Lab values & drug levels

A high-yield NCLEX table. It keeps two things separate: a therapeutic drug level is the target you dose the drug to reach (digoxin, lithium); a normal range is the healthy baseline you monitor to stay within (LFTs, potassium). Values are typical adult figures for orientation — always read against your facility's reference range and the patient's clinical picture.

47 monitored levels

Test · drug class Therapeutic / normal Toxic / critical

Absolute neutrophil count (ANC) Monitor with the CBC to track neutrophil recovery Colony-Stimulating Factors

Normal range ≥ 1,500/µL (normal ~2,500–7,000)

Toxic / critical —

aPTT (heparin) q6h until stable on IV heparin Anticoagulants

Therapeutic 1.5–2× normal (or anti-Xa)

Toxic / critical —

AST / ALT (LFTs) If overdose or chronic/high-dose use Acetaminophen (Non-Opioid Analgesic)

Normal range AST 10–40 · ALT 7–56 U/L

Toxic / critical —

Blood glucose Before meals & bedtime; match insulin to glucose/meal Insulins

Therapeutic ~70–180 mg/dL (varies by goal)

Toxic / critical < 70 mg/dL = hypoglycemia — treat immediately

Blood glucose Monitor, esp. diabetics Corticosteroids

Normal range Fasting 70–99 mg/dL

Toxic / critical Steroids raise glucose (hyperglycemia)

Blood pressure Monitor regularly — ESAs can raise/worsen hypertension Erythropoiesis-Stimulating Agents (ESAs)

Normal range < 120/80 mmHg (normal)

Toxic / critical —

Calcium Monitor Thiazide Diuretics

Normal range 8.5–10.2 mg/dL

Toxic / critical Hypercalcemia (thiazides retain calcium)

Carbamazepine level Trough; also monitor CBC and sodium Anticonvulsants

Therapeutic 4–12 mcg/mL

Toxic / critical > 12 mcg/mL — diplopia, ataxia, nystagmus; severe (seizures, coma) > 25

CBC & LFTs (± renal function) Baseline & periodically on methotrexate — detects **myelosuppression/hepatotoxicity** Immunosuppressants / Biologics / DMARDs

Normal range WBC 5,000–10,000 · Hgb 12–17 · Plt 150,000–400,000/µL; AST 10–40 · ALT 7–56 U/L

Toxic / critical —

Clozapine — absolute neutrophil count (ANC) Weekly for the first 6 months, then less frequently (agranulocytosis surveillance) Antipsychotics

Normal range Baseline ≥ 1500/µL (≥ 1000 for benign ethnic neutropenia)

Toxic / critical < 500/µL = severe neutropenia — stop clozapine

Creatine kinase (CK) Check if the patient reports muscle pain, tenderness, or weakness Statins

Normal range ~30–200 U/L

Toxic / critical > 10× ULN with muscle symptoms → rhabdomyolysis; stop the statin

Digoxin level Draw ≥ 6–8 h after a dose (steady state) Cardiac Glycosides (Digoxin)

Therapeutic 0.5–2 ng/mL (HF target 0.5–0.9)

Toxic / critical > 2.4 ng/mL

Electrolytes (K⁺, Na⁺) Baseline & routinely — loop/thiazide lower K⁺, potassium-sparing agents raise it Diuretics

Normal range K⁺ 3.5–5.0 · Na⁺ 135–145 mEq/L

Toxic / critical —

Glucose Monitor, esp. in diabetics Thiazide Diuretics

Normal range Fasting 70–99 mg/dL

Toxic / critical Hyperglycemia ("hyperGLUC")

Hemoglobin (Hgb) Hold/reduce the dose if it approaches 11 g/dL or rises too fast Erythropoiesis-Stimulating Agents (ESAs)

Therapeutic Do not exceed ~11 g/dL

Toxic / critical —

INR (warfarin) Routine; more often when starting/adjusting Anticoagulants

Therapeutic 2.0–3.0 (2.5–3.5 mechanical mitral valve)

Toxic / critical > 4 → bleeding risk

LFTs (AST/ALT) Baseline & during **azole** therapy — azoles can be **hepatotoxic** Systemic Antifungals

Normal range AST 10–40 · ALT 7–56 U/L

Toxic / critical —

LFTs (hepatic function) Baseline & periodically — hepatotoxicity (boxed warning) Antiarrhythmics

Normal range AST 10–40 · ALT 7–56 U/L

Toxic / critical —

Lithium level Draw **12 h after the dose**; check frequently when starting Mood Stabilizers (Lithium)

Therapeutic 0.6–1.2 mEq/L (maintenance)

Toxic / critical > 1.5 mEq/L

Liver function tests (AST/ALT, bilirubin) Baseline & periodically — **isoniazid, rifampin, and pyrazinamide are hepatotoxic**; hold and notify for symptomatic hepatitis (nausea, dark urine, jaundice, RUQ pain). Antitubercular Agents

Normal range AST 10–40 · ALT 7–56 U/L · bilirubin < 1.2 mg/dL

Toxic / critical —

Liver function tests (transaminases) Baseline & periodically Statins

Normal range AST 10–40 · ALT 7–56 U/L

Toxic / critical > 3× ULN → discontinue the statin

Max daily dose Count **all** combination OTC products Acetaminophen (Non-Opioid Analgesic)

Therapeutic ≤ 4 g/day adult (≤ 3 g with hepatic risk/chronic use)

Toxic / critical Hepatotoxic above ceiling / acute overdose

Methotrexate dosing frequency Verify the schedule at every check — accidental daily dosing is a classic fatal error Immunosuppressants / Biologics / DMARDs

Therapeutic WEEKLY for autoimmune disease

Toxic / critical DAILY dosing is fatal (pancytopenia/mucositis)

Peak Draw **30 min after** the IV infusion ends Aminoglycosides

Therapeutic 5–10 mcg/mL (gentamicin, conventional dosing)

Toxic / critical > 12 mcg/mL

Phenytoin level Trough, just before the next dose; draw a **free (unbound) level** in low-albumin or renal-failure patients Anticonvulsants

Therapeutic 10–20 mcg/mL (narrow therapeutic index)

Toxic / critical > 20 mcg/mL — nystagmus, ataxia, then CNS depression

Platelets Baseline & periodically Anticoagulants

Normal range 150,000–400,000/µL

Toxic / critical Watch for HIT (heparin)

Potassium Baseline & routine Loop Diuretics

Normal range 3.5–5.0 mEq/L

Toxic / critical Hypokalemia common

Potassium Baseline & routine Thiazide Diuretics

Normal range 3.5–5.0 mEq/L

Toxic / critical Hypokalemia common

Potassium Baseline & routine Potassium-Sparing Diuretics

Normal range 3.5–5.0 mEq/L

Toxic / critical Hyperkalemia > 5.0 mEq/L

Potassium Confirm **urine output** before replacing Electrolyte & Fluid Replacement

Normal range 3.5–5.0 mEq/L

Toxic / critical < 3.5 or > 5.0 mEq/L

Potassium Monitor Corticosteroids

Normal range 3.5–5.0 mEq/L

Toxic / critical May fall (hypokalemia)

Potassium (K⁺) Before dosing & routinely Cardiac Glycosides (Digoxin)

Normal range 3.5–5.0 mEq/L

Toxic / critical Low K⁺ potentiates toxicity

Potassium / magnesium & renal function (SCr) During **amphotericin B** — it wastes **K⁺/Mg²⁺** and is **nephrotoxic** Systemic Antifungals

Normal range K⁺ 3.5–5.0 · Mg²⁺ 1.5–2.5 mEq/L · SCr 0.6–1.2 mg/dL

Toxic / critical —

Pulmonary — chest x-ray / PFTs Baseline — watch for pulmonary fibrosis / pneumonitis Antiarrhythmics

Normal range Clear CXR; normal DLCO at baseline

Toxic / critical —

QT interval / ECG Continuous telemetry — a lengthening QT warns of torsades Antiarrhythmics

Normal range QTc < 450 ms (M) / < 460 ms (F)

Toxic / critical > 500 ms → torsades de pointes risk

Renal function (SCr / BUN) Baseline & during therapy Aminoglycosides

Normal range SCr 0.6–1.2 · BUN 7–20 mg/dL

Toxic / critical —

Renal function (SCr) Baseline & during therapy Vancomycin (Glycopeptide)

Normal range SCr 0.6–1.2 mg/dL

Toxic / critical —

Serum magnesium (obstetric) With clinical checks (DTRs, RR, urine output) Magnesium Sulfate (Obstetric)

Therapeutic 4–7 mEq/L

Toxic / critical Loss of DTRs 8–10 · respiratory depression > 13 · cardiac arrest ~25 mEq/L

Serum sodium Monitor serum sodium with daily weights during therapy Pituitary / ADH Agents

Normal range 135–145 mEq/L

Toxic / critical Dilutional hyponatremia — headache, confusion, cerebral edema, seizures

Sodium & renal function Monitor Loop Diuretics

Normal range Na⁺ 135–145 mEq/L · SCr 0.6–1.2 mg/dL

Toxic / critical —

Theophylline level Check whenever a status change or interacting drug alters clearance Methylxanthines (Theophylline)

Therapeutic 10–20 mcg/mL (narrow therapeutic index)

Toxic / critical > 20 mcg/mL

Trough Draw **just before** the next dose Aminoglycosides

Therapeutic 0.5–2 mcg/mL

Toxic / critical > 2 mcg/mL

Trough Draw **before the 4th dose** Vancomycin (Glycopeptide)

Therapeutic 10–20 mg/L (modern AUC/MIC 400–600)

Toxic / critical > 20 → nephrotoxicity risk

TSH Periodic; titrate the dose to the TSH goal (recheck ~4–6 weeks after any change) Thyroid Agents

Normal range 0.4–4.0 mIU/L

Toxic / critical —

TSH (thyroid function) Baseline & periodically — amiodarone is iodine-rich (hypo- or hyperthyroidism) Antiarrhythmics

Normal range 0.4–4.0 mIU/L

Toxic / critical —

Uric acid Monitor in gout-prone patients Thiazide Diuretics

Normal range ~3.4–7.0 (M) / 2.4–6.0 (F) mg/dL

Toxic / critical Hyperuricemia → gout flare

Valproic acid level Trough; also monitor LFTs, ammonia, and platelets Anticonvulsants

Therapeutic 50–100 mcg/mL

Toxic / critical > 100 mcg/mL — sedation, tremor; CNS depression / coma at ≥ ~180

The middle column is tagged Therapeutic (a drug level you titrate to) or Normal range (a baseline you monitor). A dash means that side doesn't apply. Trough vs. peak timing matters — draw as noted. See each class page for the full monitoring plan.