What are the next steps for a 65-year-old asymptomatic patient with elevated hemoglobin, elevated hematocrit, and elevated red blood cell count?

Immediate Next Step: Test for JAK2V617F Mutation and Measure Serum Erythropoietin Level

In this 65-year-old asymptomatic patient with significant erythrocytosis (Hgb 17.2, Hct 52.8, RBC 6.03), you should immediately order JAK2V617F mutation testing and serum erythropoietin level, as these are the most relevant first tests to distinguish polycythemia vera from secondary causes 1.

Diagnostic Algorithm

Step 1: Confirm True Erythrocytosis

• Repeat complete blood count with differential and peripheral blood smear to confirm persistent elevation and assess other cell lines 2
• Look specifically for leukocytosis or thrombocytosis, which would strongly suggest a myeloproliferative neoplasm 3

Step 2: Initial Laboratory Testing

Order simultaneously:

• JAK2V617F mutation (most sensitive test for polycythemia vera)
• Serum erythropoietin level (low/normal in PV, elevated in secondary causes)
• C-reactive protein (to assess for inflammatory causes)
• Iron studies with ferritin (to exclude iron deficiency masking polycythemia)

Step 3: Targeted History and Physical Examination

Look for specific findings:

For Polycythemia Vera:

• Pruritus (especially after warm baths)
• Erythromelalgia (burning pain in hands/feet)
• Headaches or visual disturbances
• Splenomegaly on examination 3
• History of thrombosis

For Secondary Causes:

• Smoking history (chronic hypoxia)
• Sleep apnea symptoms
• Chronic lung disease
• Renal disease or masses
• Use of androgens, testosterone, or SGLT2 inhibitors 3
• Living at high altitude

Step 4: Interpretation and Further Testing

If JAK2V617F positive + low/normal erythropoietin:

• Proceed to bone marrow biopsy to confirm polycythemia vera diagnosis per WHO criteria 4
• PV diagnosis requires: Hgb >16.5 g/dL (men) or >16 g/dL (women), bone marrow hypercellularity with trilineage growth, and JAK2 mutation 5

If JAK2V617F negative + elevated erythropoietin:

• Investigate secondary causes systematically:
  • Arterial blood gas (hypoxemia from lung disease)
  • Renal ultrasound (renal tumors, cysts)
  • Sleep study if indicated
  • Chest imaging if pulmonary disease suspected

If JAK2V617F negative + low erythropoietin:

• Test for calreticulin (CALR) and MPL mutations 2
• Consider hereditary erythrocytosis (especially if young age or family history) 6
• Bone marrow biopsy may still be needed

Critical Pitfalls to Avoid

1. Don't assume relative polycythemia in asymptomatic patients: At age 65 with Hct 52.8%, this degree of elevation warrants full workup even without symptoms 7

2. Don't delay JAK2 testing: This is the single most important discriminating test and should not be deferred 1

3. Don't miss masked PV: Some patients have normal hemoglobin due to concurrent iron deficiency or blood loss but still have underlying PV 8. Check iron studies.

4. Don't forget thrombotic risk: Even asymptomatic patients with PV are at risk for thrombosis. At age 65, this patient would be high-risk if PV is confirmed 5

Risk Stratification if PV Confirmed

This patient's age (65 years) automatically places them in the high-risk category for thrombosis, which would mandate:

• Phlebotomy to maintain Hct strictly <45% 5
• Low-dose aspirin 5
• Cytoreductive therapy (hydroxyurea as first-line) 5

The evidence strongly supports that maintaining Hct <45% significantly reduces thrombotic events based on the CYTO-PV trial 5.