Polycythemia is a condition characterized by an increased number of red blood cells. There are two main types - primary polycythemia caused by internal problems producing red blood cells, and secondary polycythemia caused by other medical conditions stimulating red blood cell production. Primary polycythemia includes polycythemia vera related to a JAK2 gene mutation and primary familial polycythemia from an EPOR mutation. Secondary polycythemia can result from chronic hypoxia, tumors secreting erythropoietin, or living at high altitudes. Symptoms vary but can include easy bruising, bleeding, fatigue, and dizziness. Diagnosis involves medical history, exam, and blood