When to refer a patient with suspected polycythemia vera to a hematologist?

When to Refer a Patient with Suspected Polycythemia Vera to a Hematologist

Refer immediately to hematology if JAK2 mutation testing is positive, or if the patient has hemoglobin >20 g/dL with symptoms of hyperviscosity, or if diagnosis remains unclear after initial workup. 1

Immediate Referral Criteria

Refer urgently to a hematologist in the following situations:

• Positive JAK2 mutation (exon 14 V617F or exon 12) – This confirms a myeloproliferative neoplasm requiring specialist management 1
• Hemoglobin >20 g/dL and hematocrit >65% with symptoms of hyperviscosity (headache, visual disturbances, dizziness, erythromelalgia) 1
• Unexplained splenomegaly in the context of erythrocytosis 1
• Thrombosis in unusual sites (splanchnic, cerebral venous sinus) with elevated hemoglobin/hematocrit 1

Criteria Warranting Hematology Evaluation

Consider referral when the following features are present:

• Sustained erythrocytosis with hemoglobin >18.5 g/dL in men or >16.5 g/dL in women on repeat testing 1
• Hematocrit >55% in men or >49.5% in women confirmed on multiple occasions 1
• Progressive rise in hemoglobin ≥2 g/dL from baseline even if within normal reference ranges 2
• Associated myeloproliferative features: thrombocytosis, leukocytosis, aquagenic pruritus, or erythromelalgia 1

Initial Workup Before Referral

Primary care should complete the following evaluation before or concurrent with referral:

• JAK2 V617F mutation testing – Present in >95% of PV cases and essential for diagnosis 1, 3
• Complete blood count with differential – Assess for thrombocytosis and leukocytosis 1
• Serum erythropoietin level – Low EPO has >90% specificity for PV 2
• Iron studies (ferritin, transferrin saturation) – Iron deficiency can mask true erythrocytosis 2, 1
• Peripheral blood smear review – Evaluate red cell morphology 1

When Referral Can Be Deferred

Hematology referral may not be immediately necessary if:

• Secondary causes are clearly identified and treatable: obstructive sleep apnea, COPD, smoking, testosterone therapy 1
• Borderline elevations (hemoglobin 16-18 g/dL in men, 15-16 g/dL in women) with negative JAK2 mutation and identifiable secondary cause 1
• Relative polycythemia due to dehydration or diuretic use that resolves with hydration 1

However, if secondary causes are treated and erythrocytosis persists, refer to hematology for further evaluation 1

Critical Diagnostic Pitfalls

Avoid these common errors that delay appropriate referral:

• Do not dismiss erythrocytosis based on a single measurement – Repeat testing is essential to confirm persistent elevation 1
• Do not overlook iron deficiency coexisting with erythrocytosis – Low MCHC (<32%) suggests iron deficiency that can mask the true severity of polycythemia 2
• Do not assume dehydration without confirmation – While dehydration is the most common cause of falsely elevated hematocrit, true PV must be excluded 2
• Do not delay JAK2 testing – This is the single most important diagnostic test and should be ordered promptly when PV is suspected 1, 4

Special Populations Requiring Lower Threshold for Referral

Refer more readily in these situations:

• Young patients (<40 years) with unexplained erythrocytosis – Higher lifetime risk of complications 5
• Women of childbearing age – Pregnancy management in PV requires specialist input 6, 7
• Patients with prior thrombotic events – High-risk status requiring cytoreductive therapy 5
• Atypical presentations (recurrent eye redness, unexplained dizziness) that may represent microvascular complications 4

Urgency of Referral Based on Clinical Context

Emergent referral (same day):

• Symptomatic hyperviscosity with hemoglobin >20 g/dL 1
• Acute thrombotic event with erythrocytosis 1

Urgent referral (within 1-2 weeks):

• Positive JAK2 mutation 1
• Hemoglobin >18.5 g/dL (men) or >16.5 g/dL (women) with negative secondary workup 1

Routine referral (within 4-6 weeks):

• Persistent borderline erythrocytosis after treating secondary causes 1
• Unclear diagnosis after initial workup 1