Polycythemia

An abnormal increase in the concentration of red blood cells (or hemoglobin). Possible causes are clonal/myeloproliferative polycythemia vera, hypoxia (high altitudes, chronic smoking, COPD, sleep apnea), secondary to increased erythropoietin (kidney disease, tumor), medications (steroids, testosterone), and false positive apparent polycythemia seen in patients with dehydration (increased concentration due to intravasal fluid reduction).