Why Elevated Red Blood Cell Counts Disqualify Blood Donation: Clot Risk, Flow Impairment & Test Interference

Polycythemia (elevated hematocrit/hemoglobin/red cell mass) is a deferral criterion for blood donation due to physiological risks to both donor and recipient:

1. Hyperviscosity & Thrombosis Risk: Hct >55% (men) / >50% (women) exponentially increases blood viscosity. Donation-induced volume reduction + pre-existing hyperviscosity → stasis → venous/arterial thrombosis (DVT, PE, stroke, MI). Donor safety paramount.
2. Impaired Microcirculation: Excess RBCs impede capillary flow, causing tissue hypoxia paradoxically. Donation may acutely worsen oxygen delivery in vulnerable beds (cerebral, cardiac, renal).
3. Laboratory Interference: High Hct falsely elevates hemoglobin-based assays, alters plasma/serum ratios, affects coagulation studies, and can mask or mimic pathology in donor screening tests (e.g., infectious disease markers).

Underlying Causes Requiring Evaluation

• Primary: Polycythemia vera (JAK2 mutation).
• Secondary: Chronic hypoxia (COPD, sleep apnea, high altitude), EPO-secreting tumors, testosterone therapy, dehydration, smoking.

Deferred donors should be referred for medical workup. Therapeutic phlebotomy (not donation) is treatment for polycythemia vera.