High Red Blood Cell Count (Polycythemia): Causes and Risks

Polycythemia/erythrocytosis = RBC count above normal. Causes:

Increased Production (Primary or Secondary)

• Polycythemia vera: JAK2-mutated myeloproliferative neoplasm (blood cancer).
• Chronic hypoxia: COPD, sleep apnea, high altitude, congenital heart disease → EPO-driven.
• Renal lesions: Cysts, tumors, transplant kidney → excess EPO.
• EPO doping or testosterone therapy.

Decreased Destruction / Relative Polycythemia

• Splenectomy: Loss of RBC sequestration.
• Dehydration/GI loss: Hemoconcentration (relative polycythemia).
• Iron deficiency: Paradoxically can elevate RBC count (microcytosis).

Risks

• Hyperviscosity → thrombosis (stroke, MI, DVT, PE), sluggish flow.
• Hypertension, headache, dizziness, ruddy complexion, pruritus (after warm shower).
• Bleeding paradox (platelet dysfunction from hyperviscosity).

Evaluation: JAK2 testing, EPO level, O₂ saturation, abdominal imaging, bone marrow biopsy if indicated. Treatment: phlebotomy, hydroxyurea, aspirin, treat underlying cause.