What is the next step in management for a patient with elevated hemoglobin (Hgb), hematocrit (Hct), red blood cell count (RBC), white blood cell count (WBC), and neutrophil count?

Management of Elevated Blood Counts on Fasting Labs

Repeat the CBC in a non-fasting state and continue daily aspirin while evaluating for polycythemia vera and other myeloproliferative neoplasms, as fasting can cause hemoconcentration that falsely elevates all cell lines.

Immediate Next Steps

Confirm True Elevation vs. Artifact

• Order non-fasting CBC with differential to distinguish true polycythemia from relative polycythemia caused by dehydration or hemoconcentration during fasting 1, 2
• Fasting can affect blood cell parameters through volume shifts, making it essential to verify results under normal hydration conditions 3
• Continue daily aspirin as initiated, which is appropriate for suspected myeloproliferative disorders to reduce thrombotic risk 4

Evaluate for Polycythemia Vera (PV)

If the non-fasting CBC confirms persistent elevations across multiple cell lines (hemoglobin, hematocrit, RBC, WBC, neutrophils), this pattern strongly suggests a myeloproliferative neoplasm, particularly polycythemia vera 4, 5:

Essential workup includes:

• JAK2 V617F mutation testing - present in >95% of PV cases 4
• Serum erythropoietin level - typically low or low-normal in PV 4
• Peripheral blood smear to assess cell morphology and rule out other causes 2, 5
• Bone marrow biopsy with cytogenetic analysis if diagnosis remains unclear after initial testing 4

Rule Out Secondary Causes

For elevated hemoglobin/hematocrit:

• Assess for chronic hypoxia (pulse oximetry, arterial blood gas if indicated) 1
• Screen for sleep apnea, chronic lung disease, or cardiac right-to-left shunts 5
• Check for renal pathology (renal ultrasound, creatinine) as renal tumors can produce erythropoietin 1

For elevated WBC/neutrophils:

• Rule out infection with appropriate cultures if clinically indicated 4, 6
• Review medications that can cause leukocytosis (corticosteroids, growth factors) 4, 6
• Assess for inflammatory conditions (ESR, CRP) 6

Common Pitfalls to Avoid

• Do not assume dehydration alone - while fasting causes hemoconcentration, simultaneous elevation of all three cell lines (RBC, WBC, platelets) is more concerning for a primary bone marrow disorder 2, 5
• Do not delay aspirin - thrombotic complications are a major cause of morbidity in myeloproliferative disorders, and aspirin should be continued unless contraindicated 4
• Do not order extensive workup before confirming persistent elevation - verify with non-fasting labs first to avoid unnecessary testing 3

Monitoring Strategy

If non-fasting CBC normalizes:

• Likely represented relative polycythemia from dehydration 1
• Continue aspirin only if other cardiovascular indications exist
• No further hematologic workup needed unless symptoms develop

If non-fasting CBC remains elevated:

• Proceed urgently with JAK2 mutation testing and erythropoietin level 4
• Maintain aspirin 81-100 mg daily 4
• Refer to hematology for definitive diagnosis and management 4, 5
• Monitor CBC weekly until diagnosis established 4

The key distinction is that true polycythemia vera presents with persistent pan-elevation of blood counts independent of hydration status, while fasting-related changes resolve with rehydration 1, 3.