Polycythemias

Polycythemias are a group of disorders characterized by an increased red blood cell mass, which raises hemoglobin concentration and hematocrit. They can be classified as primary polycythemias, secondary polycythemias, and relative polycythemia. Diagnosis relies on blood counts and may include measurements of erythropoietin, assessment of oxygenation status, and, when appropriate, molecular testing for mutations such as JAK2.

Primary polycythemia, most often polycythemia vera, is a myeloproliferative neoplasm with clonal erythrocyte expansion. It is commonly associated with a JAK2 mutation (V617F in the majority of cases). Patients may have headaches, dizziness, a ruddy complexion, splenomegaly, and pruritus. Thrombosis is the major complication. Treatment aims to reduce red cell mass and thrombotic risk: phlebotomy to achieve a hematocrit around 45%, low-dose aspirin for most patients, and cytoreductive therapy (such as hydroxyurea) for higher risk or inadequately controlled disease. Interferon is an option for younger patients or those who prefer to avoid hydroxyurea.

Secondary polycythemia results from increased erythropoietin production or activity in response to chronic hypoxia or ectopic EPO production by tumors. Causes include chronic lung disease, high altitude, sleep apnea, smoking, renal cell carcinoma, and hepatocellular carcinoma. Management focuses on treating the underlying cause; oxygen therapy for hypoxia, smoking cessation, management of sleep apnea, and, when appropriate, treatment of the tumor. Phlebotomy may be used for symptomatic relief but requires careful monitoring.

Relative polycythemia, or pseudo-polycythemia, occurs when plasma volume is reduced, causing apparent RBC concentration despite a normal red cell mass. Treatment targets fluid balance and underlying causes.