Polycythemia Vera
PV Verified · Sep 2026Polycythemia vera is a myeloproliferative neoplasm in which uncontrolled red blood cell production — usually driven by a JAK2 gene change — raises red cell mass, often with high white cell and platelet counts, thickening the blood and raising the risk of thrombosis.
JAK2 turns the marrow “on” without erythropoietin; thick blood causes headaches, itching after a hot shower and clots; primary versus secondary polycythemia by EPO level; phlebotomy with no iron supplements; low-dose aspirin; and cytoreduction — hydroxyurea, interferon, ruxolitinib — with the interferon mood warning.
What’s going wrong in the body
The normal physiology, where it fails, and why the body’s compensation backfires.
01 JAK2 switches the marrow on — all three cell lines rise
"Polycythemia vera (PV) is a myeloproliferative neoplastic disorder involving uncontrolled red blood cell production resulting in elevated red blood cell (RBC) mass." "There is often a concurrent stimulation of myeloid and megakaryocytic lineages, leading to increased white blood cell and platelet production." NHS: "It’s a slow-growing type of blood cancer," and "Although caused by a genetic change, polycythaemia vera isn’t usually inherited."
The switch is JAK2. The V617F change "leads to constitutively active cytokine receptors." Sources give slightly different frequencies: StatPearls (2023) says JAK2 is "mutated in 90% of cases"; StatPearls (2026) says "The primary defect in nearly 95% of cases of polycythemia vera is an acquired mutation in exon 14." "The bone marrow of patients with polycythemia vera (PV) contains normal stem cells and contains abnormal clonal stem cells that suppress normal stem cell growth and maturation."
EPO is low, not high — the ICC minor criterion is "Serum erythropoietin level below reference range." That is the key contrast with secondary polycythemia.
02 Thick blood — clots, itching, a full spleen, and sometimes bleeding
Hyperviscosity. NHS: "This makes the blood thicker and less able to travel through blood vessels and organs. Many of the symptoms of erythrocytosis are caused by this sluggish flow of blood." "Hyperviscosity increases the risk of both arterial and venous thrombosis." NCI: "This can increase the risk of stroke or heart attack." "Thrombosis is a major complication of polycythemia vera (PV)."
Why bleeding too. "Patients with platelets greater than 1 million/microliter can have increased bleeding risk due to acquired von Willebrand disease and, therefore, should not be placed on aspirin."
Itch after water. "Aquagenic pruritus, which occurs during or after a hot shower, is a complaint in 40% of patients." "The mechanism is likely from mast cell and basophil degranulation, causing a histamine surge." (The 2026 StatPearls chapter calls post-shower pruritus infrequent.) Basophil histamine also explains the GI complaints: "GI discomfort and peptic ulcer disease are common, likely from increased histamine release from basophils and increased viscosity in gastrointestinal blood supply."
The spleen fills. "These extra blood cells may collect in the spleen and cause it to swell." "Early satiety occurs from impaired gastric filling due to splenomegaly."
03 Primary versus secondary — and why phlebotomy works
Rule out the common causes first. "Secondary polycythemia (from hypoxia or smoking) is much more common than primary PV and must be ruled out before the diagnosis of primary PV can be made." Secondary causes raise EPO — altitude, lung disease, smoking or carbon monoxide ("Usually seen in individuals who smoke tobacco or those with occupational exposure"), and "Erythropoietin analog administration, anabolic steroids, or testosterone replacement therapy." NHS also describes apparent erythrocytosis, which "is often caused by being overweight, smoking, drinking too much alcohol or taking certain medicines."
Phlebotomy works by making the marrow iron-deficient. "The goal of phlebotomy is to deliberately induce an iron-deficient state, which will, to some degree, limit the marrow’s capacity for erythropoiesis; therefore, patients should not take iron supplements." NCI: the primary therapy uses "phlebotomy or cytoreductive therapy to maintain the hematocrit below 45%," a target that gave "lower rates of cardiovascular death and major thrombosis."
No cure. "There is no cure for polycythemia vera (PV); treatment goals are aimed at symptom relief and reducing the risk of disease complications, including thrombosis, bleeding, and hematologic transformation."
Causes & risk factors
Modifiable factors are teaching targets — the patient can act on them.
Signs & symptoms
Each finding tied to the mechanism that produces it — and the triage it calls for.
Diagnostics
Complications
Medications for this condition
Why each class is prescribed here — every card links to its full pharmacology page.
Low-dose aspirin prevents clots in most patients. NCI: low-dose aspirin daily "unless contraindicated by major bleeding or gastric intolerance"; StatPearls (2026): "low-dose aspirin is recommended for most patients without contraindications." Not when platelets exceed 1 million/µL (acquired von Willebrand disease), and higher doses raise bleeding risk. It also relieves erythromelalgia.
After a clot. "In the setting of a first thrombotic event, an appropriate dose and length of anticoagulation are recommended." "There is currently no difference in treatment recommendations for patients with underlying PV." Anticoagulation adds bleeding risk.
Cytoreduction for high-risk disease or when phlebotomy is not enough. Hydroxyurea — the sources place it differently: StatPearls (2023) calls it "The first-line agent" for cytoreduction in high-risk patients; StatPearls (2026) says it "is usually considered second-line therapy" after phlebotomy (poor venous access, high phlebotomy need, severe thrombocytosis, intractable pruritus). Adverse effects: "cytopenias, oral ulcers, GI upset, peripheral neuropathy, and rare but severe pulmonary toxicity"; NHS: do not take it "if you’re pregnant or trying to become pregnant." Ropeginterferon (Besremi) is indicated for "adults with polycythemia vera"; boxed neuropsychiatric warning; "Can cause fetal harm." On pregnancy the sources differ — NHS says interferon "can be taken in pregnancy," StatPearls says higher-risk pregnant patients "may require the addition of pegylated interferon-α" — but the Besremi label warns it "Can cause fetal harm." Ruxolitinib (Jakafi) — for PV with "an inadequate response or are intolerant of hydroxyurea"; watch counts, infection (including tuberculosis), skin cancer and thrombosis, and do not stop it abruptly — symptoms "may flare."
Pruritus. "To manage pruritus, initial treatment should include antihistamines and selective serotonin reuptake inhibitors (SSRIs)." Interferon, then JAK inhibitors, follow for resistant itch.
Pruritus — an initial option alongside antihistamines (StatPearls).
"Allopurinol and febuxostat may be required in patients with significant hyperuricemia." NHS lists gout among PV symptoms.
AVOID in PV. Phlebotomy works by inducing iron deficiency — "patients should not take iron supplements."
Beyond medications
- Therapeutic phlebotomy (venesection) — "Therapeutic phlebotomy is the primary treatment of choice for Polycythemia Vera." NHS: "Venesection involves removing about 1 pint (half a litre) of blood at a time"; "At first, you may need the treatment every week, but once your erythrocytosis is under control you should need it less often." StatPearls (2026): sessions continue weekly "until a target hematocrit of less than 45% is achieved."
- Tailor the volume — "Men may tolerate up to the removal of 1.5 to 2 units a week," whereas "women, the elderly, those who weigh less than 50 kg, or those with cardiovascular disease may only tolerate removal of 0.5 units a week."
- Phlebotomy side effects over time — "Thrombocytosis and symptoms related to chronic iron deficiency, including pica, angular stomatitis, and glossitis"; spleen enlargement and itch "may persist despite control of the hematocrit by phlebotomy."
- No blood donation — "Patients with polycythemia vera must be discouraged from donating blood"; donor blood from PV "is not accepted for donation in most countries."
- Cardiovascular risk reduction — "weight loss, exercise, tobacco cessation, blood pressure control." NHS: "being overweight or smoking only increases this risk."
- Splenectomy only in selected cases — "may be appropriate in the setting of painful splenomegaly or recurrent splenic infarcts."
Nursing considerations
The RN-specific layer — each action paired with the reason it matters.
How a real nurse thinks
The clinical-judgment loop, worked for a typical presentation — reasoning, not reference.
- 1 Recognize cues
He is lightheaded on standing with a fall in blood pressure and rise in heart rate just after phlebotomy, and he is older with cardiovascular disease. He also wants to take iron.
- 2 Analyze cues
This is an orthostatic response to volume removal. StatPearls: "Older patients and those with cardiovascular disease should have a smaller volume of blood removed during phlebotomy sessions to minimize orthostatic effects." Iron would undo the treatment, whose goal is "to deliberately induce an iron-deficient state."
- 3 Prioritize
Safety first: lie him down to prevent a fall, then report the orthostatic change. The iron question is important teaching but not urgent.
- 4 Generate solutions
Return him to a lying position, recheck vital signs, notify the provider and give normal saline if ordered — "Normal saline may be given post phlebotomy to replace the volume lost." Ask the team to consider a smaller volume next session. Teach no iron supplements, hydration and no strenuous activity for 24 hours.
- 5 Take action
SBAR: 66-year-old man with PV and CAD, 500 mL phlebotomy 15 minutes ago; standing BP 108/66, HR 98 (lying 132/78, 76), lightheaded, no syncope. Requesting saline order and review of phlebotomy volume. Saline is given; he rests supine.
- 6 Evaluate
Thirty minutes later he stands without symptoms and his standing vital signs are near baseline. He repeats back that he must not take iron, will drink fluids and avoid heavy exertion today, and will seek emergency help for leg swelling, chest pain, breathlessness or stroke signs.
Scenario — you’re the nurse
Work each question before revealing the answer. Rationales explain the wrong options too.
A 66-year-old man with JAK2-positive polycythemia vera and a history of coronary artery disease had 500 mL removed by therapeutic phlebotomy 15 minutes ago. His pre-procedure hematocrit was 52%. He takes low-dose aspirin. As he stands to leave he says he feels lightheaded, and asks whether he should start an iron tablet his neighbour recommended ‘because I always feel tired’.
Q1 Multiple choice Right after phlebotomy, a patient with PV and heart disease becomes lightheaded on standing, with BP down and HR up. What is the nurse’s first action? - A. Have him lie down and recheck vital signs
- B. Encourage him to walk to improve circulation
- C. Give his usual aspirin dose
- D. Schedule the next phlebotomy for tomorrow
Reveal answer & rationale
Q2 Multiple choice The patient asks about taking an iron tablet because he feels tired. Which response is correct? - A. ‘Yes — phlebotomy makes you anemic, so iron helps.’
- B. ‘No — phlebotomy works partly by lowering your iron so the marrow makes fewer red cells.’
- C. ‘Only take iron on the days you have phlebotomy.’
- D. ‘Iron is fine as long as you also take aspirin.’
Reveal answer & rationale
Q3 Select all that apply Which findings in a patient with polycythemia vera need emergency help? Select all that apply. - A. A painful, swollen, red calf
- B. Sudden breathlessness and chest pain
- C. Sudden weakness of one side of the face and arm
- D. Itching after a hot shower
- E. Coughing up blood
Reveal answer & rationale
Q4 Multiple choice Which laboratory pattern best supports primary polycythemia vera rather than secondary polycythemia? - A. High hematocrit with high erythropoietin
- B. High hematocrit, JAK2 mutation and low erythropoietin
- C. High hematocrit with high carboxyhemoglobin
- D. Low hematocrit with high platelets
Reveal answer & rationale
Q5 Select all that apply A patient starting ropeginterferon (Besremi) asks what to watch for. Which teaching is accurate? Select all that apply. - A. Report new or worsening low mood to the provider right away
- B. Stop the medicine and seek immediate medical attention for suicidal thoughts
- C. Keep up good oral hygiene and dental checks
- D. It is safe in pregnancy, so no precautions are needed
Reveal answer & rationale
Common questions
What causes polycythemia vera?
What are the early signs of polycythemia vera?
Which findings should a nurse report immediately in polycythemia vera?
Why take blood out instead of giving medicine?
Is polycythemia vera cancer?
Is hydroxyurea first-line?
Sources
- Polycythemia Vera — StatPearls — StatPearls (NCBI Bookshelf)
- Polycythemia — StatPearls — StatPearls (NCBI Bookshelf)
- Phlebotomy — StatPearls — StatPearls (NCBI Bookshelf)
- Myeloproliferative Neoplasms Treatment (PDQ®) — Health Professional Version — National Cancer Institute
- Chronic Myeloproliferative Neoplasms Treatment (PDQ®) — Patient Version — National Cancer Institute
- Erythrocytosis — NHS. Contains public sector information licensed under the Open Government Licence v3.0 (https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/) — NHS (UK)
- JAKAFI (ruxolitinib) — FDA label — U.S. FDA / NLM DailyMed
- BESREMi (ropeginterferon alfa-2b-njft) — FDA label — U.S. FDA / NLM DailyMed
Reviewed by Hae Suk Lee, RN
Educational summary for nursing students. Scenarios are fictional teaching cases. Always verify against current guidelines and your institution's protocols before acting in practice. Not medical advice.