What tests are required to diagnose and manage a patient with suspected polycythemia vera or other myeloproliferative neoplasms?

Diagnostic Tests Required for Polycythemia Vera and Myeloproliferative Neoplasms

The diagnosis of polycythemia vera (PV) and other myeloproliferative neoplasms (MPNs) requires testing for JAK2V617F mutation as the primary molecular marker, along with complete blood count, serum erythropoietin level, and bone marrow examination with cytogenetic studies. 1, 2

Initial Laboratory Tests

• Complete blood count (CBC) with differential to assess for erythrocytosis (hemoglobin >16.5 g/dL in men or >16.0 g/dL in women), thrombocytosis, and leukocytosis 2
• Serum erythropoietin level - typically low in PV, which helps distinguish it from secondary causes of polycythemia 1
• Peripheral blood smear examination to evaluate red cell morphology and assess for other abnormalities 1
• Comprehensive metabolic panel including serum creatinine, calcium, and albumin 1

Molecular and Genetic Testing

• JAK2V617F mutation testing - present in >95% of PV cases and is a critical diagnostic marker 1, 2, 3
• If JAK2V617F is negative but PV is still suspected, test for JAK2 exon 12 mutations 3
• In JAK2-negative patients with suspected MPNs, calreticulin (CALR) mutation screening should be performed 1
• If both JAK2 and CALR are negative, consider MPL mutation testing 1

Bone Marrow Evaluation

• Bone marrow aspiration and biopsy with cytogenetic studies 1
• Histological examination to assess for characteristic features:
  • Hypercellularity
  • Increased megakaryocytes with cluster formation
  • Presence of giant megakaryocytes and pleomorphism
  • Mild reticulin fibrosis (in some cases)
  • Decreased bone marrow iron stores 1

Additional Specialized Tests

• In equivocal cases, consider specialized tests such as:
  • Bone marrow immunohistochemistry for thrombopoietin receptor (c-mpl) expression 1
  • Peripheral blood neutrophil assay for PRV-1 expression 1
  • Spontaneous (endogenous) erythroid colony assays (though limited availability) 1

Thrombophilia Screening

• For patients with MPNs who present with splanchnic vein thrombosis (SVT), conduct thrombophilia screening including:
  • Protein S, protein C, and antithrombin levels
  • Factor V Leiden mutation
  • Prothrombin G20210A gene variant
  • Anti-phospholipid antibodies (repeat after 12 weeks if positive) 1

Imaging Studies

• Consider imaging studies if there is suspicion of extramedullary hematopoiesis or complications:
  • Abdominal ultrasound to assess spleen size 4
  • Doppler ultrasound, MRI, or CT if splanchnic vein thrombosis is suspected 1

Diagnostic Algorithm

1. Start with CBC and serum erythropoietin level when PV is suspected 1
2. If serum erythropoietin is low or normal and erythrocytosis is present, proceed with JAK2V617F mutation testing 1
3. If JAK2V617F is positive, proceed with bone marrow examination to confirm diagnosis 1
4. If JAK2V617F is negative but clinical suspicion remains high, test for JAK2 exon 12 mutations 3
5. In cases with normal or borderline hematocrit but other MPN features (thrombocytosis, leukocytosis, splenomegaly), consider bone marrow examination and expanded molecular testing 5

Common Pitfalls and Caveats

• Plasma volume expansion in PV can mask true erythrocytosis, particularly in women presenting with isolated thrombocytosis 5
• A normal hematocrit does not exclude PV, especially in the presence of splenomegaly or other cytopenias 5
• Testing for JAK2V617F should be performed even in patients with normal peripheral blood cell counts if MPN is suspected 1
• Bone marrow examination is essential for distinguishing between different MPNs, particularly when peripheral blood findings are equivocal 1
• Secondary causes of erythrocytosis (smoking, sleep apnea, etc.) should be excluded, though they can coexist with PV 2

Following this comprehensive diagnostic approach will help establish an accurate diagnosis of PV or other MPNs, which is crucial for appropriate management and prevention of complications such as thrombosis, hemorrhage, and disease transformation 4.