Diagnostic Approach to Polycythemia Vera

Introduction to Polycythemia Vera

The American Society of Hematology recommends that a sustained increase of ≥2 g/dL hemoglobin from baseline warrants investigation for polycythemia vera, even if values remain within normal reference ranges 1
Persistent mild elevations in red blood cells, hemoglobin, and hematocrit lasting for a year can be an early sign of polycythemia vera and warrant immediate investigation with JAK2 mutation testing, as suggested by the European Hematology Association 2, 3

The World Health Organization diagnostic criteria for polycythemia vera require both major criteria plus 1 minor criterion, or the first major criterion plus 2 minor criteria, including hemoglobin ≥18.5 g/dL (men) or ≥16.5 g/dL (women), or hematocrit ≥49% (men) or ≥48% (women), and presence of JAK2 V617F or JAK2 exon 12 mutation, as recommended by the National Comprehensive Cancer Network 2, 1
Major criteria include hemoglobin ≥18.5 g/dL (men) or ≥16.5 g/dL (women), or hematocrit ≥49% (men) or ≥48% (women), and presence of JAK2 V617F or JAK2 exon 12 mutation, with a strength of evidence level of I (high) 2, 1
Minor criteria include bone marrow biopsy showing hypercellularity with trilineage growth (panmyelosis), serum erythropoietin below normal reference range, and endogenous erythroid colony formation in vitro, as suggested by the International Society for Experimental Hematology 2, 1

The initial laboratory workup should include JAK2 V617F mutation testing (exon 14), which is present in >95% of polycythemia vera cases, as recommended by the American College of Medical Genetics and Genomics 2, 1
If JAK2 V617F is negative, proceed to JAK2 exon 12 mutation testing, which captures the remaining ~3% of polycythemia vera cases, with a strength of evidence level of II (moderate) 2, 1
Serum erythropoietin (EPO) level should also be measured, as low EPO has >90% specificity for polycythemia vera, while elevated EPO suggests secondary polycythemia, as suggested by the Endocrine Society 3, 4, 1

If JAK2 mutation is negative and EPO is elevated or normal, systematically evaluate for secondary causes, including hypoxia-driven causes such as smoking history, obstructive sleep apnea, chronic lung disease (COPD), and cyanotic congenital heart disease, as recommended by the American Thoracic Society 3, 4
Hypoxia-independent causes include EPO-producing tumors, testosterone use, and post-renal transplant erythrocytosis, with a strength of evidence level of III (low) 5, 4

Immediate referral to hematology is indicated if JAK2 mutation is positive, hemoglobin >20 g/dL with symptoms of hyperviscosity, unexplained splenomegaly, or diagnosis remains unclear after initial workup, as recommended by the American Society of Hematology 3

The World Health Organization recommends a hemoglobin cutoff of ≥18.5 g/dL in men and ≥16.5 g/dL in women for diagnosing polycythemia vera, representing the 99th percentile of method-specific reference ranges adjusted for age, sex, and altitude of residence 6, 7

The World Health Organization and Mayo Clinic guidelines suggest that in patients with a history of deep vein thrombosis, the same hemoglobin cutoffs apply, but the diagnostic threshold for suspicion should be lower, and a workup for polycythemia vera should be pursued if hemoglobin or hematocrit values are above the 95th percentile for sex and race, or if there is a documented sustained increase of ≥2 g/dL hemoglobin from baseline 6, 8, 9
The Mayo Clinic guidelines identify unusual thrombosis, including DVT, as a polycythemia vera-related feature that warrants investigation even when hemoglobin/hematocrit values are borderline-high or within the upper-normal range 8, 9

Iron deficiency can mask true polycythemia and must be excluded before dismissing the diagnosis, according to the World Health Organization criteria 6, 7

When polycythemia vera is suspected in a DVT patient, measurement of serum erythropoietin (EPO) is recommended, with low EPO having >90% specificity for polycythemia vera 8, 9
JAK2 mutation testing is also recommended, with JAK2 V617F (exon 14) present in >95% of polycythemia vera cases 8, 9

JAK2 V617F mutation testing is positive in >95 % of polycythemia vera (PV) cases, making it the primary molecular screen for suspected PV. World Health Organization (WHO) recommendation 10
If the JAK2 V617F test is negative, JAK2 exon 12 mutation testing should be performed, as it identifies an additional ~3 % of PV patients. WHO recommendation 10

Bone‑marrow biopsy in PV typically shows age‑appropriate hypercellularity with panmyelosis, increased megakaryocytes that form clusters and display pleomorphic morphology, and decreased iron stores. These histologic features confirm the diagnosis when molecular testing is equivocal. International Hematology Consensus 11

Patients classified as low‑risk (age < 60 years and no prior thrombosis) are managed with therapeutic phlebotomy to maintain hematocrit < 45 % and low‑dose aspirin. International Consensus on PV Management 11
High‑risk patients (age ≥ 60 years or history of thrombosis) require cytoreductive therapy (e.g., hydroxyurea, interferon‑α, or ruxolitinib) in addition to phlebotomy and aspirin. (Evidence not directly cited in the provided references)