What are the necessary tests and evaluations to diagnose and manage a patient with suspected polycythemia vera?

Diagnostic Workup for Suspected Polycythemia Vera

Begin with serum erythropoietin (EPO) level measurement followed by JAK2 mutation testing and bone marrow examination to establish the diagnosis of polycythemia vera. 1

Initial Laboratory Assessment

Confirm true erythrocytosis with repeat hemoglobin/hematocrit measurements before proceeding with extensive workup. 1 The diagnostic threshold is hemoglobin >16.5 g/dL in men or >16.0 g/dL in women, though a sustained increase of ≥2 g/dL from baseline warrants investigation even within normal reference ranges. 2, 1

Essential First-Line Tests

• Serum EPO level - This is the critical first test that guides the entire diagnostic algorithm. 3, 1

  • EPO <3.3 IU/L (below normal range) has 97% specificity and 97.8% positive predictive value for PV 4
  • EPO <1.4 IU/L provides direct diagnosis of PV in 65.6% of untreated cases 4
  • Critical caveat: Normal EPO levels occur in 20-30% of PV patients, so normal EPO does NOT exclude PV (sensitivity only 64-70%) 1, 5
  • Elevated EPO (>13.7 IU/L) strongly suggests secondary polycythemia and triggers evaluation for hypoxia-driven or tumor-related causes 4, 1

• JAK2 mutation testing - Order immediately alongside EPO measurement. 1, 2

  • JAK2V617F mutation is present in >95% of PV patients 2, 6
  • This test is essential when EPO is low or normal 7
  • Positive JAK2 with low/normal EPO essentially confirms PV diagnosis 1

• Complete blood count with differential - Assess for accompanying thrombocytosis (53% of cases) and leukocytosis (49% of cases). 2, 7

• Mean corpuscular hemoglobin concentration (MCHC) - Low MCHC (<32%) indicates iron deficiency that can mask true erythrocytosis; if present, order serum ferritin, iron studies, and transferrin saturation. 1, 8

Bone Marrow Examination

Proceed with bone marrow biopsy when:

• EPO is low or normal AND JAK2 is positive (to confirm diagnosis) 3, 1
• EPO is normal but clinical suspicion remains high (mandatory for diagnostic confirmation) 5
• The diagnosis remains equivocal after initial testing 3

Key Bone Marrow Findings in PV

• Hypercellularity with trilineage proliferation 3, 1
• Increased megakaryocytes with cluster formation and pleomorphic morphology 3, 1
• Giant megakaryocytes 3, 1
• Decreased bone marrow iron stores 3, 8
• Mild reticulin fibrosis (present in 12% at diagnosis) 3

Cytogenetic studies have limited diagnostic value (abnormalities in only 13-18% at diagnosis) but should be performed as part of the bone marrow workup. 3, 1

Clinical Features That Strengthen Diagnosis

Look specifically for these PV-associated manifestations:

• Aquagenic pruritus (33% of patients) - itching triggered by water contact 2, 1
• Erythromelalgia (5.3% of patients) - burning pain and redness in extremities 2, 1
• Unusual thrombosis - particularly Budd-Chiari syndrome or other splanchnic vein thrombosis 1, 2
• Splenomegaly (36% of patients) with abdominal discomfort 2
• Transient visual changes (14% of patients) 2

Specialized Testing for Equivocal Cases (<10% of patients)

When diagnosis remains uncertain after EPO, JAK2, and bone marrow examination:

• Bone marrow immunohistochemistry for c-mpl (thrombopoietin receptor) - markedly decreased expression supports PV diagnosis 3, 1
• Neutrophil PRV-1 expression assay - high expression favors PV over secondary polycythemia, though limited availability 3, 1
• Spontaneous erythroid colony assay - rarely used due to limited availability and need for expertise 3, 1

Excluding Secondary Polycythemia

When EPO is elevated or normal, systematically evaluate for secondary causes:

Hypoxia-Driven Causes

• Arterial blood gas or pulse oximetry - assess for hypoxemia 7
• Detailed smoking history - smoker's polycythemia from chronic carbon monoxide exposure is the most common secondary cause and resolves with cessation 7, 1
• Sleep study - if sleep apnea suspected 7
• Chest X-ray - evaluate for chronic lung disease 7

Hypoxia-Independent Causes

• Abdominal ultrasound or CT - screen for EPO-producing tumors (renal cell carcinoma, hepatocellular carcinoma, uterine leiomyomas, pheochromocytoma) 7, 1
• Medication review - check for exogenous erythropoietin or testosterone use 7
• Renal function tests - assess for post-renal transplant erythrocytosis in transplant recipients 7

Critical Diagnostic Pitfalls to Avoid

• Do not assume normal EPO excludes PV - 20-30% of PV patients have normal EPO at presentation; proceed with JAK2 testing regardless. 5, 1

• Do not miss iron deficiency - low MCHC can mask true erythrocytosis by falsely normalizing hematocrit while red cell mass remains elevated. 1, 8

• Do not rely on traditional markers alone - splenomegaly, elevated leukocyte alkaline phosphatase, and increased vitamin B12 levels lack sufficient sensitivity and specificity for diagnosis. 1

• Do not perform unnecessary red cell mass measurements - modern JAK2 testing and EPO levels have largely replaced the need for Cr-51 RCM studies except in truly equivocal cases. 1, 5

• Exclude dehydration first - this is the most common cause of falsely elevated hematocrit; assess for plasma volume depletion before extensive workup. 7, 8

• Beware of "normalized" EPO in chronic hypoxia - in long-standing hypoxic states, EPO may initially be elevated but return to normal range once hemoglobin stabilizes at a compensatory higher level, potentially mimicking PV. 1, 7

Diagnostic Algorithm Summary

1. Confirm elevated hemoglobin/hematocrit with repeat measurements
2. Order EPO level + JAK2 mutation testing simultaneously
3. If EPO low (<3.3 IU/L) + JAK2 positive → Proceed to bone marrow biopsy to confirm PV
4. If EPO normal + JAK2 positive → Bone marrow biopsy mandatory for confirmation 5
5. If EPO elevated (>13.7 IU/L) → Systematically evaluate for secondary polycythemia causes 4
6. Bone marrow findings characteristic for PV + low/normal EPO + JAK2 positive = Confirmed PV diagnosis 3, 1