polycythemia

Polycythemia is a condition characterized by an increased red blood cell mass, usually documented as elevated hemoglobin or hematocrit. It can be absolute, due to increased red cell production, or relative, due to reduced plasma volume. The term polycythemia vera refers to a primary myeloproliferative neoplasm causing sustained erythrocytosis, often with leukocytosis and thrombocytosis.

Absolute polycythemia is divided into primary and secondary forms. Primary polycythemia, or polycythemia vera, results from clonal proliferation of erythroid cells, most commonly associated with a JAK2 V617F mutation. Secondary polycythemia arises from increased erythropoietin production in response to hypoxia (lung disease, high altitude, sleep apnea, smoking) or from EPO-secreting tumors and rarely other conditions. Relative polycythemia is due to dehydration or plasma volume loss.

Symptoms and signs include headache, dizziness, fatigue, ruddy complexion, and sometimes pruritus after warm water (aquagenic pruritus) in polycythemia vera. Increased blood viscosity raises risk of thrombosis and bleeding. Splenomegaly can occur in PV. The clinical picture varies with the underlying cause and the degree of erythrocytosis.

Diagnosis rests on blood tests showing elevated hemoglobin and hematocrit, with confirmation of absolute erythrocytosis by erythrocyte mass studies if needed. JAK2 testing supports PV; other mutations (MPL, CALR) may be present. Erythropoietin level helps differentiate primary from secondary forms. Evaluation for hypoxia, smoking, lung disease, altitude, tumors, and hydration status is essential.

Treatment aims to reduce thrombotic risk and control symptoms. In polycythemia vera, therapeutic phlebotomy to keep hematocrit under 45% (men) or 42% (women), plus low-dose aspirin, is standard; cytoreductive therapy (hydroxyurea or ruxolitinib) is used for high-risk or resistant cases. Secondary polycythemia management focuses on treating hypoxia or the underlying cause. Prognosis depends on the underlying form and thrombotic risk, with regular monitoring.