use different values "depending on your race and ethnicity."
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Blood pressure
≥ 130/85 mm Hg (consistently) NHLBI and StatPearls criterion.
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Fasting glucose and hemoglobin A1c NHLBI
Fasting glucose ≥ 100 mg/dL (100–125 prediabetes; ≥ 126 may be diabetes) StatPearls: "The initial blood work should include fasting blood glucose and hemoglobin A1c to screen for insulin resistance and diabetes mellitus."
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Lipid panel
Triglycerides above 150 mg/dL; HDL < 40 (men) or < 50 (women) NHLBI: triglycerides "consistently more than 150 mg/dL"; StatPearls: "150 mg/dL or greater." A basic metabolic panel checks kidney function.
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Selected tests
CRP, liver tests, thyroid studies, uric acid StatPearls: these "can be considered in a selected group of patients to evaluate associated disorders"; hypothyroidism is "a close differential of metabolic syndrome."
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After bariatric surgery — nutrition labs
B vitamins, iron, trace elements; yearly CBC, BMP, liver tests, lipids StatPearls: "Nutritional parameters should be monitored regularly after bariatric surgery, including B vitamins, iron and trace elements. General labwork should be followed annually." StatPearls (Bariatric Malnutrition): "lifelong postoperative monitoring is essential to detect and prevent deficiencies and enable early intervention."
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Digestive / GI

GI Bleed, Peptic Ulcer Disease & Gastritis PUD
EGD (esophagogastroduodenoscopy) ACG 2021 · StatPearls
The gold standard — sensitivity and specificity up to 90%; in UGIB, performed within 24 hours of presentation (12 h if variceal bleeding is suspected) Indicated for anyone with alarm symptoms regardless of age and for new dyspepsia over 50. It is diagnosis and treatment in one — see endoscopic hemostasis below. Every gastric ulcer seen gets biopsied to exclude gastritis, H. pylori, and malignancy
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H. pylori testing StatPearls
Urea breath test and stool antigen are the preferred noninvasive tests (accuracy similar to invasive methods); biopsy-based testing when EGD is done anyway Serology (IgG) is not recommended — it cannot distinguish active from past infection. Test ≥ 2 weeks after stopping the PPI and ≥ 4 weeks after antibiotics, or the result may be falsely negative
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Hemoglobin ACG 2021 · StatPearls
Falls with blood loss. Restrictive transfusion strategy: transfuse at Hgb < 7 g/dL (< 8 g/dL with cardiovascular disease) Send the type and crossmatch early — antibody identification and crossmatching can take hours; in emergencies uncrossmatched group O red cells may be issued
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BUN-to-creatinine ratio
A ratio > 30 suggests an upper GI source A cheap localization clue that arrives long before the endoscope does
Normal Ratio well below 30 with normal renal function
Orthostatic vital signs StatPearls
Positive when SBP drops ≥ 20 mm Hg or DBP drops ≥ 10 mm Hg within 3 minutes of standing; a compensatory HR rise > 15 bpm points to volume depletion Measure after at least 5 minutes supine, then at 1, 2, and 3 minutes standing — and stand by the patient: lightheadedness, syncope, and falls are the symptoms
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Glasgow-Blatchford score ACG 2021 · StatPearls
Score 0–1 identifies very-low-risk patients who may be discharged from the ED; ≥ 6 carries over 50% risk of needing intervention Risk stratification done before endoscopy — it steers disposition, not diagnosis
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Cirrhosis & Its Complications
AST & ALT
Usually only mildly–moderately elevated, with the ratio reversing to AST > ALT as cirrhosis develops Normal enzymes do not rule out cirrhosis — a burned-out liver has few hepatocytes left to leak enzymes
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Albumin · PT/INR · bilirubin
Albumin low, PT/INR prolonged, bilirubin elevated — the synthetic-function trio These three (not AST/ALT) are the true indicators of hepatic synthetic function, and all three feed the Child-Pugh score
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CBC
Thrombocytopenia and leukopenia (splenic sequestration); anemia — macrocytic in alcohol-associated disease During an active bleed, hemoglobin can read deceptively normal for 6–24 hours until the blood volume re-equilibrates
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Ascitic fluid analysis (paracentesis)
SAAG ≥ 1.1 g/dL = portal-hypertensive ascites (97% accuracy) · PMN ≥ 250/mm³ = spontaneous bacterial peritonitis New-onset ascites and every hospitalized patient with ascites warrant a diagnostic paracentesis
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Ammonia
Usually elevated in encephalopathy — but not definitive; a normal level has high negative predictive value The sample must be tested within 1 hour and kept cool; treat the patient’s mental status, not the number. CT/MRI rule out bleed, stroke, or lesion
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Child-Pugh & MELD scores MELD 3.0 (US transplant allocation, July 2023)
Child-Pugh (albumin, bilirubin, PT, ascites, encephalopathy): A = 5–6 well-compensated · B = 7–9 · C = 10–15 decompensated. MELD (bilirubin, creatinine, INR, sodium; the US has used MELD 3.0, which adds sex and albumin, since July 2023) predicts 3-month mortality MELD 3.0 sets US liver-transplant waitlist priority; Child-Pugh class drives complication risk — variceal-bleed in-hospital mortality runs 0% in class A vs 32% in class C
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Pancreatitis (Acute & Chronic)
Serum lipase ACG 2024
> 3× the upper limit of normal — one of the 2-of-3 diagnostic criteria (with characteristic pain and imaging findings; revised Atlanta, restated by ACG 2024) Lipase is the preferred enzyme — more specific and stays elevated longer than amylase. Amylase is mostly non-pancreatic (salivary glands 55–60%), normalizes in 3–7 days (normal ~30–110 U/L), and rises in many non-pancreatic conditions; ordering both adds no sensitivity or specificity
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BUN & hematocrit ACG 2024
Rising values = intravascular volume depletion from third-spacing — both correlate with poorer outcomes These are your fluid-resuscitation report card: the goal is a falling BUN with urine output > 0.5 mL/kg/h. Reassess within 6 h of starting fluids and over the next 24–48 h
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Calcium & triglycerides ACG 2024
Calcium may fall (saponification of necrotic fat sequesters it); triglycerides > 1,000 mg/dL implicate hypertriglyceridemia as the cause Both belong to the etiologic bloodwork alongside the liver profile. A falling calcium is a complication in motion — pair the number with Chvostek/Trousseau checks
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Transabdominal ultrasound ACG 2024, Rec 1
Performed in all acute pancreatitis patients to look for gallstones (biliary pancreatitis); repeat if inconclusive Finding stones changes the plan: index-admission cholecystectomy, and urgent ERCP if cholangitis develops
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BISAP score (severity prediction) StatPearls / ACG 2024
1 point each: BUN > 25 mg/dL · Impaired mental status (GCS < 15) · SIRS · Age > 60 · Pleural effusion — 0–2 → mortality < 2%; 3–5 → mortality > 15% SIRS = ≥ 2 of: HR > 90 · RR > 20 (or PaCO₂ < 32) · T > 38 °C or < 36 °C · WBC > 12,000 or < 4,000. SIRS or organ failure → the patient belongs on a monitored bed
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Fecal elastase-1 (chronic disease)
< 200 μg/g stool = abnormal · < 100 μg/g = pancreatic insufficiency Chronic pancreatitis is an imaging-plus-function diagnosis: CT shows calcifications — the hallmark sign — while amylase/lipase are not the mainstay; FE-1 and stool fat quantify what exocrine capacity remains
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Bowel Obstruction & Ileus SBO
CT abdomen (IV contrast) StatPearls
The gold standard for SBO: dilated loops, a transition point, bowel-wall thickening, mesenteric stranding, cause and perforation signs. Ileus shows diffuse dilation with no transition point The transition point is the discriminator between obstruction and ileus. IV contrast is useful; oral contrast is contraindicated in LBO
Normal No dilated loops; no transition point
Upright abdominal X-ray StatPearls
Dilated small-bowel loops with air-fluid levels in a step-ladder pattern; absence of colon gas suggests complete SBO; small-bowel diameter > 6 cm indicates severe obstruction. LBO: dilated colon, no gas in the rectum Sensitivity only 50–80% — a normal film does not exclude obstruction. Free air under the diaphragm = perforation. Repeated in series to track distension over time
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CBC + lactate StatPearls
Leukocytosis with infection, inflammation, or strangulation; elevated lactate suggests tissue hypoxia — ischemia or necrosis Leukocytosis and acidosis are among the sourced surgical-triggers; trend them serially, not once
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Electrolytes + ABG StatPearls
Hyponatremia, hypokalemia, and metabolic alkalosis from vomiting and NG losses; lactic acidosis instead points to bowel ischemia or infarction Alkalosis is the expected derangement — acidosis in this patient is a red flag, not a lab quirk
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Ultrasound StatPearls
Dilated small-bowel loop > 3 cm or edematous wall > 3 mm suggests obstruction; a visualized transition point is specific for obstruction
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Water-soluble contrast study (e.g. Gastrografin) StatPearls
Contrast that reaches the colon predicts nonoperative success — and the agent itself can help resolve adhesional obstruction Both prognostic and therapeutic in adhesive SBO; as an enema, it reliably distinguishes mechanical LBO from pseudo-obstruction
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Appendicitis & Peritonitis
WBC with differential StatPearls
Leukocytosis in ~two-thirds of patients, most > 10,000 cells/mm³, often with a left shift; ≥ 17,000 cells/mm³ is associated with complicated appendicitis (gangrene, perforation) In pregnancy the physiologic leukocytosis (up to 16,900 cells/mm³) makes the WBC unreliable — don’t let a “normal-for-pregnancy” count falsely reassure
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CRP StatPearls
Elevated; WBC + CRP together help distinguish complicated from uncomplicated disease A normal WBC and normal CRP together have a high negative predictive value — the useful rule-out combination
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CT abdomen/pelvis with IV contrast (adults) WSES 2020
> 95% accurate: appendix outer diameter > 6 mm, wall thickening > 2–3 mm, periappendiceal fat stranding, wall enhancement, appendicolith Contrast-enhanced low-dose CT is recommended over standard-dose; avoided in pregnancy
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Ultrasound (first-line in children & pregnancy) WSES 2020
Noncompressible appendix > 6 mm is diagnostic; diameter < 5 mm excludes appendicitis No ionizing radiation — POCUS is the first-line tool in children [Strong]; graded-compression US is preferred initially in pregnancy, with MRI (sensitivity 91.8%, specificity 97.9%) when US is inconclusive
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Clinical scores (AIR · AAS · Alvarado · PAS) WSES 2020
Modified Alvarado ≥ 7 significantly associated with appendicitis; Pediatric Appendicitis Score ≥ 6 suggestive WSES 2020 recommends the AIR and AAS scores as clinical predictors and discourages Alvarado for confirmation (insufficient specificity); Alvarado is also unreliable for complicated-vs-uncomplicated in elderly patients
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Upright chest X-ray (suspected perforation) StatPearls
Free air under the diaphragm (pneumoperitoneum) — visible in 50–70% of perforations on upright/lateral decubitus films CT is the gold standard for small volumes of free air; with peritonitis add lactate (end-organ perfusion) and blood cultures
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Inflammatory Bowel Disease IBD
Colonoscopy with biopsy (± ileoscopy) ACG 2019 / AGA 2021 / ECCO 2023 / BSG 2025 surveillance intervals as reported by a 2026 PMC review
The diagnostic anchor. UC: continuous, circumferential loss of vascular pattern, granularity, friability, ulceration from the rectum upward, pseudopolyps; biopsy crypt abscesses, no granulomas. CD: skip lesions, cobblestoning, rectal sparing; biopsy noncaseating granulomas (up to 33%) Multiple biopsies are needed and no single test makes the diagnosis (clinical + radiologic + endoscopic + histologic). Contraindicated in toxic megacolon (perforation risk); bowel prep and colonoscopy in a severely inflamed colon are toxic-megacolon precipitants. Capsule endoscopy: caution with known strictures (capsule retention). Surveillance colonoscopy starts 8–10 years after onset, then every 1–5 years by risk; yearly with PSC
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UC severity classification (NIDDK symptom grading; Truelove & Witts for acute severe UC) NIDDK (stool/blood grading); Truelove–Witts as tabulated by a 2025 PMC review
Mild: < 4 stools/day, blood only sometimes. Severe: > 6 stools/day with blood most of the time. Fulminant: > 10 bloody stools/day. Acute severe UC: > 6 bloody stools/day + ≥ 1 of T > 37.8 °C, pulse > 90, Hgb < 10.5 g/dL, ESR > 30 mm/h or CRP > 30 mg/L Stool charting over 24 h is how the nurse feeds this scale. On day 3 of IV steroids, ≥ 8 stools/day or 3–8 stools with CRP ≥ 45 mg/L (Oxford criteria) predicts ~85% colectomy risk → rescue infliximab/cyclosporine or surgery. The Mayo score (stool frequency, bleeding, endoscopy, physician global; 0–12) tracks activity over time
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Fecal calprotectin AGA 2023 CD monitoring as reported by StatPearls
Elevated in active IBD; < 150 µg/g (with CRP < 5 mg/L) = minimal or absent inflammation; < 50 µg/g excludes post-surgical CD recurrence A neutrophil-derived stool protein — the rule-out test that separates IBD from IBS (only IBD is inflammatory). Nonspecific: also raised by infection, NSAIDs, and cancer. Used with CRP every 6–12 months in remission and every 2–4 months when active
Normal Low; < 1% of patients with a low value have IBD
CRP & ESR
Both rise with active inflammation, especially in an acute flare; CRP > 30 mg/L or ESR > 30 mm/h is a severity criterion; CD treatment target CRP < 5 mg/L Trend them against the stool chart — a falling CRP with fewer bloody stools means the steroids are working; a CRP ≥ 45 mg/L on day 3 is the escalation trigger
Normal CRP < 0.3 mg/dL (3 mg/L) · ESR < 15 mm/h (men < 50), < 20 (women < 50); higher limits > 50 y
CBC — hemoglobin & WBC
Anemia (blood loss, iron, B12, chronic disease): Hgb < 10.5 g/dL marks acute severe UC, transfusion requirement marks fulminant disease. Leukocytosis in flares; WBC > 10,500/µL with left shift is a Jalan toxic-megacolon criterion Monitor Hgb/iron every 6–12 months in remission and every 3 months in active disease; anemia predicts more hospitalization and surgery
Normal Hgb 13.8–17.2 g/dL (men), 12.1–15.1 g/dL (women) · WBC 4,500–11,000/µL
Albumin & electrolytes (potassium)
Albumin low (< 3.4 g/dL) from malabsorption and inflammation — part of the "severe" UC picture and a mortality risk factor in toxic megacolon. Potassium low (< 3.7 mEq/L) from diarrhea and vomiting — a toxic-megacolon precipitant and a typical TM lab Replace electrolytes IV "based on laboratory results"; labs run twice daily initially in toxic megacolon, then daily. Metabolic acidosis suggests colonic ischemia
Normal Albumin 3.4–5.4 g/dL · K⁺ 3.7–5.2 mEq/L
Stool studies — culture, ova & parasites, C. difficile toxin (+ CMV biopsies in ASUC)
Must be negative before a flare is labeled a flare — colonic infection is clinically indistinguishable from UC Sent on every flare: C. difficile and CMV both mimic and precipitate severe colitis and toxic megacolon. pANCA (UC) and ASCA (CD) serologies are an adjunct only — not routinely indicated
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Imaging — plain film, CT, MR enterography
Toxic megacolon: colon > 6 cm (transverse/ascending), air-fluid levels, loss of haustral markings; CT wall thickening. CD: CT/MRE shows abscesses, strictures, fistulae (MRI best for fistulizing disease and preferred in children); small-bowel "string sign" of stricture Plain radiographs when obstruction is suspected; abdominal imaging is mandatory in acute severe UC to exclude megacolon and perforation, repeated twice daily initially in TM. Radiology is not needed to diagnose uncomplicated UC
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GERD & Hiatal Hernia GERD
Empiric PPI trial (the diagnostic that is also the treatment) ACG 2022
Heartburn + regurgitation without alarm features → 8 weeks of once-daily PPI taken before a meal; a response supports the diagnosis Pooled sensitivity ~78% but specificity only 54% — a response does not prove GERD, and a non-response is not the end of the workup. Never the first step when chest pain is the complaint (rule out the heart) or when alarm features are present (scope first)
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Upper endoscopy (EGD) with Los Angeles grading ACG 2022 · LA classification
Erosive esophagitis graded LA-A (breaks < 5 mm) · LA-B (> 5 mm, not bridging folds) · LA-C (bridging folds, < 75% of circumference) · LA-D (> 75% of circumference); or Barrett’s salmon-colored mucosa; or a normal study (NERD) First test for dysphagia, odynophagia, weight loss, GI bleeding, anemia, vomiting, and for age ≥ 50 with reflux > 5 years, overweight, or ≥ 3 Barrett’s risk factors. Best done off PPIs for 2–4 weeks (antacids allowed) to raise erosive yield and exclude eosinophilic esophagitis. LA-C is virtually always diagnostic; LA-C/D need a repeat scope after 8–10 weeks of PPI
Normal Intact pale-pink squamous mucosa; LA-A alone is not reliably different from normal
Ambulatory reflux monitoring (24-h catheter pH, 48–96-h wireless capsule, or impedance-pH) ACG 2020 physiologic testing (Lyon consensus; thresholds unchanged in Lyon 2.0, 2024)
Acid exposure time (AET, pH < 4) > 6% = pathologic · 4–6% borderline · < 4% physiologic; symptom index > 50% or symptom-association probability > 95% ties symptoms to reflux The only test that quantifies acid reflux. Done off PPI (stopped ≥ 7 days) when GERD is suspected but unproven and the scope was normal; done on twice-daily PPI (impedance-pH, which also catches non-acid reflux) for proven GERD with persistent symptoms. Teach: fast 4–6 hours before the probe is placed, medication holds only as the provider directs, keep a symptom/meal/position diary, live normally during the recording; the capsule passes on its own in 4–10 days
Normal AET < 4% of the recording
High-resolution esophageal manometry ACG 2022
A weak LES or ineffective motility may be seen — but manometry is not alone a diagnostic test for GERD; it is required before any antireflux surgery to exclude achalasia and absent contractility Operating on a mistaken diagnosis "can result in devastating dysphagia." Also locates the LES for pH-catheter placement and detects a hiatal hernia by the gap between LES and crural diaphragm. Prep: fast ≥ 6 h; hold CCBs, nitrates, opioids, sedatives, H2RAs, PPIs, and caffeine ≥ 24 h as directed
Normal Integrated relaxation pressure < 15 mm Hg; resting LES 15–30 mm Hg
Barium esophagram / upper-GI series ACG 2022 (GERD) · StatPearls (hernia)
The gold standard for defining a hiatal hernia — size, type, location — and shows strictures and rings; not recommended as a test for GERD itself Only ~50% of patients with barium reflux have abnormal pH monitoring, so barium reflux neither confirms nor excludes GERD. Prep: fast after midnight; no smoking, gum, or candy that coat the throat. Often obtained on post-op day 1 after fundoplication
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Chest X-ray / CT
A retrocardiac air-fluid level = stomach in the chest; volvulus shows a spherical stomach with a double air-fluid level above the diaphragm Often the incidental first clue to a large hernia; CT defines large or recurrent paraesophageal hernias and plans volvulus surgery. In a patient with the Borchardt triad, this film is the emergency confirmation, not a routine order
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ECG + high-sensitivity troponin (when chest pain is the complaint)
Must be normal/negative before any GI attribution; ECG interpretation is the cornerstone, integrated with symptom timing and troponin Cardiac labs are ordered to rule out MI "when atypical chest pain is present"; GERD is a diagnosis made after the heart is cleared, never instead of checking it. Relief from an antacid or nitroglycerin does not discriminate
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CBC, ferritin & stool occult blood
Microcytic, hypochromic anemia with low ferritin and positive occult blood in erosive disease or Cameron lesions; WBC and lactate rise if a strangulated hernia turns septic Anemia is an alarm feature that reroutes the patient to endoscopy; Cameron lesions hide in the hernia sac and are often missed on a first EGD, so a repeat exam is common
Normal Normal indices; occult blood negative
Viral Hepatitis
ALT / AST StatPearls; AASLD 2018 (treatment threshold)
Markedly elevated in acute infection — up to a 10- to 100-fold rise in HAV, where ALT runs higher than in other viral hepatitis (hepatocellular pattern) Magnitude ≠ severity — a huge ALT with a normal INR and clear mind is expected; a falling ALT with a rising INR is failure, not recovery. ALT more than 2× the upper limit of normal (AASLD 2018 uses 35 U/L men / 25 U/L women) plus a high HBV DNA is the chronic-HBV treatment trigger
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Bilirubin (total / conjugated) StatPearls
Rises after the transaminases; conjugated fraction elevated in the icteric phase; jaundice visible above ~2–3 mg/dL; > 10 mg/dL is a severity trigger for antiviral therapy in acute HBV Track the trend, not the single value — worsening jaundice with rising bilirubin is one of the heralding cues of acute liver failure
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PT / INR (+ albumin, glucose, ammonia) StatPearls (Acute Liver Failure)
Normal unless severe — INR ≥ 1.5 with encephalopathy defines acute liver failure; acute-HBV antiviral thresholds quote INR > 1.5–1.6 The severity marker of the whole page. In ALF, correct coagulopathy only for active bleeding or before invasive procedures — the INR is the prognostic signal you do not want to erase. ALF adds hypoglycemia, elevated ammonia, lactate/metabolic acidosis, and a rising creatinine; albumin and PT track synthetic function in chronic disease
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HAV serology (IgM / IgG anti-HAV)
IgM anti-HAV = acute infection (positive 4–6 months); IgG anti-HAV = past infection or vaccination = lifelong immunity IgM turns positive before IgG; the antibody type separates current infection from past infection or vaccination
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HBV serology (triple panel ± HBeAg, HBV DNA) CDC 2023 / ACIP 2018
Acute: HBsAg +, IgM anti-HBc +, anti-HBs −. Chronic: HBsAg + > 6 months, total anti-HBc +, IgM anti-HBc −. Resolved: HBsAg −, anti-HBs +, anti-HBc +. Immune from vaccine: anti-HBs + alone. Susceptible: all negative. Window period: HBsAg gone, anti-HBs not yet present — IgM anti-HBc may be the only positive marker HBsAg = current infection (first marker detected); anti-HBs = immunity; total anti-HBc = past or present infection; IgM anti-HBc = acute; HBeAg = high infectivity/viral load; HBV DNA = replication. Vaccination makes anti-HBs only — an anti-HBc tells you the person met the real virus. Protective anti-HBs = ≥ 10 mIU/mL
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HCV antibody → reflex HCV RNA CDC 2020
Anti-HCV reactive → HCV RNA (NAT) confirms current infection; anti-HCV + with RNA − = resolved infection or false positive, not current disease Antibody appears 4–10 weeks after exposure, RNA at 1–2 weeks. Antibody stays positive for life — including after cure — so post-treatment monitoring and re-testing after reinfection use RNA. Cure (SVR) = no detectable RNA 12 weeks after finishing therapy. Staging follows: viral load, genotype, and fibrosis by APRI/FIB-4 or transient elastography (FibroScan), preferred over biopsy
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HDV and HEV testing
HDV: HBsAg must be positive (no HBsAg = no HDV) + anti-HDV; HDV RNA by RT-PCR is the most sensitive test; IgM anti-HBc present = coinfection, absent = superinfection. HEV: IgM anti-HEV for acute infection; HEV RNA in serum or stool is definitive and the cornerstone in the immunocompromised Order HDV testing on any chronic-HBV patient with a sudden severe hepatitis — superinfection is the classic cause of an unexplained flare
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Anti-HBs after vaccination (post-vaccination serology) ACIP 2018
≥ 10 mIU/mL = immune (documented responder); < 10 → revaccinate and retest Drawn 1–2 months after the final dose for health care personnel and dialysis patients; for infants of HBsAg-positive mothers at 9–12 months, not earlier, to avoid detecting passive anti-HBs from HBIG
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Cholecystitis & Cholelithiasis
Right-upper-quadrant ultrasound (first-line) WSES 2020
Stones (detects stones as small as 2 mm; 90–95% accurate) plus the acute-cholecystitis signs: wall thickened > 3 mm, wall edema, pericholecystic fluid, sonographic Murphy’s sign (pain under the probe); a dilated CBD > 6 mm flags a duct stone The preferred initial test (WSES), drawn alongside liver function tests — but sensitivity is only 81% and specificity 83% for acute cholecystitis, so a negative scan does not close the case. TG18 (as reported by EClinicalMedicine 2024) sets its imaging threshold at 3.5 mm. Ultrasound sees the dilated duct with 90% accuracy but the stone inside it only 15–40% of the time
Normal Wall ≤ 3 mm · no pericholecystic fluid · CBD ≤ 6 mm
HIDA scan (cholescintigraphy) WSES 2020
Gallbladder fails to fill with tracer = cystic-duct obstruction — close to 100% accurate for acute cholecystitis; with CCK stimulation, ejection fraction < 35% = hypokinetic gallbladder (biliary dyskinesia / acalculous work-up) Second-line when ultrasound is equivocal — WSES: the highest sensitivity and specificity of the second-line tests. Prep is a nursing job: NPO for at least 3–4 h but not > 24 h (prolonged fasting concentrates bile → false positive; sincalide is given if fasting ran long), and hold opioids ≥ 6 h — they contract the sphincter of Oddi and mimic obstruction. Radiation ≈ 3–4 mSv
Normal Gallbladder visualizes · ejection fraction ≥ 35%
CBC, CRP & liver panel Tokyo Guidelines 2018 (as reported by J Clin Med 2023) · WSES 2020 · ASGE 2019
Leukocytosis and ↑ CRP in acute cholecystitis (WBC > 18,000 = TG18 Grade II); bilirubin > 2 mg/dL suggests a CBD stone, > 3–4 mg/dL strongly; cholestatic ↑ ALP, ↑ GGT, ↑ transaminases when the duct is obstructed Labs can be normal in chronic disease even with a severely diseased gallbladder. Never use bilirubin or LFTs as the only evidence of a duct stone (WSES). ASGE 2019 risk tiers: abnormal LFTs, age > 55, or a dilated CBD on ultrasound = intermediate → MRCP, EUS or intraoperative cholangiography first; a duct stone on imaging, clinical cholangitis, or bilirubin > 4 mg/dL with a dilated CBD (> 6 mm with gallbladder in place) = high → straight to duct clearance
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Amylase & lipase
Normal in uncomplicated cholecystitis — elevated = gallstone pancreatitis (stone at the ampulla) Drawn on every admission "to rule out pancreatitis"; a positive result reroutes the plan and the surgical timing (see Pancreatitis)
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MRCP → EUS → ERCP (duct stones) ASGE 2019 · StatPearls
MRCP: 92% sensitivity, 100% specificity for CBD stones — a highly accurate non-invasive test (WSES pooled sensitivity 93%, specificity 96%); ERCP sees the stone and removes it (sphincterotomy + basket/snare extraction) When suspicion of a duct stone persists despite a negative ultrasound, MRCP is next (92% sensitive, 100% specific); ASGE 2019 suggests EUS or MRCP for intermediate-risk patients. ERCP is reserved for treatment because of ≈ 10% post-procedure pancreatitis (rectal indomethacin lowers the risk); if ERCP fails, a stent is a temporary bridge only
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CT abdomen (contrast) WSES 2020
Distension, wall thickening, pericholecystic fluid, radio-opaque stones; gas in the wall or lumen = emphysematous cholecystitis; abscess, perforation; gallstone ileus shows the Rigler triad (pneumobilia + small-bowel obstruction + ectopic stone, 93% sensitive) WSES: accuracy for uncomplicated cholecystitis is poor, so CT is the test for suspected gangrenous, emphysematous or perforated disease and cholangitis complications — though it is often ordered first in the ED. Only ≈ 10% of gallstones show on plain radiographs
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TG18 diagnostic criteria & severity grade Tokyo Guidelines 2018 (as reported by J Clin Med 2023 & StatPearls)
Cholecystitis: A local signs (Murphy’s sign, RUQ pain/mass/tenderness) + B systemic signs (fever, ↑ CRP, ↑ WBC) = suspected; + C characteristic imaging = definite. Cholangitis: A systemic inflammation + B cholestasis (bilirubin ≥ 2 mg/dL or abnormal ALP/GGT/transaminases) + C duct dilation or a visible cause on imaging Grade I mild · Grade II moderate (cholecystitis: WBC > 18,000, palpable mass, symptoms > 72 h, marked local inflammation; cholangitis: two of WBC > 12,000 or < 4,000, fever ≥ 39 °C, age ≥ 75, bilirubin ≥ 5 mg/dL, hypoalbuminemia) · Grade III = any organ dysfunction — the nurse’s sepsis checklist. TG18 cholangitis criteria: sensitivity 100%, specificity 87.4%, versus Charcot’s 26.4%
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Blood cultures, PT/INR & platelets (cholangitis/sepsis work-up) Tokyo Guidelines 2018 (as reported by J Clin Med 2023)
Bacteremia with gram-negatives or anaerobes; prolonged PT/INR from vitamin-K malabsorption; INR > 1.5 or platelets < 100,000 = TG18 Grade III organ dysfunction Anticipate parenteral vitamin K before ERCP or surgery and bleeding precautions while the patient is jaundiced. Bacteremia lifts severe-biliary-infection mortality from 1–6% to 10–20%
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Diverticular Disease Diverticulosis
CT abdomen and pelvis with IV contrast AGA Clinical Practice Update (2021)
Colonic wall thickening and fat stranding = diverticulitis; a phlegmon, abscess, free air or fistula = complicated diverticulitis The gold standard (98%–99% sensitivity, 99%–100% specificity). The AGA advises CT to confirm a first, unconfirmed episode and to look for complications in severe presentations, because clinical suspicion alone is right in only 40–65%
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White blood cell count and C-reactive protein AGA Clinical Practice Update (2021)
Leukocytosis and raised inflammatory markers, most often CRP A CRP above 140 mg/L or a raised baseline white cell count is one of the AGA’s reasons to give antibiotics in uncomplicated disease
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Ultrasound
An alternative initial test WSES suggests ultrasound in initial evaluation "where it is performed by an expert operator"
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Colonoscopy — timing matters AGA Clinical Practice Update (2021)
Contraindicated during the acute episode "due to the risk of intestinal perforation." Advised 6 to 8 weeks later (or when symptoms have fully resolved, whichever is longer) after complicated diverticulitis and after a first uncomplicated episode, unless a high-quality colonoscopy was done within the past year Cancer can mimic diverticulitis — colon cancer was found in 7.9% after complicated versus 1.3% after uncomplicated episodes. For bleeding, colonoscopy in a prepped colon is the best test to find the source
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Modified Hinchey classification WSES 2020 guideline
0 mild · 1a pericolic inflammation · 1b pericolic abscess · 2 pelvic or distant abscess · 3 generalized purulent peritonitis · 4 fecal peritonitis Hinchey III and IV require surgery for source control
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Colorectal Cancer CRC
Colonoscopy with biopsy
The tumor is seen, biopsied and tattooed — "Ultimately, a colonoscopy is required for a tissue diagnosis" Sensitivity "about 94.7% if performed by an experienced operator and with good bowel preparation"; "Around 2% to 6% of lesions may be missed, especially right-sided, sessile, and flat lesions." Sedation is almost always used, so the patient needs someone to accompany them. Generally avoided if bowel perforation is a concern
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Stool tests — gFOBT, FIT, stool DNA-FIT (screening) USPSTF 2021
Abnormal = colonoscopy. A stool test is a screen, not a diagnosis gFOBT false positives: "the presence of dietary heme from red meat, peroxidase from some plants, and anti-oxidants like vitamin C or E can lead to false positives." FIT: "Dietary and medication restrictions prior to the test aren’t required." Samples should reach the lab within 24 hours; don’t rehydrate them
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Carcinoembryonic antigen (CEA)
Measured at baseline; high levels "correlate with poor prognosis," and levels after treatment "are useful in detecting disease recurrence" Not a screening test — "A CEA level is not a valuable screening test for colorectal cancer because of the large number of false-positive and false-negative reports." Pre-operative CEA is expected to normalize after resection, with serial assays at follow-up; NCI adds that CEA alone is not recommended for routine monitoring of treatment response
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CBC, iron studies, metabolic panel, liver function, coagulation
Iron-deficiency anemia from chronic bleeding; liver tests for metastatic spread StatPearls’ routine baseline workup for colon cancer
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CT chest, abdomen and pelvis
Staging — nodes and distant metastases, most often liver "recommended for all patients diagnosed with colon cancer"; "A positron emission tomography-CT scan is not routinely indicated." Rectal cancer adds MRI or transrectal ultrasound for local extent and nodes
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Pathology — lymph nodes and MMR/MSI status AJCC/NCI panel (nodes) · NCCN, via StatPearls (MMR/MSI)
At least 12 lymph nodes examined to confirm no nodal involvement; universal MMR/MSI testing Stage III = lymph node involvement; stage IV = distant metastases. MMR/MSI status affects about 15% to 20% of sporadic colorectal cancers; KRAS, NRAS, HER2 and BRAF testing for nonresectable metastatic disease
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Celiac Disease & Malabsorption Celiac sprue
Tissue transglutaminase IgA (tTG-IgA) with total IgA ACG 2023, via StatPearls
Elevated tTG-IgA in untreated celiac disease; the first test Must be done while still eating gluten. "A negative tTG-IgA result has a high negative predictive value." Total IgA is checked at the same time because 2% to 3% of people with celiac disease are IgA deficient; "In patients with confirmed IgA deficiency, IgG-based testing is recommended." Antibodies "are higher in untreated celiac disease but typically return to normal after treatment"
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Endomysial antibody (EMA)
Positive in celiac disease "Anti-TTG is considered the most sensitive test, while anti-EMA offers the highest specificity"
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Upper endoscopy with duodenal biopsies ACG 2023
Villous atrophy with crypt hyperplasia — villus-to-crypt ratio often below 2:1 (normal about 3:1) "Intestinal biopsy is required in most patients to confirm the diagnosis." Take 1 to 2 biopsies from the duodenal bulb and 4 from the distal duodenum. A nonbiopsy route is suggested only for selected children
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HLA-DQ2 / DQ8 genetic test
Present in almost everyone with celiac disease — but also in about 30% of the population Rules out, not in: "A negative HLA test rules out celiac disease with a high degree of certainty"
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Skin biopsy (dermatitis herpetiformis)
Granular IgA deposits at the dermal papillae on direct immunofluorescence (about 92% of cases) Biopsy "perilesional skin—normal-appearing skin adjacent to a lesion"
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Quantitative fecal fat — 72-hour stool collection
More than 21 g of fat over 72 hours indicates steatorrhea The gold standard for steatorrhea. The patient eats 100 g of fat a day, starting 3 to 5 days before the collection and continuing through the 72 hours. Fecal elastase is low in pancreatic insufficiency
Normal 2 to 7 g over 24 hours
Deficiency screen — CBC, iron studies, B12, folate, vitamin D, albumin, electrolytes, magnesium, zinc
Iron-deficiency or megaloblastic anemia; low vitamins, minerals and protein; electrolyte disturbances Bone mineral density testing may be ordered to check for osteoporosis
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Clostridioides difficile Infection C. diff
Who to test SHEA/IDSA/APIC 2022
3 or more unexplained, new-onset, unformed stools in 24 hours Compendium: "only test patients with clinically significant diarrhea." Rule out laxatives, stool softeners and new tube feeds first. Do not test patients without significant diarrhea, those tested in the prior 7 days, or children under 1 year. Send only unformed stool.
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Stool specimen handling CDC
To the lab promptly, or refrigerated CDC: "The toxin degrades at room temperature and might be undetectable within two hours of stool specimen collection." Delays cause false negatives.
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PCR (nucleic acid amplification) test
Positive for a toxin-producing strain Same-day, highly sensitive and specific — but can be positive in colonized people without infection, leading to over-diagnosis. A negative NAAT has high negative predictive value; the patient can come off contact precautions.
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GDH antigen and toxin tests (two-step testing)
Antigen positive + toxin positive supports CDI CDC: antigen results alone are nonspecific, so they are combined with toxin, PCR or culture testing. StatPearls: a single test is not informative enough, so a 2-step sequential approach is used.
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CBC, albumin, creatinine StatPearls
WBC above 15,000 cells/μL · albumin below 3 g/dL · creatinine above 1.5 × premorbid Markers of severe disease.
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Abdominal imaging / lower endoscopy
Colonic dilation above 6 cm in toxic megacolon Used especially in fulminant colitis or when other diagnoses are considered.
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Test of cure CDC
Not recommended CDC: repeat testing "is not recommended if the patient’s symptoms have resolved, as patients often remain colonized." A positive test at the end of therapy does not predict recurrence.
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Pancreatic Cancer Pancreatic ductal adenocarcinoma (PDAC)
Screening in average-risk adults USPSTF 2019 (Grade D)
Not recommended — by any method Grade D: "The USPSTF recommends against screening for pancreatic cancer in asymptomatic adults." Asymptomatic people with new-onset diabetes, smoking, obesity or chronic pancreatitis "are included in this recommendation." It "does not apply" to people with inherited syndromes or familial pancreatic cancer.
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Multidetector (multiphase) CT abdomen
Mass; extent of disease, vessel involvement and metastases "multidetector computed tomography (MDCT) is the best imaging modality to diagnose and evaluate the extent of disease." "Ultrasound is of limited value in pancreatic imaging." MRI and endoscopic ultrasound are also used.
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Endoscopic ultrasound ± biopsy; ERCP with biliary stent
Tissue diagnosis; relief of jaundice EUS can biopsy the mass; "the placement of a biliary stent can help relieve symptoms of jaundice." A biopsy is not always needed before resection when the workup is complete.
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Liver tests, bilirubin, amylase and lipase
Elevated liver tests and direct/total bilirubin (obstruction) StatPearls lab picture; CA 19-9 and CEA are often elevated.
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CA 19-9 (tumor marker) NCI PDQ
Often high at diagnosis; rising level during or after treatment suggests progression Not a screening test. "No tumor-specific markers exist for pancreatic cancer. Markers such as serum cancer antigen (CA) 19-9 have low specificity," and "the presence of a normal CA 19-9 level does not preclude recurrence." High initial CA 19-9 and CEA "can indicate a poorer prognosis."
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Resectability assessment (staging, staging laparoscopy)
Resectable · borderline resectable · unresectable "To appropriately treat pancreatic cancer, it is crucial to evaluate whether the cancer can be resected." Before a Whipple, "a staging laparoscopy is conducted to exclude metastatic disease and ensure resectability."
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[WHIP] Drain fluid amylase
More than 3 times the upper limit of normal serum amylase = possible pancreatic leak Checked on post-operative days 1 and 3; a fistula is defined by this level "usually after postoperative day 3."
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Hepatic Encephalopathy HE
Clinical diagnosis of exclusion
Mental-status change in a patient with liver disease after other causes are ruled out "Hepatic encephalopathy is a diagnosis of exclusion, and neuroimaging should be performed in cases where alternative diagnoses are suspected." Differential: hypoglycemia, hypoxia, alcohol withdrawal, subdural hematoma, intracranial hemorrhage, stroke, meningitis, Wernicke encephalopathy and post-seizure states (StatPearls). "Diagnosing hepatic encephalopathy begins with a comprehensive assessment of the patient’s vital signs and airway."
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West Haven grade StatPearls, citing AASLD/EASL 2014
Grade 1: "Trivial lack of awareness" · 2: "Lethargy or apathy", "Minimal disorientation to time or place" · 3: "Somnolence to semi-stupor, but responsive to verbal stimuli" · 4: "Coma" "Covert hepatic encephalopathy includes minimal hepatic encephalopathy and West Haven grade 1, whereas overt hepatic encephalopathy encompasses grades 2 through 4 of the West Haven criteria."
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Asterixis check
Brief flapping or flexion of the wrist Ask the patient "to fully extend the arms in front of the body, dorsiflex the wrists, and fully extend the digits with the eyes closed." Asterixis is not specific: other toxic-metabolic states (renal or respiratory failure) and drugs such as lorazepam can cause it. "A tremor is a fine rhythmic movement, while asterixis is a coarse, non-rhythmic flapping of the hands."
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Serum ammonia
Often high — but not diagnostic and not a treatment target on its own "Neither elevated arterial nor venous ammonia concentrations are definitive for diagnosing hepatic encephalopathy." "However, a normal ammonia level has a high negative predictive value." Following "the patient’s clinical improvement or deterioration during treatment is more valuable than relying solely on serial ammonia measurements" (StatPearls); KASL notes repeated measurements "can help to determine a treatment’s effects." A high level without symptoms "alone does not justify ammonia-lowering therapy." Sample handling: test "within 1 hour of collection" and keep it cool.
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Glucose, electrolytes, kidney function, ABG
Look for hypoglycemia, low sodium or potassium, kidney injury "Blood glucose levels should also be assessed, as hypoglycemia may occur"; ABG "particularly in higher grades"; hyponatremia and hypokalemia "are known triggers"; kidney injury "is a common precipitant."
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Trigger work-up KASL 2020
Infection screen (CBC, CRP, blood and urine cultures, chest X-ray, diagnostic paracentesis); GI-bleed check (CBC, stool blood, endoscopy) Per the KASL work-up table; "When sepsis is suspected as a trigger, investigations for infection, such as blood cultures, procalcitonin, and C-reactive protein, are essential."
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Number Connection Test (bedside, covert HE)
Slower than expected for age "Patients without hepatic encephalopathy typically complete the test in a duration equal to or less than their age in years."
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CT or MRI; EEG
Rule out other causes Imaging excludes "intracranial lesions, masses, or hemorrhage"; "An EEG can be helpful during the initial evaluation to rule out seizure activity." Neither is specific for HE.
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Esophageal & Gastric Cancer Esophageal cancer
Upper endoscopy with biopsy
Visualizes and samples the tumor; can resect early lesions "Endoscopy is the diagnostic test of choice, allowing for visual inspection, tissue sampling, and resection of early tumors." Suspicious gastric ulcers are biopsied multiple times — sensitivity rises "from approximately 70% with a single biopsy to 98% with 7 biopsies."
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Endoscopic ultrasound (EUS) StatPearls, citing NCCN
Depth of invasion (T stage) and nearby lymph nodes "EUS is instrumental in determining the T stage of the tumor and evaluating the perigastric lymph nodes."
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HER2 testing (gastric)
HER2-positive → eligible for trastuzumab with chemotherapy "Patients eligible for chemotherapy should be tested for HER2 overexpression."
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Barrett esophagus surveillance
Endoscopy and biopsy for dysplasia "Patients with Barrett esophagus are typically monitored through upper endoscopy and biopsy to check for dysplasia." Dysplastic Barrett may be treated with radiofrequency ablation (NCI); superficial lesions may be removed endoscopically.
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CBC
Iron deficiency anemia From chronic blood loss from the tumor (StatPearls).
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[ESOPH-SURG] Water-soluble contrast study
No leak before oral intake "All patients should have a contrast study anywhere from 3 to 7 days postoperatively to rule out any type of leak. If the study is normal, then oral intake can commence." Any sign of a leak also triggers the study.
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[GASTRECT] Vitamin B12 status
Absorption is reduced after all or part of the stomach is removed (NIH ODS) Symptoms of deficiency — fatigue, neurological changes, megaloblastic anemia, glossitis — "can take several years to appear" (NIH ODS).
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Stage and survival (SEER, 5-year relative) NCI SEER (2016–2022)
Esophagus 22.2% overall (localized 48.6% · regional 29.1% · distant 5.3%); stomach 39.8% overall (localized 78.1% · regional 39.0% · distant 8.1%) Esophageal and stomach cancers are most frequently diagnosed at ages 65–74. StatPearls surgical series report different, stage-by-stage figures — do not merge them.
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Renal / Genitourinary

Acute Kidney Injury AKI
Serum creatinine KDIGO 2012 (2026 update in draft)
AKI = rise of ≥ 0.3 mg/dL within 48 hours or ≥ 1.5 × baseline within 7 days. Staging: 1.5–1.9 × = Stage 1 · 2.0–2.9 × = Stage 2 · ≥ 3 × or ≥ 4.0 mg/dL or dialysis started = Stage 3 Creatinine lags behind the injury — in early ATN a normal value does not exclude damage. Reference intervals are age- and sex-dependent, so trend against the patient’s own baseline
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Urine output KDIGO 2012 (2026 update in draft)
< 0.5 mL/kg/h for ≥ 6 hours meets the AKI criterion; < 0.5 for ≥ 12 h = Stage 2; < 0.3 mL/kg/h for ≥ 24 h or anuria ≥ 12 h = Stage 3 The nurse’s number: hourly output against the patient’s weight catches AKI before any lab is drawn
Normal ≥ 0.5 mL/kg/h
BUN : creatinine ratio
> 20:1 favors pre-renal (the hypoperfused kidney avidly reabsorbs urea); ATN runs ≈ 15:1, intrinsic disease closer to 10:1 Upper GI bleeding can push the ratio very high without any kidney problem — check the whole picture
Normal ≈ 10:1
FENa (fractional excretion of sodium)
< 1% = pre-renal (working tubules hoarding sodium) · > 2% = intrinsic/ATN (damaged tubules leaking it) Diuretics confound the result. Fractional excretion of urea (< 35% pre-renal, > 50% intrinsic) is the fallback. Supporting pattern: pre-renal urine sodium < 20 mEq/L with concentrated urine (osmolality > 500 mOsm/kg)
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Urinalysis with sediment
Muddy brown granular casts = ATN; WBC casts and sterile pyuria point to acute interstitial nephritis The sediment is the closest thing to a biopsy the bedside gets — a clean sediment with a high BUN:Cr ratio says pre-renal
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Bladder scan + renal ultrasound
Bladder scan easily identifies urinary retention; ultrasound shows hydronephrosis in post-renal obstruction Noninvasive, radiation-free, and fast — do the bladder scan early in any falling-output workup before assuming a pre-renal or intrinsic cause
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Chronic Kidney Disease & Dialysis CKD
eGFR (with serum creatinine) KDIGO 2024
< 60 mL/min/1.73 m² for ≥ 3 months defines CKD · < 15 (G5) = kidney failure · G3a 45–59 · G3b 30–44 · G4 15–29 CKD-EPI is the preferred equation. Stage G5 also includes anyone on dialysis regardless of the number
Normal ≥ 90 mL/min/1.73 m²
Urine albumin-to-creatinine ratio (uACR) KDIGO 2024
≥ 30 mg/g marks kidney damage — A2 30–299 · A3 ≥ 300; this is what makes G1/G2 count as CKD despite a preserved GFR Collect on an early-morning spot sample; eGFR + uACR together stage every patient
Normal A1 < 30 mg/g
Serum potassium StatPearls
Rises as excretion fails — a medical emergency above 6.5 mEq/L; refractory K⁺ > 6.5 is an urgent dialysis indication ACE inhibitors and nonselective beta-blockers push it higher; so do salt substitutes
Normal —
Hemoglobin + iron studies FDA ESA label · KDIGO 2026
Anemia becomes common as GFR falls (more than half of people in G4–G5); treat with an ESA when Hgb < 10 g/dL — but give iron first if ferritin < 100 μg/L or transferrin saturation < 20% (on hemodialysis, KDIGO 2026 suggests starting iron if ferritin ≤ 500 ng/mL and TSAT ≤ 30%) Check iron stores before and during ESA therapy — an ESA without iron builds nothing
Normal —
Phosphate · calcium · PTH (CKD-MBD panel) KDIGO 2017 CKD-MBD
Dialysis goals: lower elevated phosphate toward the normal range · avoid hypercalcemia · keep PTH ≈ 2–9× the assay’s upper limit Do not suppress PTH below 2× — that trades hyperparathyroid bone for adynamic bone disease. Chronicity clue: a normal PTH suggests AKI rather than CKD
Normal —
UTI & Pyelonephritis UTI
Urinalysis — nitrites StatPearls
Positive when nitrate-reducing bacteria (E. coli, Proteus, Enterobacter, Klebsiella) convert urinary nitrate to nitrite. Specificity 92–100% but sensitivity only 19–48% A positive nitrite strongly suggests UTI; a negative does not rule it out — in pyelonephritis, nitrites are positive in only ~25% of patients
Normal Negative
Urinalysis — leukocyte esterase & WBCs (pyuria) StatPearls
Leukocyte esterase positive (WBC enzyme marking urinary-tract inflammation); > 10 WBC/HPF is abnormal — pyuria is the most common finding in acute pyelonephritis In a patient with UTI symptoms, a negative dipstick does not rule out infection — send the culture when indicated. False-negative esterase with high specific gravity, glycosuria, ketonuria, proteinuria, some oxidizing drugs
Normal 0–5 WBC/HPF; leukocyte esterase negative
Urine microscopy — WBC casts
WBC casts point to renal-level inflammation — pyelonephritis (also interstitial nephritis, glomerulonephritis) A cast is a mold of the renal tubule — it can only have formed in the kidney, so it localizes the infection to the upper tract
Normal No casts
Urine culture StatPearls
Classic cutoff ≥ 100,000 CFU/mL; in symptomatic patients much lower colony counts can still mean infection. In a catheterized patient, infection is defined by a catheter in place ≥ 2 days, at least one symptom or sign, and ≥ 1,000 CFU/mL of a single species Not indicated for uncomplicated outpatient cystitis; strongly recommended — before antibiotics — for pyelonephritis, complicated UTI, pregnancy, treatment failure, recurrence, and hospitalized patients
Normal Bacteria normally absent
Clean-catch midstream specimen
Midstream voided clean-catch specimens are the most accurate; squamous epithelial cells in the sample mean genital-skin contamination (normal ≤ 15–20/HPF) Wash hands, void a small amount into the toilet first, then collect midstream. Examine the UA ideally within 1 hour (refrigerate at 4 °C up to 24 h)
Normal —
CT abdomen/pelvis with IV contrast StatPearls
The imaging study of choice for pyelonephritis when imaging is indicated: diabetes, recurrent pyelonephritis, anatomic abnormality, sepsis, urolithiasis, transplant, immunosuppression, solitary kidney, worsening renal function, or fever > 48 hours despite treatment Blood cultures are frequently drawn in pyelonephritis but rarely change treatment — the urine culture is the one that steers therapy
Normal —
Kidney Stones
Non-contrast CT of the abdomen and pelvis
The gold standard — "the most sensitive and reliable test to diagnose urolithiasis"; identifies stone location and size plus hydroureter, hydronephrosis and ureteral edema It also supplies the two numbers that decide treatment: skin-to-stone distance and stone density in Hounsfield units. Pure uric acid stones read about 500 HU, calcium stones about 900 HU, and struvite 900 HU or less — which is how a radiolucent stone is characterized without an X-ray
Normal —
Ultrasound
The preferred first-line study in pregnancy, with no ionizing radiation; shows hydronephrosis and the resistive index Resistive index = (peak systolic velocity − end diastolic velocity)/peak systolic velocity; a value of 0.75 or above suggests obstruction. If ultrasound is nondiagnostic in pregnancy, options include "conservative measures and observation, low-dose CT imaging, magnetic resonance urography, or ureteroscopic surgery."
Normal Resistive index 0.7 or less is normal
Plain film (KUB)
Screens for radiopaque stones only It may miss stones smaller than 5 mm and misses radiolucent types entirely. Uric acid stones are invisible on plain film because they lack calcium, so a uric-acid stone former is followed with ultrasound or CT — never with a KUB alone
Normal —
Urinalysis
Hematuria in about 85%; assess also for crystalluria, pH and signs of infection (nitrites, leukocytes) Crystal morphology names the stone: uric acid crystals are rhomboid or rosette and yellow or reddish-brown in acidic urine; struvite crystals have a "coffin-lid" morphology in alkaline urine above pH 7.2. The infection threshold that justifies antibiotics is at least 10 WBCs per high-power field (or more WBCs than RBCs), bacteriuria, or positive nitrites
Normal —
Stone analysis
Composition of any passed or removed fragment — the result that determines every prevention decision that follows "Any person who forms or passes a renal stone should undergo imaging and laboratory analysis of the stone," and "all stone material should be collected and sent for chemical analysis." Without it, prevention is guesswork: the diet, the urine-pH target and the drug all differ by stone type
Normal —
24-hour urine testing StatPearls (24-hour urine testing)
Identifies a metabolic abnormality in over 93% of stone formers. Optimal targets: volume 2,500 mL/24 h, specific gravity consistently 1.005 or less, calcium < 200 mg, oxalate < 25 mg/day, citrate about 640 mg or more, urine uric acid < 600 mg/24 h, sodium < 150 mg/24 h Never collected during the acute episode — obtain it once the stone event has been treated. Recommended for all pediatric stone formers, adults with significant renal failure or high surgical risk, and those with multiple stones, repeated stone surgery, a renal transplant, a solitary kidney or chronic diarrhea. Repeat after several months of therapy, then annually
Normal Collection adequacy is confirmed by creatinine 20–25 mg/kg in men and 15–20 mg/kg in women per 24 hours
Acute laboratory panel European guideline panel, as reported by StatPearls
Urine hematuria, pH and bacteria; urine culture; BUN, creatinine, calcium, uric acid; CBC, CRP and coagulation profile Rising creatinine with obstruction is an indication for urgent intervention. Interpret the white count alongside fever, pyuria and hemodynamics — it supports the picture rather than making the diagnosis
Normal —
Glomerulonephritis GN
Urinalysis with microscopy
More than 5 RBCs/HPF with acanthocytes, dysmorphic RBCs and red blood cell casts, occasionally white cell casts "Dysmorphic RBCs… acanthocytes, and RBC casts are pathognomonic of glomerulonephritis." The cast is a mould of the tubule, formed when distorted red cells are encased in Tamm-Horsfall protein — so the bleeding must have started above the tubule, at the glomerulus, which rules out a bladder, prostatic or stone source in a single step
Normal Upper limit of normal is 3 RBCs/HPF
Complement C3 and C4
Low in immune-complex disease — post-streptococcal glomerulonephritis, infective endocarditis and SLE. In PSGN, C3 is low in the acute phase and returns to normal within 6 to 8 weeks, with C1q and C4 typically not consumed The low C3 with normal C4 pattern is the alternative-pathway signature and the fastest way to narrow the differential. Its corollary is a red flag: normal complement in a suspected PSGN is one of the three reasons to biopsy, because it means the diagnosis is something else
Normal —
Streptococcal serology — ASO and anti-DNase B
High titres "indicate a recent streptococcal infection"; anti-hyaluronidase is also used Match the marker to the route. "Elevated anti-streptolysin O titers are commonly observed after pharyngitis" — so ASO is the throat marker, and anti-DNase B is the one that matters after impetigo. No rise in antistreptococcal antibodies is the second of the three reasons to biopsy a suspected PSGN
Normal —
Autoimmune serology panel
ANA and anti-dsDNA (highly sensitive for SLE); ANCA — C-ANCA is 90% PR-3 reactive, P-ANCA 90% MPO reactive; anti-GBM antibodies; hepatitis B and C serology; serum protein electrophoresis Two caveats prevent false reassurance. About 10% of patients with biopsy-confirmed anti-GBM disease have no detectable circulating antibody, so a negative test does not exclude it. And 10% to 50% of anti-GBM patients also carry ANCA, usually anti-MPO — dual positivity is itself an indication to add plasma exchange (KDIGO 2024 Practice Point 9.3.1.10)
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Renal function and proteinuria quantification KDIGO 2025 IgA nephropathy guideline
Plasma creatinine and urea, with creatinine used to estimate GFR and stage the disease; proteinuria quantified by protein-to-creatinine ratio or 24-hour urinary protein The proteinuria number carries prognostic weight in IgA nephropathy: sustained proteinuria of 1 g/day or more confers a 46-fold increased risk of end-stage renal disease compared with under 500 mg/day. It is also the only validated early biomarker for guiding treatment decisions — so it appears as two different numbers that must not be confused. Treatment target: keep proteinuria below 0.5 g/day, ideally below 0.3 g/day (KDIGO 2025 IgA nephropathy guideline), accepting that extensive scarring may make that unreachable. Threshold to consider IgA-targeted treatment (Nefecon, or a reduced-dose glucocorticoid where Nefecon is unavailable): proteinuria of 0.5 g/day or more, on or off treatment (KDIGO 2025). The overall aim is to slow loss of kidney function to the physiological rate, under about 1 mL/min per year in most adults
Normal —
Renal biopsy with immunofluorescence
The pattern is the diagnosis: mesangial granular IgA = IgA nephropathy; bright linear IgG and C3 along the GBM = anti-GBM disease; crescents = rapidly progressive glomerulonephritis Biopsy "will provide the definite underlying cause," and in RPGN "histological diagnosis through renal biopsy is the mainstay." PSGN is the exception — generally no biopsy is needed "unless atypical features are present, such as rapidly progressive glomerulonephritis, normal complement levels, or no rise in antistreptococcal antibodies." Note also that serum IgA level is not a diagnostic test — it lacks "sensitivity and specificity for IgAN diagnosis". In IgA nephropathy the biopsy is scored by the revised Oxford MEST-C classification — mesangial hypercellularity, endocapillary hypercellularity, segmental sclerosis, tubular atrophy/interstitial fibrosis, and crescents. Crescents are a formal component of that score, but KDIGO finds "insufficient evidence to base treatment decisions solely on the presence and number of cellular/fibrocellular crescents," and crescents without a concomitant change in serum creatinine "do not constitute rapidly progressive IgAN" — the rate of change in eGFR is what the histology must be read against
Normal —
Serum potassium with ECG
Hyperkalemia is a listed complication; the threshold is above 5.0–5.5 mEq/L, and symptoms appear above 6.0 mEq/L ECG progression: peaked T waves at 5.5–6.5 mEq/L, flattening or loss of P waves at 6.5–7.5, QRS widening at 7–8, and severe arrhythmias with a sine-wave pattern at 8–10. The heralding cue in this disorder is simple — falling urine output with a rising potassium
Normal —
Chest imaging in suspected pulmonary-renal syndrome
"Patchy parenchymal opacifications, which are usually bilateral and bibasilar" "The apices and costophrenic angles are generally spared" — a distribution detail that helps separate alveolar hemorrhage from pneumonia or pulmonary edema in a patient who is already in renal failure
Normal —
Nephrotic Syndrome
Urine dipstick (protein)
3+ to 4+ proteinuria; a 3+ reading represents 300 mg/dL and correlates with a daily loss of 3 g or more A dipstick measures a concentration, not a rate — a dilute sample understates and a concentrated one overstates. Always confirm with a ratio or a timed collection
Normal Negative or trace
Urine protein-to-creatinine ratio (spot)
Nephrotic range = 2 g of protein per gram of urinary creatinine; reported in children as > 200 mg/mmol and in adults as > 300–350 mg/mmol The practical substitute for a 24-hour collection, which children rarely complete accurately — no timing, no missed voids, no refrigerated jug
Normal —
24-hour urine protein StatPearls
3 g or more per 24 hours is diagnostic; adult figures are quoted as 3 to 3.5 g per 24 hours The reference standard for quantifying the leak. The urine albumin-to-creatinine ratio estimates the same 24-hour albumin loss with a single specimen
Normal —
Serum albumin
Low — diagnostic cutoff below 30 g/L (3.0 g/dL); frequently below 2.5 g/dL in active minimal change disease Also the thrombosis risk dial: at or below 2.8 g/dL VTE risk is significantly higher, and each further 1 g/dL drop roughly doubles it. Below 1.5 g/dL loop diuretics stop working
Normal 3.5–4.5 g/dL
Urine microscopy
Hyaline, granular, fatty, waxy, and epithelial-cell casts with lipiduria — oval fat bodies and fatty casts The discriminator: dysmorphic RBCs and RBC casts argue against nephrotic syndrome and point to a nephritic process instead. Red cell casts are generally absent here
Normal —
Lipid panel
Raised total cholesterol and LDL, raised IDL/VLDL and triglycerides, raised lipoprotein(a), and a fallen HDL-to-total-cholesterol ratio The abnormality tracks disease activity — cholesterol and PCSK9 levels return to normal on remission, so the panel is a response marker as well as a risk marker
Normal —
Metabolic panel
Low total protein, low albumin, and low total calcium; creatinine varies with the degree of renal impairment The calcium falls largely because so much circulating calcium is albumin-bound
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Kidney biopsy KDIGO 2025 pediatric nephrotic syndrome guideline (≥ 12 y); StatPearls (< 1 y)
Establishes the underlying lesion — in FSGS, segmental solidification of the glomeruli with foot-process effacement on electron microscopy and IgM/C3 in sclerotic areas In a child aged 1 to 12, normotensive, with normal renal function and at most microscopic hematuria, a steroid trial is given without a biopsy — "a kidney biopsy is not usually needed at initial presentation and is instead reserved for children with resistance to therapy or an atypical clinical course." Biopsy indications: onset before 1 year or at 12 years or older, gross hematuria, low C3, marked hypertension, raised creatinine, positive secondary-cause serology, steroid resistance, or frequent relapses
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BPH & Urinary Retention BPH
International Prostate Symptom Score (IPSS)
Seven questions scored 0–5 each. Mild 0–9 · moderate 10–19 · severe 20–35 Covers incomplete emptying, frequency within 2 hours, intermittency, urgency, weak stream, straining, and nocturia. Action threshold: a score of 10 or more suggests that BPH treatment should be initiated, increased, or otherwise modified
Normal —
Post-void residual (PVR)
Under 100 mL normal · up to 200 mL acceptable · over 200 mL inadequate emptying · over 300 mL suggestive of retention · over 400 mL is considered urinary retention Timing is part of the measurement: scan immediately after voiding — "delays of as little as 10 minutes… caus[e] clinically significant overestimation." A late scan reads falsely high and can manufacture a diagnosis
Normal Less than 100 mL
Bladder ultrasound scan
Non-invasive volume estimate using the prolate-ellipsoid formula (length × width × height × 0.52); averages about 45 seconds versus 293 seconds for catheterization Catheterization is more accurate but invasive, risking urethral trauma, UTI and discomfort. Scan accuracy is degraded by severe abdominal scarring, ascites, obesity, pregnancy, pelvic masses, bowel obstruction, fibroids or severe prolapse
Normal —
Uroflowmetry (peak flow, Qmax)
Peak flow under 10 cc/sec indicates possible obstruction; the classic BPH urodynamic pattern is a low peak flow under 10 cc/sec with a normal or high detrusor voiding pressure "A voided volume ≥150 mL is sufficient for valid measurement" — a patient who voids a small sample produces an uninterpretable result, so coach fluid intake before the test
Normal Peak flow of 13 cc/sec or more is acceptable
Serum creatinine / basic metabolic panel
May be the only abnormality in silent chronic retention — an unexplained rise in a man with LUTS is post-renal until proven otherwise Checked alongside sodium, potassium, bicarbonate, chloride, BUN and a CBC. This is the test that catches the painless form before the kidney damage becomes irreversible
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Renal ultrasound
Looks for hydronephrosis; bilateral hydronephrosis "is highly suggestive of chronic urinary retention" Indicated for high residual volumes, acute or chronic retention, or unexplained renal impairment; one chapter sets the trigger at a PVR over 1500 mL, new renal failure, or azotemia
Normal —
Prostate-specific antigen (PSA)
Raised in proportion to gland volume — "benign prostates of 35 cc size will typically generate a PSA of 1.5 ng/mL" BPH raises PSA but is not a risk factor for prostate cancer. Check PSA before starting a 5-alpha-reductase inhibitor or operating, because that class reduces serum PSA by 50% — a "normal" PSA on finasteride may be masking a doubled true value
Normal —
Cystoscopy
Estimates prostate size and shape, evaluates the degree of obstruction, and visualizes signs of bladder damage It is strongly recommended before BPH surgical intervention. Pressure-flow urodynamics are not routine, reserved for uncertain diagnoses or when the benefit of surgery is unclear
Normal —
Urinary Incontinence UI
Urinalysis
Look for infection, glucose, protein or blood "Urinalysis should be performed on all patients to assess for urinary tract infection, glycosuria, proteinuria, and hematuria."
Normal —
Post-void residual (bladder scan or catheter)
High (> 200 mL) suggests overflow; low in urge incontinence StatPearls (UI): > 200 mL "suggests overflow urinary incontinence and possible bladder hypotonicity." StatPearls (urge): "post-void residual volume of more than 50 mL" is among reasons to consider specialist referral.
Normal —
Voiding (bladder) diary
Fluid intake, voids, leaks, activities, medication timing StatPearls: "A 24-hour or 3-day voiding diary may be helpful in selected cases." Open RN includes "Medication use, such as diuretics, and the timing of administration."
Normal —
Cough stress test
Leak with cough = stress incontinence "The test is more sensitive when performed in a standing position."
Normal —
Urodynamic testing
Only for complicated cases "Urodynamic testing is unnecessary except for complicated (intractable) cases or if surgery is being considered."
Normal —
Bladder & Kidney Cancer Urothelial carcinoma
[BLAD] Urinalysis
Blood — sometimes only microscopic NCI: patients are asked "to give a urine sample as a first step." Hematuria also has other causes — urinary tract infections, kidney or bladder stones, or other kidney problems "could be the cause, not cancer."
Normal —
[BLAD] Cystoscopy, cytology, imaging, transurethral resection with biopsy
Tumor seen, sampled and staged by depth StatPearls: "Modalities used in diagnosing bladder cancer include imaging (eg, ultrasound, computed tomography, and magnetic resonance imaging), cystoscopy, cytology, transurethral resection, and biopsy." "A CT urogram is the gold-standard imaging modality for the upper urinary tract." Urine cytology sensitivity is "only 44% with a high specificity of 96%," so a negative cytology does not rule cancer out.
Normal —
[RCC] CT abdomen and pelvis; chest imaging
Renal mass; staging for lung and other metastases "Imaging remains the mainstay in RCC for diagnosis, screening, follow-up, and treatment monitoring." NCI: "A biopsy may not be needed if the imaging test results provide enough information to make a diagnosis."
Normal —
[RCC] Urinalysis, renal function, electrolytes, calcium, CBC, liver tests
Look for kidney impairment and paraneoplastic changes Renal function "in order to help make decisions on the use of contrast for radiologic tests"; calcium, blood counts and liver tests screen for hypercalcemia, erythrocytosis and Stauffer syndrome.
Normal —
[CONDUIT] Electrolytes, blood gases, vitamin B12
Watch for hyperchloremic metabolic acidosis and low B12 "Ammonia and chloride from the urine can be absorbed, causing hyperchloraemic metabolic acidosis" — in up to 15%. B12 "Levels should be checked at follow-up appointments every 6-12 months" (StatPearls).
Normal —
Stage and survival (SEER, 5-year relative) NCI SEER (2016–2022)
Bladder 79.1% overall (in situ 98.0% · localized 73.0% · regional 41.8% · distant 9.6%); kidney and renal pelvis 79.2% (localized 93.6% · regional 77.6% · distant 20.3%) About half of bladder cancers are found in situ. Bladder cancer is most often diagnosed at ages 65–74.
Normal —
Polycystic Kidney Disease PKD
Kidney ultrasound (first imaging test) NIDDK / KDIGO 2025
Multiple cysts in both kidneys, interpreted with age and family history NIDDK: "Health care providers diagnose ADPKD using imaging tests and genetic testing. A health care provider can make a diagnosis based on these tests and your age, family history of PKD, and how many cysts you have." KDIGO: "For screening adults at risk of ADPKD, we recommend first using abdominal imaging."
Normal —
MRI — total kidney volume; Mayo Imaging Classification
Kidney and cyst size tracked over time; larger kidneys for age predict faster decline "Total kidney volume is the primary predictive biomarker of future GFR loss" (StatPearls). KDIGO: "We recommend employing the Mayo Imaging Classification (MIC) to predict future" kidney function decline.
Normal —
Genetic testing and counseling
PKD1 or PKD2 variant KDIGO: "Genetic testing can diagnose ADPKD in people with or without a known family history." NIDDK suggests talking "with a genetics counselor as part of your health care team."
Normal —
Home and office blood pressure KDIGO 2025
KDIGO target for ages 18–49 (CKD G1–G2, BP above 130/85 mm Hg): 110/75 mm Hg or lower by home BP monitoring, "if tolerated"; age 50 and older: "a target mean systolic blood pressure (SBP) of <120 mm Hg, if tolerated," by standardized office measurement KDIGO suggests out-of-office measurement with home BP monitoring for people with ADPKD. The older NIDDK page (2017) gives a single goal — "Aim for a blood pressure goal of less than 120/80" — and is superseded by the age-stratified KDIGO 2025 targets.
Normal —
Suspected cyst infection — urine and blood cultures
Fever above 38 °C (100.4 °F), flank pain, raised white count or CRP KDIGO: "A urine culture should be obtained before antibiotics are started for UTI, especially for upper UTI and/or suspected kidney cyst infection. Blood cultures should be obtained if an upper UTI or kidney cyst infection is suspected."
Normal —
Unenhanced CT (stones)
Uric acid and/or calcium oxalate stones "Unenhanced CT scans of the abdomen and pelvis are the most helpful for diagnosing nephrolithiasis in ADPKD patients." "Most stones are composed of uric acid, calcium oxalate, or both."
Normal —
Aneurysm screening — time-of-flight MRA (selected patients) KDIGO 2025
Offered to those with a personal history of subarachnoid hemorrhage or a family history of aneurysm, SAH or unexplained sudden death KDIGO: "We recommend screening for ICA in people with ADPKD and a personal history of SAH or a positive family history of ICA, SAH, or unexplained sudden death in those eligible for treatment and who have a reasonable life expectancy (1D)," using "Time-of-flight magnetic resonance angiography (MRA) without gadolinium enhancement."
Normal —
Tolvaptan liver tests (ALT, AST, bilirubin) JYNARQUE label
Normal before and throughout treatment Boxed warning: "Measure ALT, AST and bilirubin before initiating treatment, at 2 weeks and 4 weeks after initiation, then monthly for the first 18 months and every 3 months thereafter."
Normal —

Hematologic

Anemias
Hemoglobin WHO 2024 (via StatPearls); severity per NCI
Men < 13.0 g/dL · nonpregnant women < 12.0 g/dL · pregnant < 11.0 g/dL (1st/3rd trimester) defines anemia. Severity: mild 10.0–LLN · moderate 8.0–10.0 · severe 6.5–7.9 · life-threatening < 6.5 The Hgb-7 anchor: transfusion is indicated below 7 g/dL or per clinical context (below 8 with acute coronary syndrome)
Normal Reference ranges vary by lab
MCV
< 80 fL microcytic (iron) · 80–100 normocytic (chronic disease/CKD, aplastic) · > 100 fL macrocytic (B12/folate) The first fork of the workup — but ⅓ of B12-deficient patients have no macrocytosis, so a normal MCV never rules B12 out
Normal 80–100 fL
Ferritin + iron studies StatPearls
Iron deficiency: ferritin < 30 ng/mL (92% sensitive/98% specific), low iron, high TIBC, TSAT < 20%. Chronic disease: high ferritin, low TIBC Ferritin < 45 ng/mL without a clear cause → GI evaluation (EGD + colonoscopy) — occult bleeding is easily overlooked
Normal TSAT 25–35%
Reticulocyte count
Production index ≥ 3 = marrow responding (hemolysis, acute blood loss) · < 2 = production failure (deficiency, marrow failure, CKD) Reticulocytosis takes 3–5 days to appear after hemolysis begins — an early normal count doesn’t exclude it
Normal —
B12, MMA & homocysteine
B12 < 200 pg/mL = deficient (200–300 borderline). MMA ↑ + homocysteine ↑ = B12 deficiency; homocysteine ↑ with normal MMA = folate deficiency (serum folate < 2 ng/mL) Hypersegmented neutrophils (≥ 5 lobes) precede macrocytosis; anti-intrinsic-factor antibodies (~100% specific) confirm pernicious anemia
Normal B12 > 300 pg/mL
Hemolysis panel
↑ LDH · ↑ indirect bilirubin · ↑ reticulocytes · ↓ haptoglobin (the most sensitive marker); positive direct Coombs = autoimmune cause Smear tells the mechanism: schistocytes (mechanical), spherocytes (autoimmune/hereditary spherocytosis), bite cells (G6PD)
Normal —
Sickle Cell Disease & Vaso-Occlusive Crisis SCD
Newborn screen → hemoglobin electrophoresis StatPearls
HbS detected at birth (screening is universal in the US); electrophoresis confirms and separates disease from trait (HbAS: about 40% HbS, 60% HbA) All US states screen newborns (implemented nationwide by 2007) using high-performance liquid chromatography or isoelectric focusing — which is why dactylitis at 6 months should never be the first clue
Normal —
Hemoglobin (CBC) StatPearls
Chronically low in HbSS — compensated, and this patient’s "normal" Know the individual baseline: an acute drop of ≥ 2 g/dL with an enlarging spleen means sequestration; a drop of 3–6 g/dL with low retics means aplastic crisis
Normal —
Reticulocyte count
Chronically elevated — the marrow compensating for hemolysis The crisis differentiator: normal/high in splenic sequestration (marrow intact, blood trapped) vs low in aplastic crisis (marrow suppressed)
Normal —
Peripheral smear
Sickle-shaped cells, Howell-Jolly bodies, target cells, polychromasia Howell-Jolly bodies are nuclear remnants a working spleen would have removed — visible proof of functional asplenia
Normal —
Hemolysis labs StatPearls
↑ LDH, ↑ indirect (unconjugated) bilirubin → clinical jaundice Crisis workup adds CBC with differential, CMP, LFTs, and a type and screen — transfusion may be needed fast; cultures and CRP/procalcitonin if febrile
Normal —
Chest X-ray StatPearls
A new pulmonary infiltrate involving at least one lung segment defines acute chest syndrome Clinicians keep a low threshold to obtain chest films during any crisis — early identification of ACS lowers mortality
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Transcranial Doppler (TCD) ASH 2020
Screening study — abnormal = time-averaged mean maximum velocity ≥ 200 cm/s Annual screening for children with HbSS or HbSβ⁰ thalassemia, ages 2–16; an abnormal result starts a regular transfusion program (HbS kept < 30%) for at least a year
Normal —
Disseminated Intravascular Coagulation DIC
Platelet count
Falling — "the commonest laboratory diagnostic feature of DIC" Non-specific on its own, and platelet activation in DIC can create "inaccuracy when using automated platelet counting." The falling trend matters more than any single value
Normal —
Prothrombin time (PT) ISTH 2001 criteria (as reported by Annals of Laboratory Medicine)
Prolonged — and this is the preferred coagulation test, not aPTT The ISTH DIC Subcommittee "recommends PT as the coagulation test of choice," because "aPTT can be shortened owing to increased Factor VIII levels from the acute phase response, aPTT prolongation may lag behind the clinical manifestations." Both are prolonged in established DIC, but aPTT can mislead early
Normal —
Fibrinogen
Falling — but a single normal value does not exclude DIC Absolute low fibrinogen has a "low sensitivity (22%)," because fibrinogen "is also an acute-phase reactant" — it can start elevated and be consumed rapidly while still reading normal. Watch the decreasing level, not the threshold
Normal —
D-dimer / fibrin degradation products
Elevated — "high sensitivity but low specificity" "Different commercial assays have different normal ranges, which are not interchangeable," and "increasing levels may be from renal and/or liver impairment affecting clearance." Compare a patient to their own previous result, not to another lab’s range
Normal —
Peripheral blood smear
Schistocytes — fragmented erythrocytes Red cells shredded as they pass intravascular fibrin strands; they "are characteristic of thrombotic microangiopathic conditions and reflect intravascular hemolysis." Their presence confirms that clotting is happening inside the vessels, not just that numbers are low
Normal —
ISTH overt DIC score (2001 criteria) Score and cutoff: ISTH 2001 criteria (as reported by Annals of Laboratory Medicine and Res Pract Thromb Haemost). 2025 update: ISTH, via Iba et al., Semin Thromb Hemost 2026
Platelets ≥ 100 × 10⁹/L = 0, < 100 = 1, < 50 = 2 · D-dimer/FDP no rise = 0, moderate = 2, strong = 3 · PT prolonged < 3 s = 0, 3 to < 6 s = 1, ≥ 6 s = 2 · fibrinogen ≥ 1 g/L = 0, < 1 g/L = 1. A score of 5 or more is compatible with overt DIC Applied only to a patient with an underlying condition known to cause DIC. Reported sensitivity ≈ 90% and specificity ≈ 97%, with an overall positive predictive value of 68% at a score of 5 or more — but stratified that is 47% at exactly 5, 68% at 6, and 88% at 7 or above, so a borderline score is far weaker evidence than the headline figure implies. The ISTH published an updated definition and diagnostic criteria in 2025; its full point table is not openly published, so this row teaches the 2001 criteria the page’s sources carry. On record from the update: D-dimer above 3× and above 7× the upper normal limit now score 2 and 3 points, with platelets, PT-INR and fibrinogen remaining key indicators
Normal —
Sepsis-induced coagulopathy (SIC) score
Built from platelet count, PT ratio, and the SOFA score; 4 or more points is required The earlier-warning alternative in sepsis — it "was more sensitive than the ISTH criteria to detect coagulopathy," so it can flag the patient before the ISTH score does
Normal —
Antithrombin level
Reduced, with significant reductions correlating with severity and outcome Of limited use for early detection — "their sensitivity for early DIC is unclear as DIC is usually obvious from the global coagulation tests when levels are below 50% of normal." It also matters therapeutically: antithrombin concentrate must not be given with concomitant heparin
Normal —
Thrombocytopenia (ITP & HIT) HIT
Complete blood count with differential and peripheral smear
In ITP: isolated thrombocytopenia with a platelet count "characteristically less than 100,000/μL", normal white-cell count, hemoglobin and red-cell indices, and a smear showing "reduced platelet levels with normal or increased size" Always paired with a reticulocyte count and a smear. Repeat the CBC first if the count is startling and the patient is not bleeding — EDTA clumping causes pseudothrombocytopenia
Normal Platelets 150,000–450,000/µL (ITP uses a diagnostic cutoff of 100,000/μL)
Peripheral smear morphology
The finding that redirects the diagnosis: schistocytes → thrombotic microangiopathy or intravascular hemolysis · hypersegmented neutrophils and macro-ovalocytes → folate, B12 or copper deficiency · teardrop cells and nucleated RBCs → marrow infiltration · immature white cells → leukemia · giant platelets → Alport or Bernard-Soulier syndrome The smear is the cheapest test on the page and the one most likely to change the diagnosis outright — it is how TTP and leukemia are caught in a patient who was labelled "ITP"
Normal —
Tests NOT to order in typical ITP ASH (as reported by StatPearls)
Antiplatelet antibody testing "is not recommended when evaluating ITP as it does not correlate with clinical outcomes." Bone-marrow biopsy "is no longer performed for typical ITP presentations" Marrow biopsy is reserved for findings suggesting malignancy or marrow failure. ITP remains a diagnosis of exclusion made on the CBC, the smear, and targeted secondary testing
Normal —
Targeted secondary testing in ITP
Helicobacter pylori testing in patients "with recurrent epigastric pain suggestive of peptic ulcer"; HIV and hepatitis C screening; ANA Interpret ANA carefully — 17.5% of patients with ITP have a positive antinuclear antibody test, so a positive result is not by itself diagnostic of secondary ITP
Normal —
4Ts score (HIT pretest probability) Cuker et al., Blood 2012 (systematic review and meta-analysis)
Four components scored 0–2: thrombocytopenia magnitude, timing of the fall, thrombosis or sequelae, and other causes. Bands: 0–3 low · 4–5 intermediate · 6–8 high Score 4 or more and all heparin stops immediately, including line flushes. Its real strength is exclusion: negative predictive value of a low score is 0.998, while positive predictive value is only 0.64 at a high score and 0.14 at intermediate. Remember the inverted fourth criterion — "none apparent" scores 2
Normal —
PF4 ELISA (heparin-PF4 immunoassay)
Positive when "the optical density (OD) is greater than 0.4" — and the magnitude matters: "less than 3% of patients with an OD of 0.4-1 will have a true positive result", while an OD greater than 2 "correlates with ~ 90% chance of having HIT" "Highly sensitive and has a high negative predictive value" — HIT can be ruled out if this test is negative — but low specificity produces false positives. A positive ELISA needs confirmation
Normal —
Serotonin release assay (SRA) ASH 2018 (as reported by StatPearls)
"Gold standard test for confirming HIT with high sensitivity and specificity" — a positive SRA confirms the diagnosis, and a "negative SRA rules out HIT, even in the setting of a positive ELISA" A functional assay: donor platelets exposed to heparin plus the patient’s IgG release serotonin. The guideline "recommends getting a confirmatory SRA for any patient with a positive ELISA"
Normal —
Platelet count monitoring on heparin ACCP 2012 (as reported by CADTH)
Monitored "every 2 or 3 days from day 4 to day 14 (or until heparin is stopped) for patients receiving heparin who are considered to have more than a 1% risk of HIT" Reported through a review that found no current evidence-based guidelines meeting its criteria, so treat this as a monitoring convention rather than current guidance. The principle it encodes still holds: the HIT window is days 5 to 14, so that is when counts are watched
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Leukemias
CBC with differential
Cytopenias — "decreased leukocytes, hemoglobin, or platelets" — with circulating blasts; or, in the chronic leukemias, marked leukocytosis. CLL requires "an absolute lymphocyte count greater than 5000/mcL" of clonal B cells The differential is what makes the count usable: it establishes the blast percentage and supplies the neutrophil and band percentages needed for the ANC
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Absolute neutrophil count (ANC)
Calculated, not reported: ANC = WBC (cells/microL) × percent (PMNs + bands) / 100. Ladder: mild 1.0–1.5 · moderate 0.5–1.0 · severe below 0.5 · agranulocytosis below 0.2 × 10⁹/L "Once the neutrophil count is below 1.5 × 10⁹/L, recurrent infections become more common" — that is the general neutropenia threshold. The febrile-neutropenia definition uses a different number: below 500 cells/µL, or expected to fall to 500 or below within 48 hours (NCCN definition). Circulating neutrophils are only 3–5% of the body total, so marrow reserve can mitigate a low peripheral count
Normal Above 1.5 × 10⁹/L
Blast percentage (peripheral blood or marrow) European LeukemiaNet 2022 (as reported by StatPearls)
20% or more blasts defines acute leukemia; below 20% is chronic. Normal marrow blasts are 1% to 5% The 2022 European LeukemiaNet guidelines, as reported by StatPearls, modified the AML threshold to 10% or more blasts when recurrent genetic abnormalities are present. In CML, blast phase is 20% or more blasts; the WHO 2022 classification no longer requires a separate accelerated phase (older schemes defined it at 10–19% blasts)
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Peripheral blood smear
Blasts with "high nuclear-to-cytoplasmic ratio, irregular nuclear contour"; Auer rods — "red-staining, needle-like bodies seen in the cytoplasm of myeloblasts" — in AML; smudge cells in CLL, cells that "are disrupted during the process of being spread on a glass slide" In APL the promyelocytes carry "abundant cytoplasmic Auer rods, which resemble clumps of azurophilic granules elongated like needles" — a morphologic cue that should prompt treatment on suspicion rather than waiting for genetics
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Bone marrow aspirate and biopsy
The definitive test — blast percentage, morphology, and material for immunophenotyping and cytogenetics. In AML, complete remission is defined as "less than 5% blasts by aspirate differential" Response is reassessed post-induction at day 14 or on full count recovery (about 28 days). "All blood products must undergo irradiation to prevent transfusion-related graft versus host disease"
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Flow cytometry and immunophenotyping
Establishes lineage. CLL shows characteristic coexpression of CD5, CD19 and CD23 This is what separates ALL from AML when the blasts look similar down the microscope — morphology suggests, immunophenotype decides
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Cytogenetics, FISH and molecular testing
Defines subtype and drives therapy: FLT3, NPM1 and IDH mutations in AML; the Philadelphia chromosome t(9;22) in CML and as a poor-prognosis subgroup in ALL; the FISH panel in CLL for 17p, 11q, 13q deletions and trisomy 12 CML monitoring runs on quantitative PCR for BCR-ABL1
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Baseline tumour-lysis chemistry and cardiac assessment
Tumour-lysis markers — "elevated LDH, uric acid, potassium, and phosphorus levels" — plus ECG and echocardiography "to anticipate potential cardiotoxic effects (eg, from anthracycline therapies)" Both are anticipatory. The chemistry panel establishes the baseline against which tumour lysis syndrome is recognized; the cardiac studies exist because anthracyclines are cardiotoxic. Tumour lysis management is covered on the oncologic emergencies page
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Lymphomas Hodgkin lymphoma
Excisional lymph node biopsy
Reed-Sternberg cells (CD30+, CD15+) in classical HL; a clonal B- or T-cell population in NHL "Excisional lymph node biopsy is the gold standard for diagnosis. Fine needle aspiration of the lymph node is avoided." In HL, FNA or core biopsy "frequently shows non-specific findings." NCI notes that immunophenotyping sometimes makes FNA or core biopsy sufficient
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Whole-body PET-CT
Stages disease and measures response "Whole-body PET/CT imaging is preferred over CT of the chest, abdomen, and pelvis." In HL, "The best predictor of treatment failure is a PET-CT scan obtained after two cycles of chemotherapy (PET2 scan)"
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Lactate dehydrogenase (LDH) and uric acid
Elevated with high tumor burden "LDH levels correlate with the bulk of disease." Bulky disease with high uric acid and LDH means a higher risk of tumor lysis syndrome
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CBC, ESR, chemistry panel, phosphorus, HIV, hepatitis B and C serology NCI PDQ
Cytopenias if the marrow or spleen is involved; baseline organ function NCI’s HL workup. Hepatitis B screening (HBsAg and anti-HBc) is required before rituximab
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Bone marrow biopsy
Marrow involvement changes the stage "PET-CT has replaced bone marrow biopsy in the clinical staging of newly diagnosed HL"; in NHL it is done "when management would change"
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Lugano staging AJCC / Lugano
I — one region · II — two or more regions on the same side of the diaphragm · III — both sides · IV — disseminated extranodal involvement Lugano replaces Ann Arbor. The A/B suffix is used for Hodgkin lymphoma only — "A/B is no longer used in NHL"
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Baseline echocardiogram or MUGA scan
Cardiac function before anthracycline chemotherapy Doxorubicin is cardiotoxic — baseline imaging "should be performed before initiation of chemotherapy"
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Multiple Myeloma MM
Serum and urine protein electrophoresis and immunofixation (SPEP/SIFE, UPEP/UIFE); serum free light chains NCCN, via StatPearls
A monoclonal (M) protein in blood or urine; abnormal free light chain ratio Part of the work-up StatPearls relays from NCCN, with a 24-hour urine protein. An involved/uninvolved free light chain ratio ≥ 100 is one of the SLiM criteria
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Bone marrow aspirate and biopsy
Clonal plasma cells ≥ 10% (≥ 60% is a SLiM criterion); cytogenetics and FISH High-risk FISH findings include t(4;14), t(14;16), t(14;20), del17p and 1q gain. MGUS < 10%; smoldering 10% to 59% without end-organ damage
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Calcium CRAB criteria, via StatPearls
> 11 mg/dL (or > 1 mg/dL above the upper limit of normal) = the "C" in CRAB
Normal —
Creatinine or creatinine clearance CRAB criteria, via StatPearls
Creatinine > 2 mg/dL or clearance < 40 mL/min = the "R" in CRAB "Impaired renal function worsens prognosis regardless of stage"
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Hemoglobin (CBC) CRAB criteria, via StatPearls
Hemoglobin < 10 g/dL (or > 2 g/dL below normal) = the "A" in CRAB; thrombocytopenia and leukopenia possible
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Imaging — whole-body low-dose CT, PET-CT or MRI; skeletal radiographs
Punched-out lytic lesions = the "B" in CRAB; more than one focal lesion > 5 mm on MRI is a SLiM criterion "At diagnosis, whole-body PET scan or MRI of the total spine and pelvis appears to be equally efficacious in the detection of bone lesions"
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Beta-2 microglobulin, albumin, LDH
Prognosis — Revised ISS stage 3 = B2M > 5.5 mg/L with high-risk cytogenetics Stage predicts survival (5-year overall survival 82% in R-ISS I, 62% in II, 40% in III) but "has little influence on the choice of therapy"
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Hemophilia & von Willebrand Disease Hemophilia A (factor VIII deficiency)
aPTT, PT/INR, platelet count
Hemophilia: isolated prolonged aPTT with normal PT/INR and platelets. VWD: often normal screens; aPTT may be prolonged Hemophilia: "a normal aPTT does not exclude mild hemophilia A." VWD: "Screening tests are often normal in VWD, and more specific tests are required."
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Mixing study
Correction = factor deficiency; no correction = inhibitor "failure to correct, either immediately or after incubation, suggests the presence of an inhibitor."
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Factor VIII or IX activity
Severe under 1% · moderate 1% to 5% · mild 5% to 40% "Definitive diagnosis is established by measuring factor VIII activity." "A factor IX activity level below 40% confirms the diagnosis of hemophilia B."
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Inhibitor testing (Bethesda assay)
Antibody against infused factor Nijmegen-modified Bethesda assay; on emicizumab, standard aPTT-based assays are unreliable and "a specialized testing method called the chromogenic Bethesda assay is needed" (CDC)
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VWD panel — VWF antigen, VWF activity (ristocetin cofactor), factor VIII activity, multimers StatPearls (VWD)
VWF activity below 30 IU/dL is diagnostic; 30 to 50 = ‘low VWF’ Tests often need repeating because levels vary "as a result of changes the body might be reacting to―such as stress, pregnancy, and infections"
Normal "Normal Ristocetin cofactor activity levels are above 50 IU/dL."
Genetic testing
F8 (or F9) variant; carrier and prenatal testing "Molecular genetic testing of the F8 gene is now considered standard of care."
Normal —
Polycythemia Vera PV
Hemoglobin / hematocrit (ICC major criterion) ICC (via NCI PDQ)
Hgb > 16.5 g/dL (men) or > 16.0 g/dL (women), or Hct > 49% (men) or > 48% (women), or red cell mass > 25% above predicted Diagnosis needs "either all three major criteria or the first two major criteria with the minor criterion."
Normal StatPearls: men about 16 g/dL ± 2 and 47% ± 6%; menstruating women about 13 g/dL ± 2 and 40% ± 6% — "The reference ranges for normal hemoglobin and hematocrit vary by altitude, ethnicity, and country."
JAK2 V617F or exon 12 variant (major criterion) ICC (via NCI PDQ)
Present "JAK2 mutation studies are diagnostic for polycythemia vera in 95% of cases" (StatPearls, 2026).
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Serum erythropoietin (minor criterion) ICC (via NCI PDQ)
Low — "below reference range" A normal or high EPO points toward secondary polycythemia.
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Bone marrow biopsy (major criterion) ICC (via NCI PDQ)
Hypercellular — panmyelosis (all three lines)
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CBC — white cells and platelets
Often raised alongside red cells Platelets above 1 million/µL → bleeding risk from acquired von Willebrand disease; aspirin is not given.
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Hematocrit during treatment NCI PDQ
Target below 45% "Patients with hematocrits maintained at less than 45% have significantly fewer cardiovascular and thrombotic events compared to when the goal hematocrit is 50%." StatPearls: each 500 mL unit "should drop the hematocrit by 3% in an average-sized adult."
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Transfusion Reactions Blood transfusion reaction
Clerical check at the bedside
Unit label and patient identity match StatPearls: "A clerical check should be performed by examining the product bag and confirming the patient’s identification." Before any transfusion, two qualified professionals verify the product.
Normal —
Return the unit and send a fresh blood sample
Blood bank repeats ABO typing and crossmatch on pre- and post-transfusion samples Send the bag and tubing if possible with a freshly collected sample; the blood bank runs the transfusion reaction evaluation.
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Direct antiglobulin test (DAT, Coombs)
Positive in hemolytic reactions In delayed reactions, a positive DAT between 24 hours and 28 days after transfusion with a new red-cell antibody (CDC Biovigilance criteria, via StatPearls).
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Hemolysis labs — haptoglobin, LDH, bilirubin, plasma and urine free hemoglobin
Low or absent haptoglobin, raised LDH and unconjugated bilirubin, hemoglobinemia, hemoglobinuria Look at serum and urine for pink color.
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Coagulation — PT, aPTT, fibrinogen, D-dimer
Abnormal if DIC develops Checked in suspected acute hemolysis.
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Chest imaging and oxygenation
TRALI: new bilateral infiltrates, SpO2 90% or less on room air or PaO2/FiO2 below 300 mm Hg, no evidence of pulmonary vascular overload TACO instead shows signs of fluid overload with raised BNP and a response to diuretics.
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BNP / NT-proBNP
Raised in TACO Supports volume overload rather than TRALI.
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Baseline and serial vital signs
Temperature, pulse, BP, respirations and SpO2 before, during and after StatPearls (Blood Transfusion): document after 15 minutes, then every hour, and at the end; StatPearls (Transfusion Reactions): typically every 15 minutes. After a reaction, record every 15 minutes. Notify the clinician before starting if the temperature is above 100 °F. Follow agency policy.
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CDC NHSN Hemovigilance case definitions CDC NHSN 2026
National surveillance reporting (AHTR, TACO, TRALI and others) CDC: "surveillance definitions only and are not intended to be used for clinical care" — not bedside diagnostic criteria. Report all transfusion-related deaths to FDA.
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Immune / Infectious

Anaphylaxis & Hypersensitivity Reactions
Clinical criteria (the diagnosis itself) WAO 2020
Anaphylaxis is highly likely with EITHER (1) acute onset (minutes–hours) of skin/mucosal involvement PLUS ≥ 1 of respiratory compromise, reduced BP or end-organ dysfunction, or severe GI symptoms — OR (2) acute hypotension, bronchospasm, or laryngeal involvement after a known/probable allergen, even without skin findings Anaphylaxis is a clinical diagnosis — no laboratory test is required. Treat on recognition; never wait on labs
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Blood pressure WAO 2020
SBP < 90 mm Hg or a > 30% drop from that patient’s baseline defines the hypotension criterion (children < 10 y: SBP < 70 + [2 × age in years]) Know the admission baseline — a "normal-looking" 92/60 is criterion-level hypotension in a patient who runs 140/85
Normal SBP ≥ 90 and within 30% of baseline
Serum tryptase StatPearls
Elevated — supportive evidence of mast-cell degranulation, not required for diagnosis Timing is the nursing job: draw within 15 minutes–3 hours of symptom onset; it may remain elevated up to 6 hours
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Pulse oximetry (SpO₂)
Hypoxemia with respiratory involvement — one of the findings that satisfies the respiratory-compromise criterion High-flow oxygen (preferably 100% via non-rebreather) for any respiratory distress and for anyone needing repeated epinephrine doses (WAO 2020)
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HIV / AIDS HIV
4th-generation HIV antigen/antibody immunoassay CDC, as reported by StatPearls
The standard first test — detects antibodies to HIV-1 and HIV-2 plus the p24 antigen, "enabling earlier identification of infection following exposure" Routine screening is recommended for everyone aged 13 to 64 in healthcare settings, once for most people at low risk and as often as every 3 to 6 months for higher-risk patients; pregnant patients are screened early in pregnancy. Opt-out screening is used — "no U.S. state requires signed consent," but the patient must be verbally informed and given the chance to decline
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Window period & retest timing StatPearls
The eclipse period lasts about 10 days (no test can detect HIV); the window phase runs up to 20–25 days. HIV RNA becomes detectable about a week after infection (assay-dependent), p24 antigen at 13 to 20 days, IgM near 20 days and IgG near 30 days Most people test positive within 3 weeks on a 4th-generation assay, but "some may not seroconvert for up to 3 months." After an exposure, retest during the 4- to 6-week period with a final test at 12 weeks. If the exposure was within 14 days, an HIV RNA test is the initial diagnostic test — a negative antibody result does not rule out acute HIV
Normal A negative test more than 3 months after the last at-risk exposure is considered conclusive
Confirmatory testing
A second, different, preferably laboratory-based test is required — a confirmed HIV case means a second, different test confirms the first. One positive screen is never a diagnosis Antigen positive with antibody negative → reflex HIV RNA test to confirm or exclude infection. Both positive → a confirmatory test differentiates HIV-1 from HIV-2 antibodies. Acute HIV is diagnosed by a positive nucleic acid amplification test or p24 antigen with a negative or indeterminate antibody result
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Plasma HIV-1 RNA (viral load) NIH and WHO definitions, as reported by StatPearls
The indicator of whether treatment is working — "the most important indicator of initial and sustained response to ART." Therapeutic goal: sustained suppression below 50 copies/mL Recheck 4 to 8 weeks after starting ART; suppression below 200 copies/mL "may take up to 24 weeks of continuous therapy"; once suppressed, monitor every 3 to 4 months. Virologic failure is defined as inability to suppress below 200 copies/mL (NIH) or above 1,000 copies/mL on two consecutive measurements over 3 months after 6 months of therapy (WHO)
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CD4+ T-lymphocyte count CDC staging, as reported by StatPearls
The indicator of how much immune damage exists — CD4+ counts are "the best indicators of immune function, disease progression, and survival, and they determine the need to initiate prophylaxis for opportunistic infections." CDC staging: stage 1 ≥ 500 cells/µL · stage 2 200–499 · stage 3 < 200 Monitored every 3 to 6 months for the first 2 years or if viremia develops; after 2 years, every 12 months if the count is 300–500, and above 500 "monitoring is optional." Track the trend, not a single value — each falling threshold opens a new set of pathogens
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Genotypic drug-resistance testing
Baseline testing of reverse transcriptase and protease genes in treatment-naive patients, adding integrase strand transfer inhibitor genes for anyone previously treated with ART or long-acting cabotegravir PrEP Timing is a nursing-relevant rule: draw the sample while the patient is still taking the ART, or as soon as possible after discontinuation — resistant strains fade from the sample once drug pressure is removed. Baseline work-up also includes CBC, glucose, renal and liver panels, urinalysis, lipids, hepatitis A/B/C serology, and pregnancy testing when appropriate
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Serum cryptococcal antigen
Screened when the CD4+ count is 100 cells/mm³ or less — a positive result is what triggers cryptococcal prophylaxis This is an antigen-triggered decision, not a CD4-alone decision. The same logic applies to toxoplasmosis prophylaxis, which requires a positive toxoplasma antibody in addition to a CD4 below 100
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Pneumocystis pneumonia work-up
Chest x-ray shows diffuse bilateral peri-hilar interstitial infiltrates; CT shows ground-glass attenuation or cystic lesions with high sensitivity; serum LDH is elevated, as is serum beta-D-glucan in the right clinical setting Definitive diagnosis is by PCR, dye staining or fluorescein antibody staining of induced sputum or bronchoalveolar lavage fluid — the imaging and LDH build the case, the respiratory specimen closes it. Do not wait for confirmation to escalate a hypoxemic patient
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Systemic Lupus Erythematosus SLE
Antinuclear antibody (ANA) 2019 EULAR/ACR criteria, as reported by StatPearls
The screening test and the entry criterion — sensitivity greater than 97% of SLE cases, but specificity only about 20% The asymmetry is the whole teaching point: a positive ANA "is not diagnostic, but a negative result makes SLE highly unlikely." Immunofluorescence assay is the gold-standard method; ELISA and multiplex are less sensitive. Rare ANA-negative SLE exists. No ANA, no classification — but a positive ANA alone is not lupus
Normal Entry criterion for classification: at least 1:80 on HEp-2 cells or a positive equivalent test
Anti-double-stranded DNA (anti-dsDNA)
Greater than 95% specificity for SLE, but present in only about 40% to 80% of patients — "a negative anti-dsDNA result does not rule out the diagnosis of SLE" Correlates with disease activity and with the development of lupus nephritis, though it may be elevated in minimally active disease. ELISA carries "a high risk of false-positive results," with the Crithidia luciliae immunofluorescence test used for confirmation. Also seen in drug-induced lupus from anti-TNF agents and interferon-α
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Anti-Smith (anti-Sm) 2019 EULAR/ACR criteria, as reported by StatPearls
Present in only 10% to 55% of patients — but with 99% specificity for SLE; more frequently seen in Black individuals Pair it with anti-dsDNA as the specific antibodies — low sensitivity, very high specificity — against ANA as the sensitive one. In the 2019 EULAR/ACR weighting, anti-dsDNA or anti-Sm carries 6 points, the single heaviest immunologic weight
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Complement C3 and C4 2019 EULAR/ACR criteria, as reported by StatPearls
Low in active disease — complement is consumed binding immune complexes, not deficient "C3 and C4 should be checked in patients with SLE or suspected SLE"; low levels "indicate complement consumption and may correlate with disease activity." The flare signature to recognize: rising anti-dsDNA with falling C3 and C4. In the classification criteria, low C3 or C4 scores 4 points
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Urinalysis with protein quantification
Proteinuria, microscopic hematuria, or red blood cell casts; quantify with a 24-hour urine protein or spot urine protein-to-creatinine ratio This is the test that finds the silent kidney. Also expect hypoalbuminemia and a rising serum creatinine as nephritis advances. Proteinuria is the prognostic number afterwards — a 1-year cutoff of 0.7 to 0.8 g/24 h predicts good long-term renal prognosis
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Renal biopsy
Should "always be performed when lupus nephritis is suspected" — histopathology, immunofluorescence and electron microscopy set the ISN/RPS class, and the class sets the therapy Indicated with proteinuria above roughly 500 mg per 24 hours, persistent renal dysfunction, or active urinary sediment. Class IV (diffuse, about 50% or more of glomeruli) carries the worst prognosis; Classes I and II have excellent outcomes. Lupus nephritis is comanaged with a nephrologist in every case
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CBC, chemistry, inflammatory markers
Cytopenias (leukopenia < 4,000/mm³, lymphopenia < 1,500/mm³, thrombocytopenia < 100,000/mm³); CRP and ESR frequently elevated; polyclonal hypergammaglobulinemia Drawn at every activity assessment alongside creatinine and urinalysis. A falling platelet count or new anemia may be lupus, its treatment, or an infection — which is why they are interpreted against complement and anti-dsDNA rather than alone
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Antiphospholipid antibody panel and other specific antibodies
Lupus anticoagulant, anticardiolipin and anti-β2-glycoprotein I — "associated with thrombotic events and adverse pregnancy-related outcomes." Anti-SSA/Ro and anti-SSB/La carry congenital heart block and neonatal lupus risk All pregnant patients with SLE are tested for antiphospholipid antibodies and for anti-SSA/Ro and anti-SSB/La — the results change obstetric management. Anti-ribosomal P is highly specific but rare (< 5%) and may correlate with neuropsychiatric disease; anti-U1-RNP appears in 20% to 40% and also defines mixed connective tissue disease
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Healthcare-Associated Infections HAI
C. difficile stool testing
A two-step, sequential approach: glutamate dehydrogenase (GDH) or nucleic acid amplification testing for detection, followed by enzyme immunoassay for toxin confirmation Test only symptomatic patients — 3 or more loose stools in 24 hours — and never test for cure. "Testing for C difficile infection is unnecessary in asymptomatic patients… asymptomatic individuals with positive stool toxin tests do not require treatment." A positive test in a patient without diarrhea is colonization
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C. difficile severity markers
Severe disease = WBC > 15,000 cells/μL, serum albumin < 3 g/dL, or serum creatinine > 1.5 times the premorbid level Fulminant disease is a clinical picture rather than a lab value: diarrhea, diffuse abdominal pain, abdominal distension, hypovolemia, toxic megacolon, and perforated bowel with peritonitis. Watch for the distension-with-less-stool pattern
Normal Compare creatinine against the patient’s own premorbid baseline, not a population range
Urine culture in a catheterized patient StatPearls (clinical threshold) · SHEA/IDSA 2022 CAUTI compendium update (surveillance definition)
Two thresholds answer two different questions — keep them in separate lanes. Clinical diagnosis: signs of infection that cannot be attributed to another source plus greater than 1,000 CFU/mL of one or more pathogens (StatPearls). Surveillance reporting: significant bacteriuria at at least 100,000 CFU/mL with no more than 2 organisms, plus at least one clinical finding — fever, suprapubic tenderness, or costovertebral angle pain or tenderness (SHEA/IDSA 2022 CAUTI compendium update) The count alone never makes the diagnosis; the symptoms are the gate. That is why the same 100,000 CFU/mL figure means "report this as a CAUTI" when a clinical finding accompanies it and "leave it alone" when nothing does. Screening for asymptomatic bacteriuria in catheterized patients is explicitly not recommended (with limited population exceptions). The commonest pathogens are E. coli, Klebsiella, Enterococcus, Pseudomonas aeruginosa and Candida
Normal Asymptomatic bacteriuria — 100,000 CFU/mL with no symptoms at all — does not warrant treatment (StatPearls)
Blood cultures for suspected CLABSI
Either a single positive culture for an organism not commonly found on skin, or two or more cultures growing skin-flora organisms — with the infection not attributable to another source and not present on admission The surveillance frame is "recovery of a pathogen from a blood culture in a patient who had a central line at the time of infection or within 48 hours before." Leading pathogens: S. aureus 23%, Candida 13%, coagulase-negative staphylococci 12%, Enterococcus 12%, Streptococcus 12%. Draw cultures before the first antimicrobial dose — that timing is a named nursing stewardship duty
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MRSA nasal PCR screening
Identifies colonization, not active infection — the anterior nares are the primary colonization site Resistance is carried by the mecA gene, encoding transpeptidase PBP2a, "lowering the organism’s affinity to bind to beta-lactam antibiotics." Other colonization sites include oropharynx, skin and gastrointestinal tract, with rectum and throat predominating in the ICU. A positive screen guides precautions and decolonization, not antibiotics
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Post-void residual by bladder scanner SHEA/IDSA 2022 CAUTI compendium update
Used to answer "does this patient actually need a catheter?" before one is placed or after one is removed Named explicitly among the alternatives to indwelling catheterization alongside external male or female collection devices, intermittent catheterization, prompted toileting, urinals, bedside commodes and incontinence garments. Non-invasive assessment is what keeps the most preventable HAI from starting
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Surveillance timing definitions
Healthcare-associated = 48 hours or more after admission · VAP = more than 48 hours after endotracheal intubation · SSI = within 30 days postoperatively, or within 90 days with an implant These clocks are what separate an infection the patient brought in from one the care produced, and they drive both reporting and the clinical question of where to look. An infected joint replacement at week ten is still a surgical site infection
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Transplant Rejection & Immunosuppression Allograft rejection
Serum creatinine and eGFR (kidney graft)
A sudden rise of more than 25% from baseline suggests rejection "Kidney allograft function assessed by serum creatinine (Cr) and estimated glomerular filtration rate (eGFR) requires measurement at or before each visit." A rising creatinine is worked up like acute kidney injury "with added workup for the rejection."
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Allograft biopsy Banff classification (via StatPearls)
T-cell-mediated or antibody-mediated rejection; chronic changes "The standard way to detect rejection is a renal allograft biopsy, which accurately grades the severity of rejection, differentiates between different types and guides the treatment."
Normal —
Tacrolimus whole-blood trough level
Within the transplant team’s target range — targets vary by organ, time since transplant and institution "Whole-blood concentrations should be used, typically drawn within 30 minutes before the next dose." "Early and frequent monitoring of tacrolimus whole blood trough levels is recommended." Targets "usually decrease as posttransplant time increases."
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Monitoring on tacrolimus
Renal and hepatic function, K, Mg, phosphate, glucose, blood pressure "Additional monitoring parameters include renal function, hepatic function, serum electrolytes (Mg, Phos, K), glucose, and blood pressure."
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Donor-specific antibodies; BK and CMV PCR; transplant ultrasound with Doppler
Antibody-mediated rejection, viral infection, obstruction or vascular problems Part of the StatPearls work-up for a rising creatinine. Donor-derived cell-free DNA may be positive early, but "it has not been validated to date."
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HLA typing and crossmatch (before transplant)
A negative crossmatch "A transplant surgery cannot be performed if the serum crossmatch is positive."
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Primary Immunodeficiencies Inborn errors of immunity (IEI)
Newborn screen — T-cell receptor excision circles (TREC)
Absent or markedly reduced in SCID "TRECs are byproducts of T-cell receptor rearrangement in the thymus and are absent or markedly reduced in neonates with T-cell lymphopenia, including all forms of SCID." NIAID: screening plus early treatment raised five-year SCID survival "from 73% before the advent of screening to 87% since."
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CBC with manual differential
Lymphocytopenia → T-cell defect "an absolute lymphocyte count < 2500/μL in infants is abnormal."
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Serum immunoglobulins (IgG, IgA, IgM) and vaccine titers
Low immunoglobulins; poor responses to tetanus, diphtheria and pneumococcal antigens "Failure to mount protective titers after vaccination is a hallmark of antibody deficiency." Infants have a physiologic IgG dip "between approximately 3 and 6 months of age" that "usually resolves spontaneously by 24 months."
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Flow cytometry — lymphocyte subsets
Absent or low T cells (CD3, CD4, CD8), B cells (CD19/CD20) or NK cells
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Serum calcium (DiGeorge)
Low StatPearls lists DiGeorge among the genetic causes of hypoparathyroidism; its general (not infant-specific) hypoparathyroidism management is calcium supplements with calcitriol, then calcium checked every few weeks after starting treatment and every 3 to 6 months once stable, together with phosphorus, kidney function and periodic urine calcium — aiming for a serum calcium in the low-normal range (StatPearls, hypoparathyroidism).
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Trough IgG on replacement
Targets differ by disorder CVID: "above 700 to 800 mg/dL" (StatPearls, CVID); DiGeorge on IVIG: "greater than 500 to 600 mg/dL" (StatPearls, DiGeorge).
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Renal function during IVIG FDA label (IGIV)
Watch for rising BUN/creatinine, falling urine output "Monitor renal function, including blood urea nitrogen (BUN), serum creatinine, and urine output in patients at risk of developing acute renal failure."
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Scleroderma & Sjögren’s Systemic sclerosis (SSc)
[Scleroderma] Autoantibodies — ANA, anti-centromere, anti-Scl-70, anti-RNA polymerase III
ANA positive in over 90% Anti-centromere: limited disease and PAH risk; anti-Scl-70: diffuse skin, interstitial lung disease, cardiac involvement; anti-RNA polymerase III: aggressive diffuse skin and renal crisis. NIAMS: "a blood test alone does not diagnose scleroderma."
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[Scleroderma] Blood pressure — clinic and home
New or rising BP may signal renal crisis "Regular blood pressure monitoring at home can aid in early detection of scleroderma renal crisis" — especially early diffuse disease.
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[Scleroderma] Renal function, urine protein, CBC
Renal crisis: rising creatinine, proteinuria; hemolytic anemia and thrombocytopenia "Renal function and 24-hour urine protein or urine protein:creatinine ratio should be closely monitored."
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[Scleroderma] Lungs — HRCT, pulmonary function tests, echocardiogram
ILD on HRCT; restrictive PFTs; raised pulmonary pressure on echo HRCT "can detect subtle findings that may not be visible on a chest x-ray"; suspected PAH is confirmed by right heart catheterization.
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[Raynaud’s] Nailfold capillaroscopy
Abnormal capillaries suggest secondary Raynaud’s "Abnormal nailfold microscopy is associated with an increased likelihood of developing a CTD, particularly scleroderma."
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[Sjögren’s] Schirmer test
≤ 5 mm wetting in 5 minutes = abnormal A sterile strip inside the lower eyelid measures tear production.
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[Sjögren’s] Anti-SSA (Ro) antibodies
Most sensitive and specific antibody But they "do not alone confirm a diagnosis" and can "be absent in up to one-third of Sjögren cases."
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[Sjögren’s] Minor salivary gland (lip) biopsy
Focal lymphocytic sialadenitis "The minor salivary gland (lip) biopsy remains the most specific single test." Baseline CBC, ESR, chemistry and urinalysis look for complications.
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Musculoskeletal

Fractures, Compartment Syndrome & Fat Embolism
Intracompartmental pressure StatPearls
> 30 mm Hg, or delta pressure (diastolic BP − compartment pressure) ≤ 30 mm Hg = inadequate perfusion → fasciotomy A single normal reading does not exclude the diagnosis — monitor serially or continuously. Thresholds vary by institution (some use ΔP < 20, some absolute > 30 with clinical signs); there is no universal consensus
Normal < 10 mm Hg (range 0–8)
ABG / oxygenation (suspected FES)
Hypoxemia — low PaO₂ with an increased A–a gradient, with tachypnea The respiratory arm of the FES triad; new desaturation 24–72 h post fracture is the trigger to look for the other two arms
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CBC, platelets & ESR (suspected FES) Gurd criteria
Thrombocytopenia, anemia, elevated ESR — Gurd minor criteria, alongside fever > 38.5 °C and tachycardia > 110/min FES diagnosis = 2 major criteria, or 1 major + 4 minor (majors: petechial rash, respiratory insufficiency, cerebral involvement without head injury)
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Chest X-ray (suspected FES)
Diffuse interstitial, flake-like markings — the "snowstorm appearance" Brain MRI is the most sensitive test for cerebral FES
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CT angiography of the chest
Thromboembolism (PE) classically shows a filling defect; FES does not The tiebreaker between FES and PE — V/Q scanning cannot differentiate the two
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CPK (creatine kinase)
Elevated in missed or late compartment syndrome — muscle breakdown (rhabdomyolysis) Rhabdomyolysis threatens the kidneys: watch for acute renal failure after delayed decompression
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Osteoporosis
Dual-energy x-ray absorptiometry (DXA)
Measures bone mineral density in g/cm² at two routine sites — the lumbar spine (L1–L4) and the hip (femoral neck, greater trochanter, Ward’s area, intertrochanteric region and total hip) Radiation "is comparable to standard background radiation." The hip has the strongest correlation with fracture risk; the spine "demonstrates less variability and can detect earlier responses to treatment" but is "prone to interference from surrounding vasculature, calcification, and osteophytes," so expect a falsely high spine reading in an arthritic older adult. Per 1 SD decrease at the femoral neck, hip fracture risk rises 2.6-fold; per 1 SD at the lumbar spine, vertebral fracture risk rises 2.3-fold
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T-score versus Z-score — which patient gets which
T-score compares the patient with a young-adult reference population matched for gender and race; Z-score compares with age-matched controls Using the wrong one misclassifies the patient. A Z-score of −2.0 or lower is below the expected range for that age and should prompt assessment for secondary causes — the single most useful lab signal that something other than aging is at work
Normal T-scores for postmenopausal women and men over 50. Z-scores for premenopausal women, men under 50, and children
WHO T-score categories WHO, as reported by StatPearls
≥ −1.0 normal · between −1.0 and −2.5 osteopenia · ≤ −2.5 osteoporosis · ≤ −2.5 plus a fragility fracture = severe (established) osteoporosis Two reframes the number alone hides. First, more total fractures occur in the osteopenia range (−1.0 to −2.5) than below −2.5, simply because far more people sit there. Second, osteoporosis may also be diagnosed with a T-score between −1.0 and −2.5 when risk-assessment tools demonstrate increased fracture risk — and "regardless of the improvement in the T-score with treatment, the diagnosis of osteoporosis persists"
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Screening — who and when BHOF 2022 Clinician’s Guide; USPSTF 2025 as reported by StatPearls
Women aged ≥ 65 and men aged ≥ 70 regardless of risk factors; postmenopausal women and men aged 50–69 based on risk profile; and any adult who fractures at age 50 or older Those thresholds belong to the Bone Health and Osteoporosis Foundation 2022 Clinician’s Guide — including the recommendation for men, which is BHOF’s, not the USPSTF’s — the USPSTF issues an I statement for men, meaning insufficient evidence to assess the balance of benefits and harms, which is not the same as a recommendation against screening. The USPSTF 2025 update (as reported by StatPearls) adds a Grade B recommendation to screen females younger than 65 with one or more risk factors — weight < 127 lbs, BMI < 21 kg/m², parental hip fracture, current tobacco use, or discontinuing estrogen. Repeat DXA no more often than every 1 to 2 years
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FRAX 10-year fracture risk BHOF 2022 Clinician’s Guide
Treatment thresholds: 10-year hip fracture risk ≥ 3%, or 10-year major osteoporosis-related fracture risk ≥ 20%, in a patient with low bone mass Inputs are age, sex, height, weight, prior fracture, parental hip fracture, tobacco, corticosteroids, rheumatoid arthritis, alcohol, secondary osteoporosis and femoral neck BMD. Know what it misses: it fails to include falls, certain medications linked to low BMD, or diabetes, and does not quantify corticosteroid dose, alcohol or cigarette use, or their duration. A faller with a reassuring FRAX is still a faller
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Baseline and secondary-cause laboratory workup AACE, as reported by StatPearls
CBC; comprehensive metabolic panel including calcium, phosphate, total protein, albumin, alkaline phosphatase, liver enzymes, creatinine and electrolytes; 25-hydroxyvitamin D; and 24-hour urine calcium, sodium and creatinine excretion Targeted additions by context: TSH for hyperthyroidism, intact PTH for hyperparathyroidism, serum protein electrophoresis with kappa/lambda light chains for myeloma, tissue transglutaminase IgA for celiac disease, 24-hour urinary free cortisol for Cushing syndrome, and gonadal hormones for hypogonadism. Vitamin D and calcium must be measured and corrected before an antiresorptive is started, because of hypocalcemia risk
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Vertebral fracture assessment ISCD, as reported by StatPearls
Obtain in a patient with a T-score ≤ −1.0 plus at least one of — female age ≥ 70, height loss ≥ 4 cm, prior vertebral fracture, or corticosteroid ≥ 5 mg prednisone daily for ≥ 3 months Because a third of vertebral fractures are found radiographically rather than clinically, imaging is how the silent ones are caught. For a symptomatic suspected fracture, start with AP and lateral spinal radiographs; MRI distinguishes acute from chronic fractures and identifies malignancy by abnormal marrow signal in pedicles or posterior elements and soft-tissue mass-like extension
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DXA sources of error a nurse can prevent
Artifacts that alter the reported BMD: bra components, surgical clips, navel rings and vascular prostheses — plus positioning error from "excessive internal or external rotation of the proximal femur" Structural change from osteophytes, calcification or an existing fracture "potentially cause an artefactual component of BMD," and demographic-entry errors change the reference population. Practical rule: remove metal before the scan, and read a high spine score in an arthritic patient with suspicion
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Rheumatoid Arthritis RA
Rheumatoid factor (RF)
Antibodies "directed against the Fc portion of IgG," present in 80% to 90% of patients — sensitivity 69%, specificity 85% A positive RF is not a diagnosis. It also appears in Sjögren disease and lupus; in chronic infections — hepatitis C (levels as high as 76%), tuberculosis, subacute infective endocarditis; in sarcoidosis and malignancy; and in up to 4% of young, healthy individuals and older adults. High titres do carry prognostic weight and "probably indicate a poorer prognosis"
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Anti-cyclic citrullinated peptide antibody (anti-CCP / ACPA)
Present in 70% to 80% of patients — sensitivity 67%, specificity 95% This is the specific test, and the better one early: anti-CCP has "similar" sensitivity to RF but "greater specificity than rheumatoid factor for early rheumatoid arthritis." When RF and anti-CCP are both positive, sensitivity and specificity "increase substantially." ACPA positivity also flags the patients at higher risk of interstitial lung disease and increased mortality
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ESR and CRP
"Usually elevated" in active disease; anemia of chronic disease and thrombocytosis are common alongside them An elevated acute phase reactant scores 1 point in the classification criteria. These are also the labs that track response to treatment — and their normality in a painful hand points away from inflammatory arthritis, since blood tests "are usually normal in osteoarthritis"
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2010 ACR/EULAR classification criteria 2010 ACR/EULAR criteria, as reported by StatPearls
6 or more points classifies RA. Joints: 2–10 large = 1 · 1–3 small = 2 · 4–10 small = 3 · more than 10 including ≥ 1 small = 5. Serology: low-positive RF or ACPA = 2 · high-positive = 3. Elevated ESR or CRP = 1. Symptom duration ≥ 6 weeks = 1 The excluded joints are a teaching point in themselves: distal interphalangeal, first carpometacarpal and first metatarsophalangeal — precisely the joints osteoarthritis favours. These are classification criteria; diagnosis remains clinical, supported by testing to rule out other diseases
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Radiographs and MRI
X-ray shows periarticular osteopenia, joint space narrowing, and marginal bony erosions. MRI detects bone marrow edema and synovial thickening MRI findings predict "the future presence of bony erosions" and are useful before radiographic evidence of erosion appears — which is the point, since erosion is irreversible. Contrast with osteoarthritis, which produces marginal osteophytes, subchondral sclerosis and cysts — both narrow the joint space, but only RA erodes and only osteoarthritis grows bone
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Synovial fluid analysis
White cell count between 1,500 and 25,000/mm³, predominantly polymorphonuclear, with low synovial C3 and C4 despite elevated serum levels A count above 25,000/mm³ is rare in rheumatoid arthritis and warrants an infection workup. This is the laboratory half of the hot-red-joint rule — when the joint looks septic, the fluid usually confirms it
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Pre-treatment screening before any DMARD or biologic
Baseline CBC, liver and renal panels, hepatitis B and C serologies, tuberculosis screening, and pregnancy testing Latent tuberculosis must have treatment completed at least 1 month before starting a biologic, and screening precedes TNF inhibitors specifically. This is a hold-the-drug finding, not a paperwork step — and it is one of the clearest places a nurse prevents harm
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Disease-activity measurement ACR 2021 RA treatment guideline
Scored with a validated instrument — CDAI, DAS28-ESR or DAS28-CRP, SDAI or RAPID3 — at every visit that drives a treatment decision Assessment is monthly for moderate-to-severe disease and every 3 to 6 months for low activity or remission. The number is what makes treat-to-target possible: ACR 2021 strongly recommends a treat-to-target approach over usual care, with low disease activity conditionally preferred as the initial goal
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Osteoarthritis & Joint Replacement OA
Laboratory studies StatPearls Primary Osteoarthritis, with the comparison cells cross-checked against the rheumatoid arthritis page
Normal. Complete blood count, erythrocyte sedimentation rate, rheumatoid factor and antinuclear antibody are "usually normal in osteoarthritis." Alkaline phosphatase "may be mildly elevated." C-reactive protein is usually normal "No laboratory test can diagnose osteoarthritis." The laboratory work is run to exclude alternative conditions, not to confirm this one — so a normal panel in a patient with the right history and radiograph supports the diagnosis rather than casting doubt on it
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Rheumatoid factor and anti-CCP StatPearls, Primary Osteoarthritis; comparison cross-checked against the rheumatoid arthritis page
Negative in osteoarthritis — this is the laboratory contrast that separates it from inflammatory arthritis A positive rheumatoid factor in a patient you were calling osteoarthritis is a reason to reconsider the diagnosis, not a reason to add it to the list. The distributions differ too: distal interphalangeal nodes mean osteoarthritis; metacarpophalangeal and proximal interphalangeal synovitis means rheumatoid arthritis
Normal In rheumatoid arthritis, rheumatoid factor or anti-citrullinated peptide antibody is positive and the inflammatory markers are elevated
Plain radiography StatPearls Primary Osteoarthritis, with the comparison cells cross-checked against the rheumatoid arthritis page
Four findings: marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts. Erosive hand osteoarthritis adds subchondral erosions Both conditions narrow the joint space. Only rheumatoid arthritis erodes, and only osteoarthritis grows osteophytes — that pair is the discriminator, not the narrowing. The radiographic changes are graded, but this page does not name a grading system, because none of its sources does
Normal Rheumatoid arthritis shows periarticular osteopenia, joint space narrowing and marginal erosions
Imaging selection StatPearls, Primary Osteoarthritis
Plain radiography is "the most commonly used modality in clinical practice" (EULAR calls it the gold standard for initial knee and hand assessment). MRI "may be helpful in patients with an uncertain diagnosis." Ultrasound is used for peripheral joints Radiographic disease far outruns symptomatic disease — 19.2% of adults over 45, 37% over 60, 80% over 75 — so an abnormal film does not establish that the film explains the pain, and a mild film does not mean the pain is not real. The x-ray is not the patient, in either direction
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Making the diagnosis MedlinePlus, Osteoarthritis
Clinical and radiographic — no single test makes the diagnosis — history, examination, imaging and laboratory work are combined, with the laboratory work used to "exclude inflammatory conditions such as rheumatoid arthritis" The practical consequence for a nurse taking the history: the questions that carry diagnostic weight are how long the morning stiffness lasts, whether rest helps, and which joints are involved. Those three answers do more than any test on this page
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Synovial fluid analysis Synovial fluid in osteoarthritis is non-inflammatory; the rheumatoid arthritis page owns the cell-count thresholds
Non-inflammatory in osteoarthritis The inflammatory counterpart and the cell-count thresholds — including the count above which an infection workup is warranted — belong to the rheumatoid arthritis page. Aspiration here is used mainly to exclude crystal disease and infection when the joint is unexpectedly hot
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Post-arthroplasty neurovascular assessment Post-arthroplasty neurovascular assessment; the operative detail belongs to the surgical team
After any arthroplasty, motor function, sensation and perfusion distal to the joint, checked against the preoperative baseline rather than against how the limb looks This is a scheduled check rather than a response to a complaint, because a fresh postoperative limb is expected to feel abnormal and the patient will not reliably distinguish nerve injury from normal swelling and analgesia
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Postoperative mobility orders Surgeon's operative orders
Whatever the surgeon has written. This page prints no range-of-motion target, no weight-bearing rule and no day-by-day schedule The silence is deliberate and it is worth stating: the knee-arthroplasty literature that carries those figures sits outside this page's source list, and a hip figure must not be relabelled as a knee one. Ask for the order; do not supply a default from memory
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Gout
Arthrocentesis with compensated polarized light microscopy
NEEDLE-SHAPED, NEGATIVELY BIREFRINGENT crystals, "often INTRACELLULAR, indicating ACTIVE PHAGOCYTOSIS." The fluid in a flare is "typically YELLOW AND CLOUDY, containing crystals and white blood cells, predominantly NEUTROPHILS" This is the gold standard — "MSU CRYSTAL IDENTIFICATION REMAINS THE GOLD STANDARD FOR DIAGNOSING GOUT." Arthrocentesis is "ESSENTIAL to confirm the diagnosis and differentiate it from other conditions such as SEPTIC ARTHRITIS, LYME DISEASE, or PSEUDOGOUT (caused by CALCIUM PYROPHOSPHATE crystals)." And the technique also works between attacks — it "can also identify uric acid crystals from tophaceous deposits AND JOINTS DURING THE INTERCRITICAL PERIOD," which is how the intercritical stage is proved rather than assumed.
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Gram stain, culture and synovial glucose — sent on the same sample
In septic arthritis the fluid is "MORE OPAQUE, with a YELLOW-GREEN appearance," with "a HIGHER WBC COUNT (> 50,000/microL)" and neutrophil predominance, and "POSITIVE SYNOVIAL FLUID GRAM STAINS AND CULTURES, along with LOW SYNOVIAL FLUID GLUCOSE" ❗ Read the caveats, because they overturn the usual shortcut. "THERE IS CONSIDERABLE OVERLAP IN WBC COUNTS AND NEUTROPHIL PERCENTAGES between patients with acute gouty arthritis and those with septic arthritis, RENDERING THESE PARAMETERS UNRELIABLE for diagnosis." And decisively: "IT IS ESSENTIAL TO NOTE THAT THE PRESENCE OF CRYSTALS IN SYNOVIAL FLUID ANALYSIS DOES NOT RULE OUT SEPTIC ARTHRITIS, AS BOTH CONDITIONS CAN COEXIST" — corroborated elsewhere as "multiple etiologies can co-exist, and the presence of gout does not rule out the presence of concomitant infection." Send the Gram stain and culture regardless of what the crystals show.
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Serum uric acid — during a flare
"During acute gouty arthritis, the serum urate level may be HIGH, NORMAL, OR LOW. Approximately 50% OF PATIENTS WITH ACUTE GOUTY ARTHRITIS DO NOT HAVE AN ELEVATED SERUM URIC ACID LEVEL" ❗❗ The most examinable diagnostic fact on this page, and the source states it as a rule: "SERUM URIC ACID MEASUREMENT DURING AN ACUTE ATTACK IS OF NO DIAGNOSTIC VALUE; IT IS MOST USEFUL WHEN CHECKED AFTER THE RESOLUTION OF THE FLARE." So a normal level does not exclude gout and a high level does not confirm it — remember that hyperuricemia "does not cause health problems for everyone." The serum urate has a different job entirely, further down this page: it is the treat-to-target monitoring value once urate-lowering therapy starts.
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White cell count, ESR and C-reactive protein
"Elevations in the WBC count, erythrocyte sedimentation rate, and C-reactive protein levels during acute gouty arthritis" "These features are NONSPECIFIC and DO NOT CONFIRM OR DIFFERENTIATE the diagnosis from SEPTIC ARTHRITIS." They tell you the joint is inflamed, which the bedside already told you. The inflammatory markers and their kinetics are owned by the inflammation page; here their role is simply that they cannot settle the question the aspiration settles.
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Joint x-ray
Radiographs "may show gouty erosions," often described as "rat bite" or "punched-out" erosions with thin overhanging edges; ultrasonography and dual-energy CT can assist Imaging supports the diagnosis; it does not replace the aspiration. And when radiographic damage attributable to gout is present by any imaging modality, that finding is by itself a strong ACR indication to start urate-lowering therapy.
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Urinary uric acid crystals and urine pH
"Urinary uric acid will form crystals if urine pH is ACIDIC (< 5.5). These YELLOWISH-BROWN crystals can be RHOMBOID or cluster to create a ROSETTE shape" Different crystal shape, different organ, same chemistry. Gout and uric acid nephrolithiasis are named as "the 2 most common complaints associated with hyperuricemia," and uric acid stones result "from the accumulation of uric acid crystals in the kidneys," which "often correlates with elevated uric acid levels in the bloodstream." Urolithiasis is also one of the conditional ACR indications to start urate-lowering therapy even after a first flare.
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Arthrocentesis — the procedure itself
Synovial fluid "collected by penetrating the joint space through aspiration… under STERILE procedural conditions," because "sterility is essential NOT ONLY to prevent transmission of infection BUT ALSO to ensure accurate fluid analysis" Two practical limits to expect. "Unsuccessful aspiration is COMMON, as synovium can CLOG THE NEEDLE," and "nonsterile technique can contaminate the collected fluid" — which matters doubly here, because a contaminated sample cannot answer the septic-arthritis question. Complications are "rare, and those that do occur are typically not severe": seeding a skin infection into the joint, rare cartilage damage, pain or local ecchymosis at the site, bleeding and iatrogenic haemarthrosis, and skin reaction to antiseptic or dressing adhesive.
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Osteomyelitis Bone infection
CRP and ESR
Often raised; in vertebral osteomyelitis 94–100% sensitive. Diabetic-foot screening (StatPearls): CRP > 10 and ESR > 40 (units not given in the source) CRP tracks the response to treatment — trend it through the course.
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White blood cell count
May or may not be raised — up to 40% of vertebral osteomyelitis patients have a normal WBC A normal WBC does not rule out osteomyelitis.
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Blood cultures
May be positive, especially in hematogenous vertebral, clavicular or pubic infection In a stable patient with suspected vertebral osteomyelitis (not septic, no neurologic deficit), antibiotics wait for blood culture results. S. aureus bacteremia in the past 3 months with a compatible spine MRI is treated as vertebral osteomyelitis without further sampling.
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Plain X-ray
Usually the first image, but findings may lag about 14 days — in the diabetic foot, StatPearls notes "X-ray findings of osteomyelitis take 4 to 6 weeks to develop"; lytic change appears only after 50–75% of bone matrix is lost A normal early X-ray does not exclude osteomyelitis.
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MRI
Highest combined sensitivity and specificity; detects infection within 3 to 5 days of onset; preferred for spinal infection (accuracy over 90%) Limited by surgical hardware — nuclear imaging is sensitive but poorly specific and useful when metal prevents MRI.
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Bone biopsy (open or percutaneous)
Establishes the diagnosis, the organism and its susceptibilities Ideally before antibiotics to raise the yield. Superficial wound swabs, needle punctures and sinus-tract material correlate poorly with bone results — deep tissue or bone cultures guide treatment.
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Low Back Pain & Herniated Disc LBP
History and neurological examination
Pain description and what makes it better or worse; reflexes, muscle strength, sensation; straight-leg raise; heel and toe walking "A focused neurological history should assess bladder and bowel function and document any perineal or perianal sensory loss." NIAMS: "Most people do not need additional testing"
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Imaging — not early, unless there are red flags
Indicated for back pain persisting longer than 6 weeks despite conservative management, or at once for red flags "Early imaging in adults has been associated with poorer outcomes, as it often leads to more invasive interventions that provide minimal benefit." Findings must be read with caution — "Disc degeneration occurs in more than 80% of adults older than 50"
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MRI
The gold standard for a suspected disc herniation (diagnostic accuracy 97%) and for nerves and soft tissue CT myelography if MRI is contraindicated. X-rays show only bone — for fractures
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Urgent MRI and bladder scan — suspected cauda equina
"The gold standard method of evaluation for CMS/CES is obtaining urgent MRI imaging" — "An ideal goal for MRI is one hour from the patient presentation" "A bladder scan checking for a post-void residual volume should also be obtained to evaluate for urinary retention." Exam may show absent or decreased rectal tone, a palpable bladder and saddle anesthesia
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Blood tests — only for red flags
ESR or CRP, complete blood count Justified when "fever, night pain, unexplained weight loss, persistent rest pain, or progressive neurologic deficit raise suspicion for infection, malignancy, or inflammatory spondyloarthropathy"
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Amputation Care Limb amputation
Serial stump and wound assessment
Healing edges without necrosis, bleeding or infection "the limb stump should be serially examined every 24 to 48 hours for necrosis of the skin edges, bleeding, and signs of infection" (StatPearls).
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Hemoglobin and hematocrit
Monitored after surgery for blood loss "Hemoglobin and hematocrit are also monitored postoperatively due to blood loss."
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Doppler ultrasound
Blood flow to the residual limb "Doppler ultrasound may be used to assess vascular status and blood flow to the residual extremity."
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Pre-operative bedside assessment of healing potential
Pulses, temperature, hair growth; a femoral pulse supports a below-knee level "Despite many available modalities for assessing healing potential, none has proven more useful than a good physical exam."
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Fibromyalgia FM
Widespread Pain Index + Symptom Severity scale (2016 criteria) StatPearls, describing ACR 2010/2016
WPI 7 or more with SS 5 or more, or WPI 4–6 with SS 9 or more; pain in 4 of 5 regions; symptoms for at least 3 months As described by StatPearls from the ACR 2016 revision. The 1990 count of tender points is historical and no longer used for diagnosis.
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Physical exam
Soft-tissue tenderness greater than joint tenderness; no synovitis "Clinicians should palpate multiple soft tissue sites and joints, noting greater tenderness in the soft tissues and the absence of synovitis." NIAMS: the doctor examines the joints for another condition "such as rheumatoid arthritis or systemic lupus erythematosus (lupus)."
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Basic labs and imaging
Typically normal NIAMS: "Currently, there are no specific laboratory or imaging tests for fibromyalgia." Tests rule out look-alikes — the StatPearls differential includes polymyalgia rheumatica, hypothyroidism, systemic lupus erythematosus, vitamin B12 deficiency and vitamin D deficiency.
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Screening for sleep and mood disorders
Sleep apnea, restless legs, depression, anxiety "Clinicians should screen patients for sleep apnea and restless leg syndrome, referring those with suspected primary sleep disorders to sleep medicine." Depression, anxiety and sleep disorders "can exacerbate one another."
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[SAV] Blood pressure and heart rate before and during milnacipran SAVELLA label
Baseline and periodic readings "SAVELLA may increase blood pressure and heart rate. Measure blood pressure and heart rate prior to initiating treatment with SAVELLA and monitor periodically throughout treatment."
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Integumentary

Burns
%TBSA estimate (rule of nines / Lund-Browder) StatPearls (Parkland Formula; Burn Fluid Resuscitation)
Partial- and full-thickness area only — superficial burns are excluded. Adults with more than 20% TBSA need formula-driven fluid resuscitation (more than 10% in children) Use the age-adjusted Lund-Browder chart for children — the adult nines misallocate their proportions. Estimates tend to run high.
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Carboxyhemoglobin (CO-oximetry) StatPearls
Significant poisoning at > 20% in adults (> 15% in children); levels correlate poorly with symptoms Standard pulse oximetry cannot see it — SpO₂ reads falsely normal because the device cannot distinguish carboxyhemoglobin from oxyhemoglobin. A blood gas with co-oximetry is required.
Normal < 3% nonsmokers · up to ~10% smokers
Hourly urine output (indwelling catheter) StatPearls
The resuscitation-adequacy gauge: titrate fluids to 0.5–1.0 mL/kg/h in adults (≈ 30–50 mL/h) · 1.0–1.5 mL/kg/h in children · 1–2 mL/kg/h after electrical injury The formula predicts; the urine decides. Cross-check with SBP > 90 mm Hg, base deficit, and lactate clearance — no single number is worshipped.
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Bronchoscopy
Direct visualization of airway injury — with carboxyhemoglobin, the key test for inhalation injury
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ECG + cardiac monitoring
Peaked T waves of early hyperkalemia; after electrical injury, every adult gets an ECG and monitoring — ventricular fibrillation can occur at currents as low as 50–120 mA New abnormalities are unlikely to first appear after 24–48 h of clean monitoring.
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CK, electrolytes/creatinine, urinalysis (electrical burns)
Rhabdomyolysis screen: elevated CK; urine dipstick positive for "blood" with no RBCs on microscopy = myoglobin; add troponin when current crossed the chest
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Pressure Injuries
Braden Scale Braden / AHRQ
≤ 18 = at risk. Bands: 15–18 mild · 13–14 moderate · 10–12 high · ≤ 9 very high risk Score on admission, then every 24 hours in acute care. Six subscales (sensory perception, moisture, activity, mobility, nutrition, friction/shear) — interventions target the deficient subscale, not just the total
Normal Total range 6–23 — lower = higher risk
Blanching test (fingertip pressure over erythema) NPUAP/NPIAP 2016
Non-blanchable — the reddened area does not turn white when pressed A teaching variant: redness that persists > 30 minutes after pressure is relieved is treated as Stage 1. On darker skin tones, palpate for warmth, coolness, or bogginess instead of relying on color
Normal Healthy or reactive erythema blanches, then refills
Wound measurement & documentation
Length × width × depth plus the extent of any undermining and tunneling, at every assessment Also record wound-bed tissue (granulation/slough/eschar), exudate type (serous, serosanguineous, sanguineous, purulent) and amount, edges, periwound skin, odor, and pain — with photographs for the record
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Serum albumin AHRQ
< 3.5 g/dL predisposes to increased pressure-injury risk Current protein intake predicts risk more independently than the lab value — a normal albumin does not excuse a poor diet history
Normal ≥ 3.5 g/dL
Wound culture AHRQ
A wound is considered infected at ≥ 10⁵–10⁶ organisms per gram of tissue — and healing stalls until the microbial load is controlled Collect per agency policy when infection signs appear; notify the provider of new infection signs or lack of healing progress
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Osteomyelitis workup (deep, non-healing injuries) StatPearls
MRI is most sensitive (78–90%, detects changes within 3–5 days); plain X-ray lags ~14 days; bone biopsy/culture is the gold standard A blunt sterile probe that reaches bone (probe-to-bone test) is highly suggestive. CRP tracks treatment response
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Wound Healing & Wound Infection Surgical site infection
Wound assessment StatPearls, Wound Assessment
Measure depth, length and width, and measure the amount of undermining and tunneling. Describe tissue type, exudate type and amount, periwound skin, and infection signs The assessment is the diagnostic in this disorder — and the pressure-injury page owns the documentation standard and the tissue vocabulary this assessment uses. Note two deliberate gaps: the fetched chapter instructs you to measure undermining and tunneling without defining either term, and it gives no clock-face convention. The fuller documentation standard, including photographs and odour, belongs to the pressure-injury page
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Wound-bed tissue and exudate vocabulary StatPearls, Wound Assessment
Granulation — "beefy red bleeding tissue that indicates healing in progress." Slough — "white-ish/yellow slough that does not bleed (not healthy)." Eschar — "black/charred-appearing callous-like tissue (not healthy)" The four exudate types are listed but not defined in the fetched source, so the vocabulary is taught as vocabulary and no invented definitions are supplied. The same three tissue descriptions appear on the pressure-injury page, and the two agree
Normal Exudate types: serous, serosanguineous, sanguineous, purulent. Amount: minimal, light, moderate, heavy
Wound culture — the Levine technique International Wound Journal, 2011 — the validating study
The Levine technique "involves rotating the wound swab over a 1-cm(2) area of the wound." The comparator, the Z technique, "involves rotating the swab between the fingers in a zigzag fashion across the wound without touching the wound edge" The preparatory step is part of the technique: cleanse the wound with normal saline and wipe off surface contaminants before swabbing (Open RN wound-culture checklist). Swabbing the pus on top cultures the surface, not the tissue. Culture technique is what this page owns; the decision about when to culture is a management one made with the team
Normal The Levine technique "detected significantly more organisms than the Z technique (P≤ 0· 001)" — the authors attribute this to its "ability to express fluid from the wound bed"
Superficial incisional SSI criteria CDC NHSN Patient Safety Component Manual, chapter 9, January 2026
Within 30 days of the procedure (day 1 = the procedure date), involving only skin and subcutaneous tissue, plus at least one of: purulent drainage; organisms from an aseptically obtained specimen; a deliberately opened, re-accessed or aspirated incision with antimicrobial therapy for at least 2 calendar days and new or worsening localized pain, swelling, erythema or heat; or a physician diagnosis Superficial incisional SSIs are monitored for 30 days for ALL procedure categories — there is no 90-day version of a superficial event, which is the part the common shorthand loses
Normal Superficial events are more than 50% of all SSIs
Deep incisional and organ/space SSI criteria CDC NHSN Patient Safety Component Manual, chapter 9, January 2026
Deep incisional involves deep soft tissues of the incision, for example fascial and muscle layers, and its criteria explicitly include an incision that spontaneously dehisces. Organ/space involves tissues "deeper than the fascia/muscle," evidenced by purulent drainage from a drain placed into the organ space, organisms from organ-space fluid or tissue, or an abscess on examination, histopathology or imaging The 90-day list is a named procedure list, not a set of specialties: breast surgery, cardiac surgery, coronary artery bypass graft, craniotomy, spinal fusion, open reduction of fracture, herniorrhaphy, hip prosthesis, knee prosthesis, pacemaker surgery, peripheral vascular bypass and ventricular shunt. Colon surgery, appendectomy, cesarean section, hysterectomy and laparotomy are all 30 days
Normal Window: 30 or 90 days according to the NHSN procedure list
Surgical wound class CDC NHSN, January 2026 — which assigns wound class but does not define what each class contains
Four class names, describing the operation in rising order of expected contamination: clean, clean-contaminated, contaminated, dirty or infected Wound class is assigned in the operating room "by a person involved in the surgical procedure," and NHSN states it "does not offer guidance on which wound class should be assigned" — so the description of what each class contains is relayed from StatPearls rather than defined by NHSN. It describes the operation; SSI depth describes the infection
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Imaging and microbiology in SSI CDC NHSN, January 2026, for the depth definitions and windows
Diagnosis is primarily clinical evaluation. Imaging — ultrasound, CT or MRI — is indicated for suspected deep or organ-space infections; CT evidence of abscess is itself a deep incisional criterion There is a rising prevalence of methicillin-resistant S. aureus and extended-spectrum beta-lactamase organisms, attributed to inappropriate broad-spectrum antibiotic use. SSIs are the leading cause of unplanned postoperative readmission
Normal The likely organism follows the operative site — skin flora after procedures that do not enter a hollow viscus, and bowel flora after those that do
Bite-wound microbiology StatPearls, Animal Bites
From cats, Pasteurella multocida is the most commonly isolated pathogen, plus anaerobes. From dogs, Pasteurella canis. In immunocompromised patients, Capnocytophaga canimorsus, "a gram-negative bacterium commonly found in the canine oral cavity" The organism list is the justification for the drug: mixed aerobes and anaerobes are why amoxicillin-clavulanate rather than amoxicillin is preferred. Tetanus (CDC): a bite is a dirty wound — vaccinate if the history is unknown or the primary series incomplete, or if the last dose was 5 or more years ago; tetanus immune globulin is added only for unknown or incomplete vaccination, HIV, or severe immunodeficiency. Rabies prophylaxis is immediate "for bites near the brain"
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Cellulitis & Necrotizing Fasciitis Erysipelas
Diagnosis of cellulitis StatPearls, Cellulitis
Clinical. "Cellulitis is diagnosed clinically based on spreading erythematous inflammation of the deep dermis and subcutaneous tissue," requiring two of the four criteria: warmth, erythema, edema, or tenderness Cellulitis is common — about 50 cases per 1,000 patient-years, over 14 million US cases annually, 650,000 hospitalizations. That frequency is also why the mimics matter: many conditions look similar, and the sourced safeguard is the 48-hour reassessment rather than a confirmatory test
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Blood cultures StatPearls, Cellulitis
Not routine. "Consider blood cultures only in patients who are immunocompromised, have experienced an immersion injury, or have had animal bites," or who have signs of systemic infection The temptation to culture everything is strong in an infection this common, and the yield does not justify it. For Fournier gangrene the workup is different and broader: complete blood count, metabolic panel, lactate, and blood cultures
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Imaging in cellulitis IDSA, as reported by StatPearls
Not routine either. The IDSA practice guidelines "recommend against imaging the infected area except in patients with febrile neutropenia" Imaging has one clear role in this disorder family, and it is not in uncomplicated cellulitis: it is to confirm a suspected deep vein thrombosis, which requires ultrasound confirmation. The discriminator that prompts that scan is systemic — DVT "rarely manifests with fevers or leukocytosis"
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LRINEC score components StatPearls, Necrotizing Fasciitis
C-reactive protein under 150 mg/L = 0, over 150 = 4. White cells under 15 = 0, 15 to 25 = 1, over 25 = 2. Hemoglobin over 13.5 g/dL = 0, 11 to 13.5 = 1, under 11 = 2. Sodium 135 mmol/L or above = 0, under 135 = 2. Creatinine 1.6 mg/dL or less = 0, over 1.6 = 2. Glucose 180 mg/dL or less = 0, over 180 = 1 The limitation is the reason to teach the score at all: "the diagnosis of NSTIs is still primarily clinical," and "no lab or imaging test should delay surgical intervention." A low score in a patient with pain out of proportion does not rule this out
Normal A score of 6 has a positive predictive value of 92% and a negative predictive value of 96%. A score of 8 or greater represents a 75% risk of necrotizing infection
Imaging in necrotizing infection StatPearls, Necrotizing Fasciitis and Fournier Gangrene
CT offers "greater sensitivity than plain film," and plain X-rays have "no value. For Fournier gangrene, CT has 88.5% sensitivity and 93.3% specificity, showing fat stranding, emphysema, fascial thickening"; ultrasound detects subcutaneous gas (pathognomonic finding) The same rule governs all of it: imaging should never delay surgery in obvious cases, and "no lab or imaging test should delay surgical intervention." Imaging is for the uncertain case, never for the convinced one
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The finger test StatPearls, Necrotizing Fasciitis
"Sometimes, under local anesthesia, one may probe the area with a finger for signs of necrotizing tissue. In most cases, the necrotic tissue can be penetrated with little resistance" This is the sourced operative finding, and it is worth knowing because a more colourful phrase is widely taught in its place. No source fetched for this page uses the words "dishwater" or "dirty dishwater fluid," so that description is not used here. Histopathology shows "extensive superficial fascial necrosis" with thrombosed vessels
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Distinguishing the mimics StatPearls, Cellulitis
Deep vein thrombosis — unilateral "tenderness, erythema, warmth, and edema" but it "rarely manifests with fevers or leukocytosis," and needs ultrasound. Venous stasis dermatitis — "a long-standing, bilateral, inflammatory dermatosis" of the medial malleoli with "erythema with scaling, peripheral edema, and hyperpigmentation." Contact dermatitis is also on the list Bilateral plus chronic plus scaling plus hyperpigmented equals stasis dermatitis, not cellulitis — and treating stasis dermatitis with antibiotics is a common error. Note what is deliberately not quantified here: no fetched source gives a percentage for how often cellulitis is misdiagnosed, so none is stated
Normal Cellulitis is unilateral, acute, flat-edged and febrile in moderate-to-severe cases
Admission criteria for cellulitis StatPearls, Cellulitis
Admit for "2 or more systemic inflammatory response criteria" — fever above 38 °C, heart rate above 90, respiratory rate above 20, white cell count above 12,000/mm3, white cell count below 4,000/mm3, or bandemia of 10% or more The sepsis page owns the generic SIRS criteria and the Sepsis-3 definitions
Normal Also consider admission for failed outpatient treatment, immunocompromise, rapidly progressing erythema, inability to tolerate oral medications, or cellulitis near an indwelling device
Skin Cancers Basal cell carcinoma
Whole-body skin examination
Identifies suspicious lesions and other nevi for comparison ("ugly duckling") "A whole-body skin examination is the most essential and fundamental evaluation needed in diagnosing melanoma, and it should be performed in the presence of optimal lighting." Include nail units and all lymph node groups
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Skin biopsy NCI PDQ
Histology confirms BCC, SCC or melanoma Shave or punch is usually sufficient for BCC and SCC; suspected melanoma = excisional biopsy — "Suspicious lesions should never be shaved off or cauterized"
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Melanoma thickness (Breslow depth) and ulceration
Thicker lesions and ulceration = worse prognosis; they drive AJCC staging and excision margins Excision margins widen with thickness (0.5–1 cm for in situ up to 2 cm for > 2 mm)
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Sentinel lymph node biopsy
Detects regional node spread in melanoma Recommended "in melanomas with T1b or higher staging." After a positive node, observation with nodal ultrasound "has widely replaced complete lymph node dissection"
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Melanoma labs and imaging
CBC, chemistry with liver tests, LDH; imaging (chest X-ray, brain MRI, CT, PET-CT, nodal ultrasound) when indicated Imaging is considered for melanoma; metastatic BCC is "exceedingly rare"
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BRAF V600 testing
Mutated in about 40% to 50% of cutaneous melanomas Determines eligibility for BRAF/MEK inhibitors
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Psoriasis & Chronic Dermatitis Psoriasis
Skin, scalp and nail examination
Psoriasis is diagnosed clinically; a small skin biopsy only if another condition could look the same. "Histopathology is rarely necessary" in psoriasis.
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Cardiometabolic screen in psoriasis
Screen for type 2 diabetes, hypertension and dyslipidemia. Psoriasis raises the risk of heart attack, stroke, diabetes and metabolic syndrome.
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Tuberculosis and hepatitis screening before a biologic
Completed before the first dose. "Before starting any biological agent, the patient should be worked up for tuberculosis and hepatitis." Monitor routine blood, liver and renal function on systemic therapy.
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Patch testing (allergic contact dermatitis)
A positive reaction identifies the allergen. "Patch testing is considered to be the gold standard in diagnosing contact allergic dermatitis" — patches off at 48 hours, final read 48–72 hours later.
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HPA-axis evaluation on a topical steroid
Suppression is possible with large areas or occlusion. "Patients applying a topical steroid to a large surface area or to areas under occlusion should be evaluated periodically for evidence of HPA axis suppression."
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Herpes Zoster (Shingles) & Postherpetic Neuralgia Shingles
[Shingles] Clinical diagnosis
Painful dermatomal vesicular rash "The signs and symptoms of herpes zoster are usually distinctive enough to make an accurate clinical diagnosis once the rash appears." Diagnosis is hard without a rash and in children and younger adults.
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[Shingles] PCR for VZV DNA CDC
Positive from vesicle fluid (or corneal lesions / blood when ocular or disseminated) "Polymerase chain reaction (PCR) is the most helpful laboratory test for confirming cases of herpes zoster." The Tzanck smear "has lower sensitivity and specificity."
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[HZO] Eye examination
Conjunctivitis, keratitis, uveitis, episcleritis or retinitis "When eye involvement is present, patients must be referred promptly to an ophthalmologist." CT/MRI when orbital cellulitis, intracranial spread or vasculopathy is suspected.
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[PHN] Clinical diagnosis CDC definition
Pain in the old rash area more than 90 days after onset "the diagnosis of postherpetic neuralgia (PHN) is relatively straightforward and is not a diagnosis of exclusion."
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[Valacyclovir] Renal function in older adults FDA label (Valtrex)
Dose adjusted to creatinine clearance Label: "reduce dosage in patients with renal impairment"; StatPearls: "Monitor serum creatinine and electrolytes in older adults and immunocompromised individuals."
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Stevens-Johnson Syndrome & Toxic Epidermal Necrolysis SJS/TEN
Clinical picture + early skin biopsy
Full-thickness epidermal necrosis at the dermo-epidermal junction "Early skin biopsy confirms the diagnosis and guides the treatment plan." There are "no standard diagnostic criteria"; targetoid lesions, two mucous membranes and a recent drug are suggestive.
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Body surface area detached or detachable
<10% SJS · 10–30% overlap · >30% TEN Count detachable (Nikolsky-positive) and detached epidermis — not erythema alone.
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Drug timeline
Culprit usually started 4–28 days before onset "Causality is primarily determined through careful history-taking and construction of a drug timeline, including prescription drugs, over-the-counter medications, and supplements." Drug rechallenge "is contraindicated."
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Screening labs — CBC, electrolytes, BUN, bicarbonate, glucose, liver tests, coagulation, arterial blood gas
No diagnostic blood test; anemia and lymphopenia common; neutropenia is unfavorable Guide supportive care and SCORTEN. Electrolytes, glucose and fluid balance "should be monitored daily" (Shah 2024, citing SDH).
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SCORTEN StatPearls
7 variables: age over 40, cancer, tachycardia, detached BSA 10% or more, high BUN, low bicarbonate, high glucose Assess within 24 hours and again on day 3; mortality ranges "from 3.2% if only 1 risk factor is present to greater than 90% if 5 or more risk factors are present." Guides ICU or burn-unit placement.
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Skin, urine and blood cultures
Detect infection early StatPearls (citing SDH): skin microbiology "on the day of presentation and every 48 hours."
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[Carbamazepine] HLA-B*1502 before starting (at-risk ancestry) FDA label (Tegretol)
Test before starting; positive → avoid unless benefit clearly outweighs risk "PATIENTS WITH ANCESTRY IN GENETICALLY AT-RISK POPULATIONS SHOULD BE SCREENED FOR THE PRESENCE OF HLA-B*1502 PRIOR TO INITIATING TREATMENT WITH TEGRETOL." Screening "must never substitute for appropriate clinical vigilance."
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[Allopurinol] HLA-B*58:01 in high-prevalence populations FDA label (allopurinol)
Consider before starting "Consider screening for HLA-B*5801 before starting treatment with Allopurinol Tablets in patients from populations in which the prevalence of this HLA-B*5801 allele is known to be high." SJS/TEN "can still occur in patients who are found to be negative."
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Reproductive & OB

Preeclampsia, Eclampsia & HELLP HELLP
Blood pressure StatPearls
≥ 140/90 on 2 occasions ≥ 4 h apart after 20 weeks = diagnostic; ≥ 160/110 = severe range (may be confirmed on readings minutes apart to expedite treatment) Persistent severe-range pressure lasting ≥ 15 minutes is the treatment trigger — do not wait 4 hours to "confirm" a 160/110
Normal < 140/90
Urine protein StatPearls
≥ 300 mg on 24-h collection, protein/creatinine ratio ≥ 0.3, or dipstick ≥ 2+ The dipstick is the least reliable method — used when quantitative testing is unavailable. Proteinuria is not required for the diagnosis when new maternal organ dysfunction is present.
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Platelet count StatPearls
< 100 K/mm³ = severe feature — and one arm of the HELLP triad Falling platelets in a preeclamptic patient means the microvasculature is consuming them — recheck, don’t wait
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Serum creatinine StatPearls
≥ 1.1 mg/dL or doubling of baseline = severe feature Doubles as the magnesium-safety lab: magnesium is renally cleared, so a rising creatinine raises toxicity risk on a standard infusion
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AST/ALT + hemolysis panel Tennessee classification
Transaminases > 2× ULN = severe feature. HELLP = hemolysis (≥ 2 of: schistocytes/burr cells on smear, bilirubin > 1.2 mg/dL, haptoglobin < 25 mg/dL or LDH > 2× ULN, hemoglobin < 8–10 g/dL) + AST or ALT > 2× ULN + platelets < 100,000/µL Order the panel for third-trimester RUQ/epigastric pain regardless of the BP
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Serum magnesium (on therapy) StatPearls
Therapeutic for seizure prophylaxis: 4–7 mEq/L (2.0–3.5 mmol/L); DTRs lost at 8–10 · respiratory depression at 10–15 · cardiac arrest at 25–30 mEq/L Levels every 6–8 h or clinical checks of patellar reflexes and urine output — and remember that the kidney clears it
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Postpartum Hemorrhage PPH
Quantified blood loss (QBL) Open RN (definition); WHO 2023 (measurement)
≥ 1,000 mL total — or blood loss with hypovolemia signs — within 24 h after birth = PPH WHO recommends routine objective measurement for every birth: graduated under-buttock drapes, and weighing pads/chux — 1 gram of blood = 1 mL of blood loss. Visual estimation is frequently inaccurate (it underestimates), so PPH goes unrecognized or is caught too late. Quantified methods, though more accurate, have not consistently improved outcomes on their own — keep assessing the patient, not just the number.
Normal Traditionally defined as > 500 mL at a vaginal delivery or > 1,000 mL at a cesarean
Treatment trigger WHO 2023
First-response bundle initiated at measured loss ≥ 500 mL, or ≥ 300 mL with early warning signs of excessive blood loss Don’t wait for the 1,000-mL definition to be met before acting — the trigger is deliberately earlier than the diagnosis.
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Fundal assessment (height + tone)
Boggy, soft, unusually enlarged uterus with bleeding from the cervical os = atony; fundal height above the expected level or displaced from midline = distended bladder. Expected course, as described in a 2024 involution trial: midway between symphysis and umbilicus right after delivery, rising to just above or below the umbilicus within about 12 hours, then descending about 1 cm per day The first 1–3 h after delivery (fourth stage) is when the patient is closely monitored for complications — palpate fundal location and tone, and have her empty her bladder before massage.
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Vital-sign trend
Tachycardia and tachypnea first, narrowed pulse pressure, delayed capillary refill; hypotension only after ≈ ≥ 1,500 mL lost Trend the heart rate against its own baseline — pregnancy hypervolemia can hide > 1,000 mL of loss behind normal-looking numbers.
Normal BP can run slightly high in the immediate postpartum period (pain, anxiety, fluid shifts)
Placental inspection
Placenta not intact → retained placental tissue (the Tissue arm) The delivered placenta "should be examined to determine if the tissue remains intact," and a manual examination with extraction is performed for any retained placental tissue; a bedside ultrasound may be part of the evaluation. A third stage > 30 minutes raises PPH risk and may indicate the need for manual removal.
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Pelvic ultrasound
An echogenic mass within the endometrial cavity immediately after delivery is consistent with retained placenta Useful when bleeding persists and the placenta looked incomplete — or in secondary PPH workup.
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Gestational Diabetes GDM
50 g glucose challenge test (two-step, step 1) USPSTF 2021 (two-step process, 130–140 mg/dL); StatPearls (the three cut-offs)
Plasma glucose at 1 hour; positive at 130, 135 or 140 mg/dL or above, depending on the institution's protocol The patient does not fast for this one, and a positive result is not a diagnosis — it is the trigger for the 3-hour test. Three cut-offs are in simultaneous use and the sources present them as alternatives, not as a progression; teach all three and use the local protocol
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100 g 3-hour OGTT (two-step, step 2) Carpenter-Coustan and NDDG thresholds as printed in USPSTF 2021, Table 2
Carpenter-Coustan: fasting 95, 1-hour 180, 2-hour 155, 3-hour 140 mg/dL. Two or more abnormal values diagnose GDM Fasting test. Because two threshold sets exist for one test, a value can be normal by NDDG and abnormal by Carpenter-Coustan — always name the criteria set with the number
Normal Older NDDG thresholds for the identical test are higher — 105 / 190 / 165 / 145 mg/dL, also requiring two abnormal values
75 g 2-hour OGTT (one-step) IADPSG thresholds as printed in USPSTF 2021, Table 2
IADPSG: fasting 92, 1-hour 180, 2-hour 153 mg/dL. A single abnormal value diagnoses GDM The exam contrast in one line: one step, 75 g, one abnormal value; two step, 50 g screen then 100 g test, two abnormal values. One-step screening identifies more cases than two-step, without a demonstrated improvement in health outcomes — a direction the Task Force states, and percentages it leaves to its evidence report
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Screening timing USPSTF, 10 August 2021 (primary); ADA 2026 Section 15
Screen at 24 weeks of gestation or after — Grade B. Before 24 weeks the Task Force issued an I statement: evidence is insufficient to assess the balance of benefits and harms An I statement is not a recommendation against early screening in a high-risk patient — but it is also not a recommendation for it. ADA 2026 describes 24–28 weeks as the usual window for diagnosing and treating GDM, and says a benefit from treating everyone before then has not been shown
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Home self-monitored blood glucose ADA 2026, Recommendation 15.8 (grade B)
Fasting under 95 mg/dL, and either 1-hour postprandial under 140 or 2-hour postprandial under 120 mg/dL These are the numbers that decide diet control versus medication. ADA writes under 140 at one hour — use ADA's operators. Self-monitoring is the first element of treatment, not surveillance of it
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Hemoglobin A1C ADA 2026, Recommendation 15.9
A1C above 5.7% is a risk factor for GDM, not a diagnostic test for it. In pregnancy generally, ADA 2026 sets an ideal A1C goal of below 6% (42 mmol/mol) when that is reachable without significant hypoglycemia, relaxed to below 7% (53 mmol/mol) where needed to prevent hypoglycemia ADA 2026 notes that A1C runs slightly lower in pregnancy, with or without diabetes, because red blood cells turn over faster. NIDDK states that the A1C test should not be used to diagnose gestational diabetes — do not import the nonpregnant threshold
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Ultrasound estimated fetal weight StatPearls
Raises suspicion of macrosomia — but sensitivity is only 33% to 44% for birth weights above 4,500 g Macrosomia is "typically defined by an absolute birth weight," so it is confirmed at birth; before delivery, ultrasound "has limited accuracy, with errors increasing as fetal weight rises," and clinical methods are "similarly unreliable" — teach the limitation with the test, never the number alone
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Newborn blood glucose screening Pediatric Endocrine Society, as reported by StatPearls
Screened by protocol, not by symptoms. Target above 50 mg/dL in the first 48 hours of life and above 60 mg/dL thereafter, for at-risk infants without a suspected congenital disorder The screening list includes the infant of a diabetic mother, large for gestational age, premature or post-term delivery, perinatal stress and maternal preeclampsia. There is no universally accepted definition of neonatal hypoglycemia and recommendations on the intervention threshold vary — state the number with its owner and follow the unit protocol. On timing, British (BAPM), European (EFCNI) and Australian guidelines offer the first feed within the first hour and screen asymptomatic at-risk newborns just before the second feed (in practice no later than 2 to 4 hours after birth), then before feeds, with feeds every 2 to 3 hours (as summarised in a 2023 review of guidelines)
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Postpartum reclassification ADA 2026, Recommendations 15.30 and 15.31 (both grade B)
Glucose monitoring 24 to 72 hours after delivery, then a formal 75 g 2-hour OGTT at 4 to 12 weeks postpartum using nonpregnancy criteria Then lifelong screening every 1 to 3 years for type 2 diabetes or prediabetes. This appointment is the single most skipped and most consequential one on the page — after GDM "you will be at higher risk of developing type 2 diabetes later" (MedlinePlus).
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Placenta Previa & Abruption Antepartum hemorrhage
Digital cervical examination StatPearls, Placenta Previa
Do not perform one. Quoted: in suspected previa, "a digital examination should be avoided to prevent massive hemorrhage" The single most testable nursing fact on this page. No digital exam and no probing of the cervix in any patient bleeding after 20 weeks until the placenta has been located by ultrasound. The rule is written as an absolute, not a caution
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Transvaginal ultrasound StatPearls, Placenta Previa
Locates the placenta relative to the internal os. "Transvaginal sonogram has been shown to be superior to a transabdominal sonogram and is safe" The apparent contradiction is worth teaching explicitly: a probe, placed under ultrasound guidance in the vagina and not advanced into the cervix, is safe; a finger advanced into the cervical canal is not. Safe imaging does not license examination
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Follow-up ultrasound for a low-lying placenta StatPearls, Placenta Previa
Repeat at 28 to 32 weeks to look for persistent previa. About 90% of low-lying placentas resolve by the third trimester Resolution is not movement: the placenta "grows toward the increased blood supply at the fundus" while the lower segment lengthens beneath it. The earlier previa is diagnosed, the more likely it resolves by delivery
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Ultrasound for suspected abruption StatPearls, Placental Abruption
Cannot confirm or exclude the diagnosis. Sensitivity is low because "during the acute phase of placental abruption, the hemorrhage is isoechoic or similar to the surrounding placental tissue" Quoted: "the diagnosis of placental abruption cannot be confirmed or discarded based solely on an ultrasound," and "a definitive diagnosis… can only be made after birth, when the placenta is examined." A negative scan changes nothing about the clinical decision — treat the picture
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Continuous fetal heart-rate monitoring StatPearls, Placental Abruption
"An essential component of the evaluation." A Category III tracing indicates "high likelihood of fetal acidemia, suggesting that delivery is indicated" This is a diagnostic instrument, not a vigil. It is the earliest thing on the unit that will change, because the fetus loses exchange surface before the mother loses enough volume to move her vitals
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Fetal heart-rate categories — what each means in abruption StatPearls, Placental Abruption and Fetal Heart Rate Tracing
Category 1: reassuring — as NICHD-based studies classify it, baseline 110–160 bpm, moderate variability (6–25 bpm) and no recurrent decelerations; fetal acidemia unlikely, but it does not rule out abruption. Category 2: indeterminate — any tracing that fits neither category 1 nor category 3; may require additional evaluation. Category 3: "a high likelihood of fetal acidemia, suggesting that delivery is indicated if the category 3 tracing does not resolve with resuscitative measures." It is a sinusoidal pattern, or absent baseline variability with recurrent late decelerations, recurrent variable decelerations or bradycardia Deceleration meanings: late — they "reflect transient or chronic uteroplacental insufficiency," and interventions are indicated when true placental insufficiency is present; variable — cord compression; early — "considered benign." Category 2 is not a holding pattern: absent moderate variability or accelerations with significant decelerations in 50% or more of contractions for 30 minutes warrants cesarean or operative vaginal delivery
Normal Moderate variability or accelerations are a reassuring sign of normal acid/base status
Laboratory panel in suspected abruption StatPearls, Placental Abruption
Type and screen, complete blood count, and clotting studies — fibrinogen, prothrombin time, partial thromboplastin time — plus blood urea nitrogen and a Kleihauer-Betke test Fibrinogen is the number to watch, because it is being consumed inside the uterus. The DIC page owns the caveat that fibrinogen can be normal or even high early in DIC while consumption is already underway — one normal value is not clearance
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Kleihauer-Betke test StatPearls, Kleihauer-Betke Test
An acid-elution assay on maternal blood quantifying fetal hemoglobin that has entered the maternal circulation. Any value other than zero is abnormal and suggests fetomaternal hemorrhage Two limits change practice. False positives occur in conditions associated with elevated maternal fetal hemoglobin. And sensitivity is low, with "a positivity threshold of approximately 5 mL" while as little as 0.01 to 0.03 mL can cause isoimmunization. A negative result therefore never cancels the routine Rh immune globulin dose; it only fails to justify extra vials
Normal Dose arithmetic: one vial is 300 mcg and covers 30 mL of fetal blood; volume in mL = percent fetal cells x 50; vials = volume divided by 30, rounding decimals of 5 or more up and under 5 down, then add one vial
Imaging for placenta accreta spectrum StatPearls, Placenta Accreta
Ultrasound sensitivity 90.8%, specificity 96.9%. Findings: loss of the hypoechoic retroplacental space, lacunae with turbulent Doppler flow, myometrial thinning The presence of previa raises diagnostic accuracy "from 6.9% to 72.3%," which is another way of saying that previa plus prior cesareans is the setup you go looking for accreta in
Normal MRI sensitivity 94.4%, specificity 84.0% — reserved for inconclusive ultrasound
Preterm Labor PTL
Fetal fibronectin StatPearls, Preterm Labor
Best used for its negative result. "The primary utility… is its negative predictive value; the absence of fFN is associated with a low risk of birth within 7 days." Positive is 50 ng/mL or above, which raises risk, "though the positive predictive value of this test is still relatively low," alone — though with an intermediate cervical length it does rule in high risk of birth within 7 days Collection sequence is the test's validity: obtain it before any digital cervical exam, before blood exposure and away from recent intercourse, each of which "can all lead to false-positive results." Swab first, examine second. A positive result does not commit anyone to delivery; a negative one buys real reassurance
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Transvaginal cervical length StatPearls, Preterm Labor; cerclage threshold from StatPearls, Cervical Cerclage
Normal 35 to 48 mm, with a preterm birth risk under 5% at 30 mm or more. Risk is stratified with fibronectin rather than by length alone: under 15 to 20 mm is high risk for birth within 7 days regardless of the fibronectin result, and an intermediate length of 15 to 20 mm up to 30 mm with a positive fibronectin is also high risk The same number drives an intervention: ultrasound-indicated cerclage is considered with a prior spontaneous loss or preterm birth before 34 weeks plus a cervical length under 25 mm before 24 weeks in a singleton pregnancy
Normal Most predictive before 34 weeks
Diagnosis of ruptured membranes StatPearls, Preterm and Term Prelabor Rupture of Membranes
Sterile speculum examination first. "Direct visualization of fluid leakage from the cervical os or gross pooling confirms the diagnosis" — pooling being "the rapid collection of amniotic fluid in the lower blade of the speculum" No digital examination. Quoted: digital exams "increase the risk of intraamniotic infection in patients with ROM; digital examinations… should be avoided unless delivery appears imminent or the patient appears to be in active labor."
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Ferning and nitrazine StatPearls, Preterm and Term Prelabor Rupture of Membranes
Ferning: dried amniotic fluid "forms a crystalized pattern that appears like branches of a fern tree." Nitrazine: amniotic fluid pH is 7 to 7.4, against normal pregnancy vaginal secretions of 3.8 to 4 Both have specific confounders. Cervical mucus also ferns, but "in thick linear bands secondary to its stringlike macroscopic structure." And "false-positive pH tests… are common, as multiple other causes of abnormally high vaginal pH may be present." Neither test is used alone to overturn a clinical picture
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Commercial amniotic protein assays StatPearls, Preterm and Term Prelabor Rupture of Membranes
Detect placental alpha microglobulin-1 or insulin-like growth factor binding protein-1. Sensitivity about 95% to 99% These outperform ferning and nitrazine, which is worth knowing when a conventional test is negative in a patient who is convincingly leaking fluid. Ultrasound is also recommended to assess amniotic fluid volume, since oligohydramnios is often seen
Normal Conventional bedside methods run at about 85%
White blood cell count and inflammatory markers StatPearls, Preterm and Term Prelabor Rupture of Membranes
Not an infection test in this setting. "In the absence of clinical findings suggesting intraamniotic infection… an elevated white blood count is nonspecific," and antenatal steroids raise it independently Antenatal corticosteroids also raise the white count, so a rise after a betamethasone dose is expected rather than alarming. The diagnosis of intraamniotic infection is made from fever, fetal tachycardia, uterine tenderness and discharge
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Group B streptococcus rectovaginal culture StatPearls, Streptococcus Group B (screening window and indications)
Routine screening culture between 36 0/7 and 37 6/7 weeks of gestation; a positive culture is an indication for intrapartum antibiotic prophylaxis The collision with this page is the point: a patient in preterm labor at 30 weeks has not reached the screening window. That is exactly why unknown status plus preterm delivery before 37 weeks is itself an indication for prophylaxis. Penicillin-allergy regimens belong to the prescriber and the class page, but the specimen matters: the GBS sample should state the penicillin allergy, and for a patient at high risk of anaphylaxis to penicillin it should request clindamycin susceptibility testing, because 20% to 30% of GBS isolates are clindamycin resistant.
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Continuous fetal heart-rate monitoring NICHD three-tier system — the placenta-previa-abruption page cites the monitoring chapter and owns this table
Continuous cardiotocography monitors fetal well-being and contraction patterns during preterm labor; moderate variability or accelerations are reassuring In ruptured membranes fetal well-being "is typically accomplished with cardiotocographic monitoring and a biophysical profile." Fetal tachycardia (above 160 beats/min, one of the clinical chorioamnionitis criteria alongside maternal fever) is read here as an infection sign, not only a tracing finding. The category meanings, the variability bands and the deceleration meanings are owned by the placenta-previa-abruption page — follow the link rather than learning them twice
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Assessment for intraamniotic infection StatPearls, Preterm and Term Prelabor Rupture of Membranes
The sourced sign set is fever, an elevated white cell count, uterine tenderness, abdominal pain, foul-smelling vaginal discharge, and fetal and maternal tachycardia This is a clinical assessment run on a schedule, not a laboratory diagnosis. A rise in maternal temperature is the instrument that starts it, and the white cell count explicitly does not: it is "nonspecific" absent clinical findings, and antenatal steroids raise it independently. A separate chorioamnionitis literature adds a two-tier fever rule and a named antibiotic regimen; neither is carried here, because this page does not cite that chapter
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Ectopic Pregnancy Tubal pregnancy
Serum and urine beta-hCG StatPearls, Human Chorionic Gonadotropin
Serum assays detect "as low as 1 to 2 mIU/mL." Urine tests turn positive "typically starting at 20 to 50 mIU/mL… corresponding to levels approximately 4 weeks post-conception" False positives arise from ectopic hCG production by malignancies, "Heterophile antibodies," "Rheumatoid factors," and blood in the urine, which "may cause a false-positive result." False negatives arise from testing too early, dilute urine, and the hook effect at approximately 500,000 mIU/mL. The test answers whether, never where
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Serial hCG at 48 hours Women's Health 2023 review (49% and 21% rules); StatPearls, Human Chorionic Gonadotropin (24-hour doubling)
"Viable IUPs are 99% likely to have a 49% increase in β-hCG levels over 48 h when initial levels were < 1500 mIU/mL." "Decreasing levels or a slower rate is suggestive of miscarriage or EP, with a decrease of 21% or greater most likely a failed IUP" "hCG doubles every 48 hours" is a blend of those two rules and is stated by neither source. Teach the 49%-over-48-hours figure, because it is the one attached to the diagnostic decision, and note that its condition is a starting level under 1,500
Normal A separate source describes the overall first-trimester trajectory as "doubling approximately every 24 hours for the first 8 weeks"
The discriminatory zone StatPearls, Ectopic Pregnancy, Ultrasound; F&S Reports 2021 (3,500 zone); Women's Health 2023 review (2,000 figure)
The hCG level at which an intrauterine sac should be visible on transvaginal ultrasound in a normal pregnancy. Recent data suggested "broadening the discriminatory zone for hCG level from 1,500 to 3,500 mIU/mL" The threshold was raised deliberately, and the direction is the teaching point: a lower cutoff risks ending a viable intrauterine pregnancy that is simply too early to see. A level above 2,000 with no visible intrauterine pregnancy is "highly suspicious of EP," which is suspicious rather than diagnostic
Normal Older teaching used a lower cutoff: the ultrasound chapter says 1,500 to 2,000 mIU/mL "has been accepted in the past" — do not act on a historical figure
Transvaginal ultrasound StatPearls, Ectopic Pregnancy and Ectopic Pregnancy, Ultrasound; Women's Health 2023 review (tubal findings)
"TVUS has been demonstrated to be the most sensitive and accurate for early detection of ectopic pregnancy." The tubal picture is an "Extraovarian mass containing yolk sac and/or fetal pole," with or without cardiac motion The pseudogestational-sac trap, quoted: "caution should be taken when identifying fluid surrounding the suspected pregnancy. If this is the focus of the examination instead of the endometrial stripe, an ectopic pregnancy may be mistaken as an intrauterine pregnancy." In an unstable patient, bedside imaging comes first and is "especially important in a hemodynamically unstable patient"
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Ultrasound findings and their performance StatPearls, Ectopic Pregnancy, Ultrasound
Tubal ring sign — an echogenic ring around a likely unruptured ectopic — has a 95% positive predictive value. A complex extra-adnexal cyst or mass with no intrauterine pregnancy has a 95% chance of being a tubal ectopic 63% sensitivity is why a negative scan rules nothing out. Site-specific criteria exist too: the interstitial line sign with a myometrial mantle under 5 mm thick for interstitial pregnancy, and the Spiegelberg criteria for ovarian pregnancy
Normal Free pelvic fluid or hemoperitoneum in the pouch of Douglas with a positive hCG is 70% specific and 63% sensitive
Pregnancy of unknown location Women's Health 2023 review; StatPearls, Ectopic Pregnancy, Ultrasound
A named working diagnosis when a pregnancy test is positive and no pregnancy is visible. Of these patients, "50%–70% are found to have either an EP or miscarriage, while the remaining 30% may have a normal IUP," and "Serial β-hCG levels are monitored to determine pregnancy location and prognosis" This is a diagnosis with a follow-up plan attached, not a negative result. An unlocated pregnancy is followed, never discharged without one. An identified intrauterine pregnancy "greatly decreases the chances of an ectopic pregnancy being present" — with heterotopic pregnancy after assisted reproduction as the exception
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hCG as a treatment threshold StatPearls, Ectopic Pregnancy; Women's Health 2023 review; NHS
Above 5,000 mIU/mL is a relative contraindication to methotrexate, alongside fetal cardiac activity and an adnexal mass over 4 cm, and "Surgical management is indicated in patients exhibiting MTX contraindications" Methotrexate "efficacy decreases as initial β-hCG levels increase," which is why the number sorts patients. Expectant management is considered for patients without symptoms whose level is low and falling with no gestational sac seen: spontaneous resolution is reported in 88% when the initial β-hCG is below 200 mIU/mL, and monitoring continues until the level falls below 15 IU/L (numerically the same as 15 mIU/mL; as summarised in a 2025 methotrexate study). In a randomized trial of women with β-hCG below 2,000 mIU/mL, expectant management succeeded in 59% versus 76% with methotrexate, a difference that was not statistically significant
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Methotrexate surveillance StatPearls, Ectopic Pregnancy
Serum hCG on day 4 and day 7 after administration. A decline of at least 15% between days 4 and 7 indicates effective treatment. Then weekly monitoring until undetectable, up to 8 weeks These two draws are the treatment, not the paperwork. "Unreliable follow-up" is an absolute contraindication to methotrexate — a patient who cannot return on day 4 and day 7 is not a candidate, however good her laboratory values are
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Blood type and antibody screen StatPearls, Rho(D) Immune Globulin
Establishes Rh status. Ectopic pregnancy is an explicitly named indication for Rho(D) immune globulin in an Rh-negative, non-sensitized patient The indication list also covers threatened abortion, second- and third-trimester fetal demise, spontaneous or induced abortion, and invasive obstetric procedures. Vial conversion: 1 microgram equals 5 international units, so a 300 mcg vial is 1,500 IU
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STIs & PID PID
Chlamydia and gonorrhea screening US Preventive Services Task Force, 14 September 2021
Grade B — screen sexually active women 24 years or younger, and those 25 or older at increased risk, for chlamydia and for gonorrhea. The recommendation explicitly includes pregnant persons No fixed interval is set. "A reasonable approach would be to screen patients whose sexual history reveals new or persistent risk factors since the last negative test result." The CDC line matches: annual screening of all sexually active women under 25
Normal For men the Task Force issues a Grade I statement: "the current evidence is insufficient to assess the balance of benefits and harms"
PID minimum criteria CDC STI Treatment Guidelines, 2021
Cervical motion tenderness, uterine tenderness, OR adnexal tenderness on pelvic examination, in a sexually active woman with pelvic or lower abdominal pain The "or" is the exam item — one of the three suffices. The bar is deliberately low so PID is treated presumptively, because the cost of waiting for confirmation is tubal damage. A pregnancy test is run alongside, because cervical motion tenderness is shared with ectopic pregnancy
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PID supportive and specific criteria CDC STI Treatment Guidelines, 2021
Supportive: oral temperature above 38.3 °C (101 °F), mucopurulent cervical discharge or cervical friability, abundant white cells on saline microscopy, elevated ESR, elevated CRP, documented cervical gonorrhea or chlamydia Two fever numbers must not be merged: 38.3 °C is the supportive criterion; 38.5 °C is the hospitalization criterion. A widely circulated version of the supportive criterion prints 38.5 °C, which is a transcription divergence from the guideline itself
Normal Most specific: endometrial biopsy showing endometritis; imaging showing thickened, fluid-filled tubes; laparoscopic findings consistent with PID
Nontreponemal titers for monitoring CDC STI Treatment Guidelines, 2021 — primary and secondary, and latent syphilis sections
Nontreponemal titers are what treatment is judged by, and the threshold that matters is a fourfold change — treatment failure or reinfection is defined as "at least a fourfold increase in nontreponemal test titer persisting for >2 weeks," or failure of titers to decrease fourfold within 12 months Treponemal tests stay positive for life and cannot be used to judge response, which is why the follow-up schedule is built on the nontreponemal titer: 6 and 12 months after treatment for primary and secondary syphilis, and 6, 12 and 24 months for latent syphilis
Normal Follow-up schedule: primary and secondary at 6 and 12 months; latent at 6, 12 and 24 months
Maternal syphilis screening in pregnancy StatPearls, Congenital and Maternal Syphilis
Screen "at the first prenatal visit, at about 28 weeks of gestation, and again at delivery, particularly for higher-risk mothers" The reason for the repeats is stated: "many women can be infected with syphilis during pregnancy." This is the cue that matters, because 70% of infants born with congenital syphilis are asymptomatic at birth and the baby's appearance is not a screening tool
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Retesting after treatment CDC STI Treatment Guidelines, 2021
Chlamydia and genital gonorrhea: retest at approximately 3 months after treatment, "regardless of whether they believe their sex partners were treated." The scoping of that wording is the teaching: the retest is done whatever the partner situation, which tells you what it is for Explain to patients that the 3-month retest exists because reinfection is common, not because the treatment is doubted
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Doxy-PEP monitoring CDC Clinical Guidelines on Doxycycline Postexposure Prophylaxis, 2024 (MMWR Recomm Rep)
Persons prescribed doxycycline post-exposure prophylaxis require "bacterial STI testing at anatomic sites of exposure at baseline and every 3–6 months thereafter," with ongoing need reassessed every 3 to 6 months The eligibility criterion doubles as a risk-factor statement: counselling is directed at gay, bisexual and other men who have sex with men and transgender women with a history of at least one bacterial STI "(specifically, syphilis, chlamydia or gonorrhea) during the past 12 months"
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Breast Cancer Invasive ductal carcinoma
Screening mammography USPSTF 2024
Masses, calcifications or architectural distortion Biennial, ages 40 to 74 (Grade B). Evidence is insufficient for 75 and older and for supplemental ultrasound or MRI in dense breasts; mammography "is of limited utility in patients with dense breasts, in younger patients"
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Image-guided core needle biopsy
Tissue diagnosis — ductal, lobular, DCIS "Core needle biopsy is superior to fine needle aspiration and should be performed whenever possible"; a marker is placed at the site
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Estrogen receptor, progesterone receptor, HER2
Defines the subtype — luminal A, luminal B, HER2-enriched, triple-negative "All specimens should be tested"; genomic risk testing guides chemotherapy in hormone receptor–positive disease
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Breast MRI
"the most sensitive imaging study" But "time-consuming, has limited availability, and is expensive"
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Staging imaging
CT chest/abdomen/pelvis with bone scan or FDG-PET in advanced disease "Routine laboratory investigations and imaging for systemic disease are not recommended for operable breast cancer in the absence of symptoms"
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Baseline and serial cardiac function (with trastuzumab) FDA label
LVEF before and during anti-HER2 therapy "Evaluate cardiac function prior to and during treatment. Discontinue Herceptin for cardiomyopathy"
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PMOS (PCOS) & Endometriosis PMOS
PMOS diagnosis — 2 of 3 criteria 2023 International PCOS Guideline (via StatPearls)
Clinical or biochemical hyperandrogenism, ovulatory dysfunction, and polycystic ovaries on ultrasound or raised AMH — plus exclusion of mimics. Adolescents need both hyperandrogenism and ovulatory dysfunction; ultrasound and AMH are not recommended in adolescents. The NHS does an ultrasound only if over 18.
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Tests to exclude PMOS mimics
Androgen levels, plus tests for the mimics — thyroid disease, hyperprolactinemia and atypical congenital adrenal hyperplasia. Testosterone, FSH, LH and AMH are unreliable on the pill — check after being off it for at least 3 months.
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Metabolic screen at PMOS diagnosis
BMI and waist circumference, blood pressure, diabetes screening, lipids; ask about sleep-apnea symptoms. Follow-up frequency depends on results. More than half develop diabetes or prediabetes before their early 40s.
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Endometriosis work-up
Pelvic examination, blood tests, ultrasound (abdominal or transvaginal), MRI; laparoscopy confirms. "Histopathologic evaluation remains the gold standard." Exclude ectopic or early pregnancy first.
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Prostate & Testicular Cancer Prostate cancer
PSA (prostate-specific antigen)
Raised in cancer — and in BPH, prostatitis, infection, after DRE, ejaculation or instrumentation. 4.0 ng/mL or more is "the consensus standard for further prostate cancer evaluation". 5-ARIs halve PSA after 6–12 months — the value is doubled for screening.
Normal No level reliably rules cancer in or out
Prostate biopsy — Gleason score
6 low grade · 7 medium · 8–10 high grade. Watch for fever, pain, blood in urine or semen, and UTI afterwards.
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Scrotal ultrasound
Solid intratesticular mass in testicular cancer. With examination, "nearly 100% sensitivity"; routine ultrasound is not done in men with no palpable mass.
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Testicular tumor markers — AFP, hCG, LDH
Drawn before orchiectomy; used for staging and to follow treatment and relapse. AFP is never raised in pure seminoma; about 15% of seminomas express hCG.
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Blood glucose and lipids on ADT
Hyperglycemia, hyperlipidemia; QT prolongation possible. GnRH agonists carry metabolic and cardiovascular warnings.
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Postpartum Depression & Postpartum Psychosis PPD
Edinburgh Postnatal Depression Scale (EPDS) StatPearls
Score ≥13 = increased risk (StatPearls); many institutions refer above 9–10 "the most frequently used is the EPDS, a 10-item questionnaire completed by patients within a few minutes." "The highest score possible is 30." Referral thresholds vary; suicidal ideation prompts referral regardless of score. PHQ-9 and GAD-7 are alternatives.
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Nurse screening per agency policy
Screen postpartum mothers; teach blues vs PPD Open RN: "The nurse administers a postpartum depression screening tool to postpartum mothers based on agency policy, such as the Edinburgh Postnatal Depression Scale (EPDS)." USPSTF: "The USPSTF recommends screening for depression in adults, including pregnant and postpartum women."
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Clinical evaluation
Major depressive episode with peripartum onset; suicidal/homicidal risk assessed "The objectives of the clinical evaluation are to constitute the diagnosis, assess suicidal and homicidal risks, and rule out other psychiatric illnesses." Consider bipolar disorder if symptoms last more than 2 weeks with prominent irritability.
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Thyroid-stimulating hormone (TSH)
Normal — rules out thyroid cause "Thyroid disorders can be assessed by testing thyroid-stimulating hormone levels."
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[PSY] EPDS + Mood Disorder Questionnaire (MDQ)
Identify depression and mania in at-risk mothers "EPDS (Edinburgh postnatal depression scale) and MDQ (mood disorder questionnaire) are quick and effective screening tools to identify signs of depression and mania in populations at risk."
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[PSY] Organic work-up: CBC, electrolytes, glucose, thyroid tests, urine drug screen, brain CT/MRI
No medical cause of psychosis Done "to rule out medical conditions and organic causes that may present as psychosis" — e.g., stroke "especially in women with a history of pregnancy-induced hypertension, preeclampsia, and eclampsia."
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Hyperemesis Gravidarum HG
Weight and fluid status
Weight loss vs prepregnancy; low BP, high HR, dry mucous membranes, poor turgor Exam includes "blood pressure, heart rate, mucous membrane dryness, capillary refill, and skin turgor. A patient's weight should be obtained for comparison to previous and future weights." Fetal heart rate "when at a detectable gestational age."
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Urine ketones
Positive "The presence of ketonuria may guide decisions regarding the need for intravenous fluids, nutritional support, or hospitalization."
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Electrolytes, BUN, creatinine
Hypokalemia, hyponatremia, elevated BUN/creatinine Dehydration and electrolyte loss from "prolonged vomiting and reduced nutritional intake." Vomiting pattern: metabolic alkalosis (StatPearls physiology).
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Hemoglobin/hematocrit; liver enzymes
Raised Hgb/Hct from hemoconcentration; liver enzymes may be elevated "Liver enzyme elevations are observed in up to half of hyperemesis gravidarum cases."
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Thyroid tests (TSH, free T4)
May show suppressed TSH, elevated free T4 Transient gestational thyrotoxicosis is "usually benign, self-limited" and managed "with supportive care rather than pharmacological intervention" — no antithyroid drugs.
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Obstetric ultrasound
Rule out molar pregnancy and multiples "The workup may begin with an obstetric ultrasound scan, which will confirm the diagnosis in most cases." "Imaging is not essential for diagnosing hyperemesis gravidarum, but can be instrumental in ruling out other conditions."
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ECG (if on ondansetron with electrolyte abnormality) FDA label (ondansetron)
No QT prolongation Ondansetron label: "Avoid in patients with congenital long QT syndrome; monitor with electrocardiograms (ECGs) if concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or use of other QT prolonging drugs."
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Cervical & Ovarian Cancer Cervical carcinoma
[SCR-C] Cervical screening, ages 21–29 USPSTF 2018
Cytology (Pap) alone every 3 years Grade A. Cytology only before 30 because of "the high prevalence of transient HPV infection among adolescents and young adults." No screening before 21 (Grade D) — even if sexually active.
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[SCR-C] Cervical screening, ages 30–65 USPSTF 2018
Cytology every 3 years, OR high-risk HPV test alone every 5 years, OR cotesting every 5 years Grade A. Stop after 65 with adequate prior screening and no high risk, and after hysterectomy with the cervix removed and no history of CIN 2/3 or cancer (Grade D) — "clinicians should confirm through review of surgical records or direct examination that the cervix was removed." Does not apply to women with high-grade lesions, cancer, in-utero DES or a compromised immune system (e.g., HIV).
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[SCR-C24] 2024 USPSTF DRAFT (not final) USPSTF 2024 draft
HPV primary screening every 5 years from 30 as the preferred strategy — clinician- or patient-collected Draft dated December 10, 2024: "When finalized, this recommendation will update the 2018 USPSTF recommendation." Until finalized, the 2018 statement stands.
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[CERV] Colposcopy and biopsy
Confirms precancer or cancer after abnormal cytology or persistent high-risk HPV "Colposcopy is the diagnostic procedure of choice"; "A diagnostic biopsy is needed to finalize the diagnosis." Precancer: cryotherapy or excision; conization, laser or LEEP for larger lesions. Conization complications: "hemorrhage, infection, cervical incompetence, cervical stenosis, and infertility."
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[SCR-O] Ovarian screening in average-risk women USPSTF 2018
Not recommended — CA-125, transvaginal ultrasound or both do not reduce deaths Grade D for asymptomatic women "not known to have a high-risk hereditary cancer syndrome." Screening harms include "many false-positive results, which can lead to unnecessary surgical interventions."
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[OVAR] Ultrasound, CT or PET (symptoms or mass)
Images the pelvis and abdomen NCI lists an ultrasound exam (some patients have a transvaginal ultrasound), CT scan and PET scan among the tests used "to diagnose and stage" these cancers, with a pelvic exam and CA-125.
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[OVAR] CA-125
Raised in most advanced cases; raised in only about half of early cases Not diagnostic. "CA-125 levels are increased in most advanced epithelial ovarian cancer cases but are elevated only in 50% of early-stage disease cases; therefore, the sensitivity of this biomarker is limited." "An increased CA-125 level can be a sign of cancer or another condition such as endometriosis." Tissue for diagnosis "is usually removed during surgery to remove the tumor."
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Spontaneous Abortion Miscarriage
Vital signs and bleeding estimate
Stable vs tachycardia or hypotension StatPearls: a focused exam with vital signs "will assist in determining if hemodynamic instability and/or possible ectopic pregnancy need to be emergently addressed." Document the bleeding history — "the number of soaked pads in an hour, and the number and size of clots."
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Pelvic exam
Open or closed os; tissue in the os; signs of infection StatPearls: findings "may include an open or closed cervix, the presence or absence of pregnancy tissue within the cervical os, vaginal bleeding, and signs suggestive of a septic abortion (eg, purulent discharge, uterine or cervical motion tenderness)."
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Transvaginal ultrasound + serial β-hCG
Location and viability of the pregnancy StatPearls: "Trending β-hCG levels with the findings from pelvic ultrasound assist in assessing the viability of the pregnancy." If no pregnancy is seen, "the immediate step is to determine the gestational age and location of the fertilized egg to exclude an ectopic pregnancy."
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Blood type, Rh and antibody status FDA labels (RhoGAM, HyperRHO Mini-Dose)
Rh(D)-negative and unsensitized → candidate for anti-D HyperRHO Mini-Dose label: "The mother must be Rh o (D) negative and must not already be sensitized to the Rh o (D) antigen."
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CBC; type and crossmatch if bleeding heavily
Anemia = blood loss; leukocytosis = infection; low platelets = possible DIC StatPearls (Abortion Complications): "Leukocytosis suggests an infection, whereas anemia may indicate significant blood loss. Thrombocytopenia is a common feature of disseminated intravascular coagulation." "In the case of hemorrhage that could require transfusion, the patient's blood should be typed, screened, and cross-matched."
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Cultures (if infection is suspected)
Cervix, urine, endometrium StatPearls (Abortion Complications): "If infection is suspected, cultures of the cervix, urine, and endometrium should be obtained."
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Rh(D) Alloimmunization Rh incompatibility
ABO/Rh type + antibody screen (indirect Coombs) — mother
Rh-negative; anti-D absent (unsensitized) or present (sensitized) StatPearls: "All pregnant women undergo an ABO blood group and Rh-D type and antibody screening assessment at the first prenatal visit with each pregnancy." NCBI: "The indirect Coombs test finds anti-D antibodies in the mother's serum." "Clinicians should repeat an antibody screen in Rh-negative women before anti-D immune globulin administration" (StatPearls).
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Antibody screen after Rh(D) immune globulin FDA label (RhoGAM)
May be positive from passively given anti-D RhoGAM label: "The presence of passively acquired anti-D antibodies in the maternal serum may cause a positive antibody screening test. This does not preclude further antepartum or postpartum prophylaxis."
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Rosette screen → Kleihauer-Betke test (maternal blood)
Rosette positive → KB quantifies the fetal bleed StatPearls: "If the rosette test is positive, a Kleihauer-Betke test should be performed to confirm the presence of fetomaternal hemorrhage and quantify its volume." "In cases of major trauma, the Kleihauer-Betke test may be used directly without prior screening." It "guides appropriate dosing of Rho(D) immune globulin to prevent alloimmunization."
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Serial antibody titers (sensitized mother)
Rising titer suggests active hemolysis NCBI: "Monitoring includes regular ultrasound scans of the fetus and monitoring of the amount of anti-D in the mother's serum. Active hemolysis is indicated by a rise in anti-D."
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Fetal MCA Doppler
Peak systolic velocity > 1.5 MoM = fetal anemia StatPearls: "Typically, serial MCA Doppler assessment is performed every 1 to 2 weeks from 24 weeks gestation." PSV > 1.5 MoM "is typically an indication for cordocentesis"; "An intrauterine transfusion is considered when the fetal hemoglobin is <2 standard deviations below the mean for gestational age or the hematocrit is <30%."
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Direct antiglobulin test (direct Coombs) — newborn
Positive = maternal antibody on the baby's red cells NCBI: "The direct Coombs test detects maternal anti-D antibodies that have already bound to fetal RBCs." StatPearls: "a positive DAT is diagnostic of HDFN."
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Newborn bilirubin and hemoglobin
Rapidly rising bilirubin; anemia NCBI: "Within 24 hours of birth, the level of bilirubin may rise dramatically"; a sharp rise "can be lowered by phototherapy and exchange transfusions."
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Newborn jaundice checks — TcB screen, TSB confirmation CDC (archived page, 2020)
Measure bilirubin — do not rely on skin color alone CDC (archived, 2020): "At a minimum, babies should be checked for jaundice every 8 to 12 hours in the first 48 hours of life." A transcutaneous meter is "placed on the baby’s head," and if the TcB is high a blood test follows; "The best way to accurately measure bilirubin is with a small blood sample from the baby’s heel." In darker skin, "Checking the gums and inner lips may detect jaundice. If there is any doubt, a bilirubin test should be done."
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Postpartum Infection Puerperal infection
Temperature pattern
≥ 38.0 °C (100.4 °F) on any 2 of the first 10 days, excluding the first 24 hours StatPearls definition of postpartum fever. Other causes of postpartum fever include "deep vein thrombosis and breast engorgement," and postpartum patients "may also develop infections unrelated to their puerperal status."
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Blood and wound cultures
Identify the organism; narrow therapy StatPearls: "evaluation should include blood and wound cultures before initiating antibiotics, if time permits." In sepsis, "blood cultures should be obtained before antibiotic administration if doing so does not significantly delay antibiotics."
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CBC with differential
Leukocytosis 15,000–30,000/μL, bandemia > 10% suggest infection StatPearls (Endometritis): "Leukocytosis is a normal finding immediately postpartum, especially in those who underwent cesarean delivery." StatPearls: "no postpartum infection can be ruled out based solely on laboratory work, and clinicians should not be falsely reassured if laboratory diagnostics are unremarkable."
Normal Leukocytosis is normal immediately postpartum
Sepsis labs — lactate, metabolic panel, coagulation panel
Lactic acidosis, organ dysfunction StatPearls (Endometritis): obtain them "if patients have findings suspicious for sepsis (eg, fever >102 °F [38.9 °C], tachycardia, tachypnea, or hypotension)."
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Urinalysis and urine culture
Rule out UTI StatPearls (Endometritis): "A urinalysis and culture should also be obtained to rule out urinary tract infections (UTIs), which can have similar symptomatology."
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Imaging
Pelvic ultrasound first; CT or MRI for deep infection or pelvic vein thrombosis StatPearls (Endometritis): "imaging is rarely helpful unless an alternative diagnosis (eg, retained products of conception or septic pelvic thrombophlebitis) is suspected." StatPearls: "If postsurgical deep organ infection is suspected, CT with intravenous contrast may help with diagnosis." For necrotizing fasciitis, "definitive diagnosis and management are surgical."
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Mastitis work-up
Clinical diagnosis; milk culture and breast ultrasound if not improving StatPearls, citing ABM: "Lactational mastitis is primarily diagnosed based on history and clinical findings." "A breast ultrasound can be obtained if an abscess is suspected." "A biopsy is not recommended to evaluate lactational mastitis."
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Sensory

Glaucoma
Intraocular pressure by tonometry Population reference range, as reported by StatPearls
Normal is 10 to 21 mm Hg. In acute angle closure it is "typically 50 to 80 mm Hg," and can "reach levels of 60–80 mm Hg" on examination. A pressure below the normal range — hypotony — suggests "uveitis, ocular traumas, retinal detachment, and post-surgery complications, especially after filtering surgery" Read 10 to 21 as a population reference, not as a diagnostic boundary. Normal-tension glaucoma "is open-angle with a presenting IOP in the normal range," and equally that a raised reading is not a diagnosis, since "IOP levels greater than 21 mm Hg do not necessarily cause glaucoma." Do not use 40 mm Hg as a diagnostic figure for an acute attack either; 40 is the separate threshold below which pilocarpine becomes useful.
Normal 10 to 21 mm Hg
The open-angle diagnostic triad StatPearls
Optic disc or retinal nerve fiber layer changes · visual field changes · elevated IOP — all three, not pressure alone. Two errors this triad prevents, and they point in opposite directions. A normal pressure does not exclude glaucoma — normal-tension glaucoma is open-angle disease with an IOP in the normal range, and "Once progression has been demonstrated, CNTGS showed an aggressive IOP lowering of 30%, leading to a slower visual field loss rate." And a high pressure is not a diagnosis — "IOP levels greater than 21 mm Hg do not necessarily cause glaucoma… studies have shown asymptomatic individuals with OCULAR HYPERTENSION who maintain normal visual fields and healthy optic nerves"
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Optic disc examination and the ISNT rule
Examine with a slit lamp and a 90D or 78D lens. The ISNT rule: the Inferior neuroretinal rim is thickest, then Superior, Nasal, Temporal. In open-angle glaucoma "the superior and inferior NRR are thinned, BREAKING the ISNT rule." Typical findings: notching or shelving of the rim superiorly or inferiorly · cup-to-disc ratio greater than 0.5 · increased VERTICAL cup-to-disc ratio · asymmetry of 0.2 or more between eyes · disc haemorrhage · peripapillary atrophy "The optic cup should be determined by its contour and not color." A systematic review found "the risk of glaucoma was highest when an examination revealed an increased cup-disk ratio (CDR), CDR asymmetry, disc hemorrhage, or elevated IOP" — note that three of those four are disc findings, not pressure
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Gonioscopy — including of the unaffected eye StatPearls
Distinguishes an open angle from a closed one, and in an acute attack shows 360-degree closure. "Gonioscopy of the unaffected eye may reveal a narrow, almost occluded angle" That second sentence is the basis of the fellow-eye rule. The untreated opposite eye "shares the same anatomic predisposing factors as the first eye" and "has a 40% to 80% chance of developing an AAC glaucoma within 5 to 10 years. Therefore, it is recommended to perform LPI in BOTH eyes to reduce the risk of such an attack."
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Visual field testing and optical coherence tomography
Automated static perimetry measures "the patient’s ability to perceive visual stimuli at different locations," and serial testing over time gives "valuable information about the condition’s progression and the treatment’s effectiveness." OCT assesses retinal nerve fibre layer thickness, with serial scans "Serial OCT scans enable monitoring of changes over time" These are the instruments that follow the disease rather than diagnose it. Anterior segment OCT and ultrasound biomicroscopy are used in patients with angle-closure risk factors. The complete examination also includes dilated fundoscopy, slit lamp, pupillary reflex response, visual acuity and visual field measurement — and dilation is itself the step that must be reconsidered in an eye with a narrow angle
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What is NOT needed in the acute attack
Imaging. "In the acute phase of AAC, imaging studies are generally unnecessary for diagnosis. The clinical signs and symptoms, along with findings from slit-lamp examination and IOP measurement, are usually sufficient" This is the direct counterweight to the commonest error on this page — the headache-plus-vomiting presentation that gets a CT scan and a neurology consult while the eye goes untreated. The differential the source names includes migraine and cluster headache alongside conjunctivitis, keratitis, scleritis, corneal ulcer, trauma and chemical injury
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Basic metabolic panel — one specific indication
"If osmotic agents, such as mannitol or glycerin, are used as part of the treatment regimen, a basic metabolic panel can help monitor electrolyte levels and renal function due to their potential systemic effects" The other monitoring requirement during an attack is the pressure itself: "it is advisable to measure IOP AT LEAST HOURLY after the initial onset of symptoms until it stabilizes"
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Screening — two answers to two different questions USPSTF 2022 (primary); AOA baseline exam as reported by the USPSTF; NEI
USPSTF, 24 May 2022 — an I statement: "the current evidence is insufficient to assess the balance of benefits and harms of screening for primary open-angle glaucoma in [asymptomatic] adults [40 years or older]." The American Optometric Association (with a second, excluded body; as reported by the USPSTF) recommends a baseline comprehensive eye evaluation at age 40, and NEI advises that "If you’re at higher risk, you need to get a comprehensive dilated eye exam every 1 to 2 years." An I statement is not a recommendation against screening. The Task Force’s own implementation wording is "insufficient evidence to recommend for or against… clinicians should use their clinical judgement." It applies to primary care and explicitly not to symptomatic adults or to angle-closure and secondary glaucoma. Its reasoning: screening tests "are not commonly administered in the primary care setting," progression "cannot be precisely predicted," and there is "limited evidence about whether or not these changes lead to improvements in visual impairment, vision-related function, and quality of life." The eye-examination advice comes from the AOA and NEI — not from the Task Force’s own recommendation
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Ménière’s Disease & Hearing Loss Meniere disease (endolymphatic hydrops)
[Ménière’s] Audiogram
Low- to mid-frequency sensorineural loss "An audiogram is required for all patients with suspected Ménière disease." Definite disease per NIDCD: "Two or more spontaneous episodes of vertigo lasting 20 minutes to 12 hours," documented low-to-medium-frequency hearing loss, and symptoms "not accounted for by another diagnosed balance-related condition."
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[Ménière’s] MRI or CT of the brain
Rules out other causes NIDCD: imaging "may be recommended" "To rule out other diseases."
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[Sudden hearing loss] Hearing test NIDCD
Loss of at least 30 dB in three connected frequencies within 72 hours Rule out conductive causes such as wax or fluid first; with one-sided loss, "tumors on the auditory nerve should be ruled out as the cause."
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Weber and Rinne tuning-fork tests
Conductive: bone conduction better than air (Rinne negative) "If bone conduction is superior to air conduction (Rinne negative), a conductive hearing loss is present." For presbycusis, StatPearls says these tests "should not be used as screening or diagnostic tools" — audiometry diagnoses.
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[Age-related] Screening question
Ask about hearing problems; low threshold for audiometry "There should be a low threshold for referral for definitive auditory testing in patients suspected of presbycusis."
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Cataracts & Post-op Eye Care Cataract
Dilated eye exam
Cloudy lens. "If you’re age 60 or older, get a dilated eye exam every 1 to 2 years."
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Red reflex (infants)
Asymmetric or absent red reflex, white pupil. Parents may notice a white cataract; poor tracking or eye contact are signs of poor vision.
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Pre-op eye measurements
Size and shape of the eye measured to choose the IOL. "About a week before your surgery, your eye doctor will do some tests to measure the size and shape of your eye."
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Intraocular pressure on steroid drops
May rise with prolonged use. "If DUREZOL is used for 10 days or longer, IOP should be monitored."
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Retinal Detachment & Macular Degeneration Retinal detachment
Dilated eye exam
Retinal tear or detachment; macular changes in AMD. For suspected RD, a dilated fundus exam with indirect ophthalmoscopy by an eye specialist. A dilated exam can find a small tear "early, before it starts to affect your vision."
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Ultrasound or OCT (optical coherence tomography)
Shows detachment when the view is limited; OCT images the macula in AMD.
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Amsler grid
Wavy lines (metamorphopsia) or missing areas (scotoma). Home self-check for people with drusen — any new change means contacting the ophthalmologist immediately.
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Intraocular pressure after intravitreal injection
May rise acutely within 60 minutes.
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Conjunctivitis (Pink Eye) Pink eye
Clinical examination and history
Diagnosis is usually clinical CDC: "Healthcare providers can usually identify pink eye by examining the eye while considering patient history and other symptoms." "Visual acuity and pupillary exams are important for all ocular complaints" (StatPearls). Examine with hand hygiene and gloves because infectious conjunctivitis is highly contagious (StatPearls).
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Red-flag screen: pain, photophobia, vision, pupils, corneal clarity
Normal vision and pupils; no ciliary flush, hypopyon or hyphema StatPearls: sectoral redness, ciliary flush, raised eye pressure, vision loss, moderate to severe pain, hypopyon, hyphema, pupil asymmetry and trouble keeping the eye open "point to a diagnosis other than conjunctivitis."
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[BAC] Conjunctival culture and Gram stain
Reserved for suspected gonococcal, meningococcal or chlamydial infection, recurrence or treatment failure StatPearls: cultures are not needed in most cases, but "conjunctival cultures should also be obtained in recurrent conjunctivitis and conjunctivitis refractory to treatment." Suspected meningococcal conjunctivitis "should be empirically treated with systemic antibiotics, even if culture results are pending."
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[STI] Evaluation for sexually transmitted infection CDC STI Treatment Guidelines 2021
Genital testing and partner referral when gonorrhea or chlamydia is suspected CDC: "Presenting with chlamydial conjunctivitis will have an associated genital infection." CDC STI Guidelines (2021): "Patients should be instructed to refer their sex partners for evaluation and treatment."
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Diabetic Retinopathy DR
Comprehensive dilated eye exam NEI, CDC, NIDDK
At least once a year for everyone with diabetes NEI: "If you have diabetes, it’s important to get a comprehensive dilated eye exam at least once a year." NIDDK: "Your eyes may seem fine, but having a full, dilated eye exam is the only way to know for sure." The exam "is simple and painless" (NEI).
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When to have the first exam CDC
Type 2: at diagnosis. Type 1: within 5 years of diagnosis (CDC) CDC: "You should have an eye exam to check for DR immediately if you're diagnosed with type 2 diabetes. For type 1 diabetes, you should have an eye exam within 5 years of diagnosis." [PREG] NEI: "If you have diabetes and are pregnant, have a comprehensive dilated eye exam as soon as possible."
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Follow-up by stage StatPearls, NEI
StatPearls: very mild NPDR yearly; mild to moderate NPDR every 6 to 12 months; severe NPDR within 2 to 4 months NEI: "Some people with diabetic retinopathy may need a comprehensive dilated eye exam as often as every 2 to 4 months."
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Fluorescein angiography and OCT NEI, StatPearls
Angiography maps leaking or closed vessels; OCT measures retinal thickening NEI: a fluorescein angiogram "lets the doctor see pictures of the blood vessels in your retina." OCT is used "To evaluate retinal thickening" and "For the assessment and monitoring of edema after initiation of treatment"; OCT angiography "is especially useful in patients with kidney disease and patients prone to an anaphylactic reaction to the dyes" (StatPearls).
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AI screening StatPearls
Autonomous software can detect more-than-mild retinopathy "FDA has approved a software program IDx-DR for the detection of 'more than mild diabetic retinopathy' or its absence in 2018" (StatPearls).
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HbA1c and systemic work-up StatPearls
StatPearls: "HbA1c level should be kept below 7%." "Diabetes affects almost all the major organs of the body. Hence a thorough systemic examination should be done to rule out diabetic complications" (StatPearls).
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Oncology

Oncologic Emergencies
TLS panel (K⁺, phosphorus, uric acid, calcium) Cairo–Bishop
Laboratory TLS = ≥ 2 within 24 h: uric acid ≥ 8.0 mg/dL · K⁺ ≥ 6.0 mEq/L · phosphorus ≥ 4.5 mg/dL · calcium ≤ 7.0 mg/dL (or a 25% change from baseline in each) Monitoring cadence after starting therapy: every 4–6 h for high-risk patients, every 8–12 h intermediate, daily low risk. Clinical TLS adds creatinine > 1.5× normal, seizure, or arrhythmia
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Absolute neutrophil count (ANC)
Neutropenia < 1,500/µL · severe < 500/µL · profound < 100/µL Below 500/µL is severe neutropenia, where infection risk is highest; empiric antibiotics for febrile neutropenia continue until ANC recovers to ≥ 500/mm³ and/or the infection clears
Normal ≥ 1,500 cells/µL
Blood cultures × 2 (febrile neutropenia) IDSA (per StatPearls)
Drawn from a peripheral vein plus every lumen of every venous catheter, before antibiotics Culturing must never delay treatment — empiric broad-spectrum antibiotics start within 1 hour of triage; door-to-needle beyond 60 minutes is associated with ICU admission
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Gadolinium-enhanced MRI, entire spine (suspected MSCC) StatPearls
Gold standard — sensitivity 93%, specificity 97%; done immediately, not scheduled CT myelography if MRI is unavailable. Metastasis characteristically spares the intervertebral disc space, unlike infection
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Contrast chest CT (suspected SVC syndrome) StatPearls
Obstruction with collateral vessels — sensitivity 96%, specificity 92%; venography is the gold standard Duplex ultrasound screens the jugular, subclavian, and innominate veins for catheter-related thrombus
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Serum calcium (corrected) + ECG StatPearls
Mild 10–12 mg/dL · moderate 12–14 · severe > 14 mg/dL = crisis; ECG shows a shortened QT interval (± PR prolongation, wide QRS, bradyarrhythmias) Correct for albumin: measured Ca + 0.8 × (4 − albumin g/dL); use ionized calcium when accuracy matters (~45% of calcium is protein-bound)
Normal 8.9–10.1 mg/dL
Cancer Fundamentals & Treatment Care Oncology basics
Staging — what it is and what it decides
"Stage refers to the EXTENT of your cancer, such as HOW LARGE the tumor is and IF IT HAS SPREAD." Every staging system includes "where the TUMOR IS LOCATED · the SIZE of the tumor · whether the cancer has spread to NEARBY LYMPH NODES · whether the cancer has spread to a DIFFERENT PART OF THE BODY" Knowing the stage "helps your doctor UNDERSTAND HOW SERIOUS your cancer is and your CHANCES OF SURVIVAL, PLAN THE BEST TREATMENT for you, and IDENTIFY CLINICAL TRIALS that may be treatment options." Note that there is no single system: "there are MANY staging systems. Some, such as the TNM staging system, are used for many types of cancer. Others are specific to a particular type of cancer" — and "examples of cancers with DIFFERENT staging systems include BRAIN AND SPINAL CORD TUMORS AND BLOOD CANCERS."
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The TNM system
"The T refers to the SIZE AND EXTENT OF THE MAIN TUMOR… The N refers to the NUMBER OF NEARBY LYMPH NODES THAT HAVE CANCER. The M refers to WHETHER THE CANCER HAS METASTASIZED." T: TX: cannot be measured · T0: cannot be found · T1 to T4: size and extent, the higher the number, the larger the tumor or the more it has grown into nearby tissues. N: NX: cannot be measured · N0: no cancer in nearby nodes · N1 to N3: the higher the number, the more lymph nodes contain cancer. M: MX: cannot be measured · M0: has not spread · M1: has spread. Worked examples: T1N0MX or T3N1M0 It is "the MOST WIDELY USED cancer staging system. Most hospitals and medical centers use the TNM system as their main method for cancer reporting." Letters may subdivide for detail — "such as T3a and T3b." Read a TNM string as three separate questions: how big, how many nodes, has it left.
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Stage groupings and the registry categories
Stage 0: "Abnormal cells are present but have not spread to nearby tissue. Also called carcinoma in situ, or CIS." Stage I, Stage II, and Stage III: "Cancer is present. The higher the number, the larger the cancer tumor and the more it has spread into nearby tissues." Stage IV: "The cancer has spread to distant parts of the body." Sub-lettering follows the same idea — "stage 2 prostate cancer may be further divided into 2A, 2B, or 2C." The five-category registry system runs in situ · localized · regional · distant · unknown The registry categories are "more often used by cancer registries than by doctors" — but they are the vocabulary behind every published survival statistic a patient will find online, so knowing which language a number is written in matters.
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The stage at diagnosis is the stage forever
"A cancer is ALWAYS REFERRED TO BY THE STAGE IT WAS GIVEN AT DIAGNOSIS, EVEN IF IT GETS WORSE OR SPREADS. New information about how a cancer has changed over time is ADDED TO the original stage. SO THE STAGE DOESN’T CHANGE, EVEN THOUGH THE CANCER MIGHT" This one reliably surprises students and patients alike. A stage II cancer that later metastasises is documented as stage II with metastatic disease, not restaged as IV. Explaining it in advance prevents a family reading a chart and concluding that someone made an error.
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Pathology of a metastatic lesion
"Metastatic cancer cells GENERALLY LOOK THE SAME as cells of the original cancer… metastatic cancer cells and cells of the original cancer usually have some MOLECULAR FEATURES IN COMMON, such as the presence of SPECIFIC CHROMOSOME CHANGES" "THIS IS HOW DOCTORS CAN TELL that it is cancer that has spread" rather than a second, new primary — and it is the evidence behind the naming rule. The practical consequence is that the biopsy result, not the location of the lesion, decides what the disease is called and how it is treated.
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Colorectal cancer screening — USPSTF, 18 May 2021
Adults 50 to 75 — screen. GRADE A. Adults 45 to 49 — screen. GRADE B. Adults 76 to 85 — "SELECTIVELY OFFER" screening, because "the NET BENEFIT of screening ALL persons in this age group is SMALL." GRADE C. Strategies include "HSgFOBT or FIT EVERY YEAR · stool DNA-FIT EVERY 1 TO 3 YEARS," with colonoscopy every 10 years, flexible sigmoidoscopy every 5 years and CT colonography every 5 years The change worth knowing: "the USPSTF EXPANDED the recommended ages for colorectal cancer screening to 45 to 75 years (PREVIOUSLY, IT WAS 50 TO 75 YEARS)." It applies to average-risk adults without symptoms — no prior colorectal cancer or adenomatous polyps, no inflammatory bowel disease, and no personal or family history of predisposing genetic disorders.
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Breast cancer screening — USPSTF, 30 April 2024
"The Task Force recommends that ALL WOMEN GET SCREENED FOR BREAST CANCER EVERY OTHER YEAR, STARTING AT AGE 40 AND CONTINUING THROUGH AGE 74, to reduce their risk of dying from this disease. THIS IS A B GRADE" This edition replaced the individualised-decision approach, in the Task Force’s own words: "PREVIOUSLY, WE RECOMMENDED THAT WOMEN IN THEIR 40s MAKE AN INDIVIDUAL DECISION WITH THEIR CLINICIAN… The Task Force NOW recommends that all women start getting screened… EVERY OTHER YEAR STARTING AT AGE 40." Nearly half of all women have DENSE BREASTS, "which INCREASES THEIR RISK for breast cancer and means that MAMMOGRAMS MAY NOT WORK AS WELL for them" — they should still start at 40 and discuss follow-up testing. Older textbooks and even recently updated review chapters still print "50 to 74 biennial, 40 to 49 individualized." That is the superseded recommendation.
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Cervical and lung cancer screening — read the statements themselves
The USPSTF also issues cervical and lung cancer screening recommendations, and this page does not print their figures. The ages, intervals, grades and smoking-history bands for both must be read from the current USPSTF final recommendation statements, which are the only place they can be relied on Why a page that gives colorectal and breast in full stops short here: those two statements are cited below and these two are not, and a number without a listed source is a number you cannot check. The risk is concrete rather than theoretical — widely used review chapters still print superseded USPSTF figures for lung and breast screening, so a reader who meets a different number has no way to tell which edition it came from. One thing is worth carrying anyway, because it is not a figure: the cervical recommendation is under revision by the Task Force, so anything quoted for it needs its date checked before it is used.
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Head & Neck Cancer Head and neck squamous cell carcinoma (HNSCC)
Screening NCI
No standard or routine screening test "Although there is no standard or routine screening test for head and neck cancers, dentists may check the oral cavity for signs of cancer during a routine checkup" (NCI). NIDCR: "Your regular dental checkup is an excellent opportunity to have the examination."
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Laryngoscopy with biopsy; fine-needle aspiration of a node
Squamous cell carcinoma on tissue "Multiple methods for obtaining tissue are feasible, including biopsy during direct laryngoscopy of the suspected primary lesion and fine-needle aspiration cytology for suspected nodal disease" (StatPearls). StatPearls: "A referral to an ENT surgeon should be considered if hoarseness persists and is accompanied by other signs suggestive of malignancy."
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HPV status (oropharyngeal cancer)
HPV-positive or HPV-negative HPV-positive oropharyngeal tumors have "a much better prognosis and higher chance of complete cure" (NCI).
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[CIS] Before cisplatin — kidney function, electrolytes, hearing test
Baseline creatinine, BUN, creatinine clearance, magnesium, sodium, potassium, calcium; audiometry Cisplatin label: renal toxicity is cumulative; "Audiometric testing should be performed prior to initiating therapy and prior to each subsequent dose of drug."
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[CET] During and after cetuximab — magnesium, potassium, calcium
Watch for low magnesium and related electrolyte losses ERBITUX label: monitor "during treatment and for at least 8 weeks following the completion. Replete electrolytes as necessary."
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[RT] Thyroid function after neck radiation
Rising risk of hypothyroidism NCI: "The doctor may monitor thyroid and pituitary gland function, especially if the head or neck was treated with radiation."
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A study aid — reference ranges vary by laboratory, age and assay. The small mono label under a test names the guideline that owns the value; each disorder page cites its sources.

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