Introduction Polycythemia results from increased hemoglobin or hematocrit definition hemoglobin > 16.5 g/dL in men or > 16.0 g/dL in women hematocrit > 49% in men or > 48% in women types of polycythemia relative polycythemia normal red blood cell (RBC) mass with decreased plama volume absolute polycythemia increased RBC mass with normal plasma volume primary due to mutation in RBC progenitor cells resulting in proliferation secondary due to elevated erythropoietin (EPO) This topic focuses on secondary polycythemia Secondary Polycythemia Etiology Pathology Hypoxia Cardiopulmonary disease: cyanotic heart disease chronic pulmonary disease obstructive sleep apnea High altitude Carbon monoxide toxicity Smoking Combination of hypoxia, lung disease, carbon monoxide toxicity, and volume contraction Renal disease Kidneys sense decreased oxygen levels: reduced blood flow to the kidneys (renal artery stenosis) intrinsic renal disorder (renal cysts) (hydronephrosis) Renal transplantation Tumor Due to autonomous production of EPO Hepatocellular carcinoma Renal cell carcinoma Pheochromocytoma Hemangioblastoma Uterine leiomyomata Other Blood "doping" Self-injection of EPO Anabolic steroid use Studies Peripheral blood smear rule out other pathologies Serum EPO elevated suggests secondary polycythemia absent or low suggests primary polycythemia Complete blood count elevated hemoglobin and/or hematocrit Urinalysis and creatinine Electrolytes Liver function test Pulse oximetry Differential Primary polycythemia key distinguishing factors low or absent EPO consider JAK2 mutation testing Treatment Medical treat underlying condition Complications Thrombosis