Polycythemia vera (PV) is a chronic that is characterized by an erythropoietin-independent, irreversible increase in erythrocyte, granulocyte, and platelet counts. The elevated blood cell mass results in hyperviscosity, which is associated with slow blood flow and an increased risk of thrombosis. The disorder typically initially has a long asymptomatic period, then assumes a chronic, insidious course. Clinical features include facial flushing, pruritus, erythromelalgia, headaches, and dizziness. Severe complications such as thrombotic events (e.g., stroke, Budd-Chiari syndrome) may occur. Since PV is an incurable disorder, the primary goals of management involve controlling RBC mass and reducing the risk of thrombotic complications. Periodic phlebotomy reduces the amount of circulating cells and is therefore the treatment of choice.
- The JAK2 (Janus kinase 2) oncogene codes for a non-receptor tyrosine kinase in hematopoietic progenitor cells. JAK2 is essential for the regulation of erythropoiesis, thrombopoiesis (megakaryopoiesis), and granulopoiesis.
- 95% of primary PV patients have a mutation in the JAK2 gene (gain of function) → ↑ tyrosine kinase activity → erythropoietin-independent proliferation of the myeloid cell lines → ↑ blood cell mass (erythrocytosis, thrombocytosis, and granulocytosis) → hyperviscosity and slow blood flow → ↑ risk of thrombosis and poor oxygenation.
- Often asymptomatic (incidental finding on routine blood tests)
- Constitutional symptoms: weight loss, fatigue, sweating
- Hyperviscosity syndrome (triad of mucosal bleeding, neurological symptoms, and visual changes)
- Pruritus: Itching typically worsens when the skin comes into contact with warm water (aquagenic pruritus).
- Nonspecific neurological symptoms : dizziness, headache, visual disturbances, tinnitus
- Splenomegaly : associated with early satiety and abdominal discomfort; less commonly hepatomegaly
- Peptic ulcer disease
- Symptoms of thrombotic and hemorrhagic complications (see “Complications” below)
Patients with PV are at increased risk of thrombosis and bleeding.
- ↑ Hb/Hct, ↑ RBCs
- ↑ Platelets (> 450,000/μL)
- ↑ Leukocytes (> 12,000/μL)
- ↑ Uric acid, ↑ LDH
- ↑ Leukocyte alkaline phosphatase
- ↓ Serum iron levels
- ↓ ESR
- ↓ EPO
- Arterial O2 saturation: normal
Diagnostic criteria (WHO 2016) 
A diagnosis of polycythemia vera requires:
All three major criteria
- The first two major criteria AND the minor criterion
|Differential diagnoses of secondary erythrocytosis|
|EPO||Expected plasma volume||RBC mass||Oxygen saturation||Underlying conditions|
|Relative polycythemia|| || || || |
|Appropriate absolute polycythemia|| || || || || |
|Inappropriate absolute polycythemia|| || || || |
- Other causes may present with normal or even decreased endogenous EPO levels.
The differential diagnoses listed here are not exhaustive.
Phlebotomy (mechanical reduction in the number of red cells)
- Periodic removal of blood via venapuncture temporarily reduces cell counts and hyperviscosity.
- 250–500 mL in intervals of 2–3 days until a HCT of ≤ 0.45 is established 
- Antiplatelet prophylaxis: aspirin
- Phlebotomy (mechanical reduction in the number of red cells)
- Cytoreductive therapy (medical reduction in the number of blood cells)
- Supportive: antihistamines (pruritus), allopurinol (gout prophylaxis), PPIs or H2-blockers (peptic ulcer prophylaxis)
Polycythemia vera is a life-threatening disease because of the numerous complications associated with it.
- Venous thrombosis
- Arterial thrombosis
- High number of cell turnover → increased uric acid
- ( ), ( ): Additional genetic mutations may cause polycythemia vera to transition to other hematological diseases.
- Myelofibrosis: fibrotic transformation of the bone marrow
We list the most important complications. The selection is not exhaustive.