What is the appropriate workup for polycythemia in a patient who is not on testosterone therapy?

Workup for Polycythemia (Not on Testosterone Therapy)

Begin with JAK2 mutation testing and serum erythropoietin level as your initial diagnostic tests after confirming true polycythemia with hemoglobin/hematocrit thresholds, then proceed to bone marrow biopsy if JAK2 is positive or if clinical suspicion for myeloproliferative neoplasm remains high 1.

Initial Laboratory Confirmation

First, confirm true polycythemia exists:

• Men: Hemoglobin >16.5 g/dL or Hematocrit >49%
• Women: Hemoglobin >16.0 g/dL or Hematocrit >48%

Check complete blood count looking specifically for:

• Thrombocytosis (platelets >400 × 10⁹/L) - present in 53% of PV cases
• Leukocytosis (WBC >12 × 10⁹/L) - present in 49% of PV cases

If polycythemia is isolated (no thrombocytosis or leukocytosis), prioritize searching for secondary causes first 2. If accompanied by thrombocytosis or leukocytosis, immediately test for JAK2 mutations as polycythemia vera becomes more likely 2, 3.

Core Diagnostic Tests

1. JAK2 Mutation Testing

• JAK2 V617F mutation is present in >95% of polycythemia vera cases 1, 3
• This single test distinguishes primary from secondary polycythemia, as JAK2 mutations are absent in secondary causes 1
• If negative, consider JAK2 exon 12 mutations (rare PV variant) 1

2. Serum Erythropoietin Level

• Low or low-normal EPO suggests polycythemia vera 1
• Elevated EPO points toward secondary erythrocytosis 2
• This helps differentiate autonomous RBC production (PV) from reactive processes

3. Bone Marrow Biopsy

Perform if:

• JAK2 mutation is positive (to confirm diagnosis and establish baseline) 4
• Clinical features suggest myeloproliferative neoplasm even if JAK2 negative
• Before initiating cytoreductive therapy 4

Look for: Panmyelosis with prominent erythroid and megakaryocytic proliferation 1

Secondary Causes to Exclude

Systematically evaluate for:

Hypoxia-related:

• Pulse oximetry and arterial blood gas (looking for oxygen saturation <92%) 1
• Chest X-ray for chronic lung disease 5
• Sleep study if obstructive sleep apnea suspected 3
• High altitude residence history

Medication-induced:

• SGLT2 inhibitors 2
• Anabolic steroids or androgens (you've already excluded testosterone) 6
• Erythropoietin-stimulating agents

Tumor-related:

• Renal ultrasound or CT abdomen (renal cell carcinoma, hepatocellular carcinoma) 1
• Consider other EPO-secreting tumors if clinical suspicion exists

Other causes:

• Smoking history (carboxyhemoglobin levels if heavy smoker) 3
• Assess for chronic dehydration/relative polycythemia 2

Diagnostic Algorithm Based on Results

If JAK2 positive + low EPO + bone marrow shows panmyelosis:

• Diagnosis = Polycythemia Vera 1
• Proceed to risk stratification and treatment per NCCN guidelines 4

If JAK2 negative + elevated EPO:

• Diagnosis = Secondary Polycythemia 2
• Focus workup on identifying and treating underlying cause
• Consider hereditary erythrocytosis testing if no secondary cause found 2

If JAK2 negative + low EPO:

• Consider rare JAK2 exon 12 mutations 1
• Evaluate for hereditary causes (VHL gene, EPOR mutations, high oxygen-affinity hemoglobin variants) 2

Physical Examination Findings to Assess

Look specifically for:

• Splenomegaly (present in 36% of PV, suggests myeloproliferative disorder) 4, 3
• Plethora (ruddy complexion)
• Pruritus after warm bath (33% of PV patients) 3
• Erythromelalgia (burning pain in extremities, 5.3% of cases) 3
• Signs of prior thrombosis (16% arterial, 7% venous at diagnosis) 3

Critical Pitfalls to Avoid

• Don't assume PV without JAK2 testing - most polycythemia in general practice is relative or secondary 2
• Don't skip bone marrow biopsy in JAK2-positive patients - needed before cytoreductive therapy and to rule out progression 4
• Don't forget splanchnic vein thrombosis - PV can present with unusual venous thromboses 3
• Don't overlook secondary causes even with mild JAK2 positivity - can coexist rarely 2

The strength of this approach lies in the 2007 WHO revised criteria 1, which fundamentally changed polycythemia diagnosis by incorporating JAK2 mutations as a major criterion, eliminating the need for many previously required tests. The NCCN 2017 guidelines 4 provide the treatment framework once diagnosis is established.