When should a patient with polycythemia vera (PV) be referred to a hematologist for further evaluation and management?

When to Refer a Patient with Polycythemia Vera to a Hematologist

All patients with suspected or confirmed polycythemia vera should be referred to a hematologist for initial diagnosis confirmation, risk stratification, and treatment planning, with ongoing co-management between hematology and primary care thereafter. 1, 2

Immediate Referral Situations

Refer urgently when any of the following are present:

• Hemoglobin ≥18.5 g/dL in men or ≥16.5 g/dL in women with suspected PV 2, 3
• Unusual thrombosis locations, particularly splanchnic vein thrombosis (Budd-Chiari syndrome, portal vein thrombosis, mesenteric vein thrombosis) 1, 2, 4
• Aquagenic pruritus (intense itching triggered by water contact without skin lesions) suggesting underlying myeloproliferative neoplasm 1, 2
• Erythromelalgia (painful burning sensation of feet/hands with erythema and warmth) 1, 2
• Sustained hemoglobin increase ≥2 g/dL from baseline, even if within normal reference ranges 2, 3
• Extreme thrombocytosis (platelet count ≥1,000 × 10⁹/L) due to paradoxical bleeding risk from acquired von Willebrand disease 3, 4

Diagnostic Confirmation Requiring Hematology Expertise

Bone marrow examination is essential before initiating cytoreductive therapy and requires hematologist interpretation for characteristic findings including hypercellularity, increased megakaryocytes with cluster formation, giant megakaryocytes with pleomorphic morphology, and mild reticulin fibrosis 1, 2, 3

JAK2 mutation testing interpretation requires hematology input, particularly when JAK2V617F is negative and JAK2 exon 12 testing or calreticulin mutation screening is needed 1, 2

Treatment Decisions Requiring Hematology Consultation

High-risk patients (age ≥60 years or prior thrombosis history) require cytoreductive therapy decisions that mandate hematologist involvement 1, 4, 5

Cytoreductive therapy initiation with hydroxyurea, interferon-α, busulfan, or ruxolitinib requires hematologist prescription and monitoring 1, 6, 4

Women of childbearing age require specialized consultation for interferon-α therapy planning, as this is preferred over potentially teratogenic alternatives like hydroxyurea or busulfan 1, 6

Intractable pruritus not responding to conventional antihistamines requires hematologist evaluation for interferon-α or ruxolitinib therapy 1, 6

Ongoing Monitoring Requiring Hematology Input

Hydroxyurea resistance or intolerance (occurring in approximately 25% of patients) requires hematologist assessment for alternative cytoreductive agents 7, 4

Disease transformation surveillance for myelofibrosis (10-year risk ~10%) or acute leukemia (10-year risk ~5%) requires periodic hematology evaluation 1, 6, 4

Leukocytosis >15 × 10⁹/L indicates inferior survival and increased thrombotic risk requiring hematologist risk reassessment 3

Common Pitfalls to Avoid

Do not delay referral while attempting to rule out secondary causes of polycythemia in primary care if JAK2 mutation is positive or bone marrow findings are characteristic 1, 2

Do not manage cytoreductive therapy without hematology involvement, as drug selection, dosing, and monitoring for complications (including leukemogenicity concerns) require specialized expertise 1, 6

Do not assume low-risk disease can be managed indefinitely without hematology follow-up, as risk stratification changes with age and thrombotic events 1, 4, 5