erythropoietin

erythropoietin A hormone that is produced by the kidney and promotes the formation of red blood cells in the bone marrow. Abbreviated EPO. Human EPO is a glycoprotein (a protein with an attached sugar) that has a molecular weight of 34,000. The kidney cells that make EPO are specialized and are sensitive to low oxygen levels in the blood that comes into the kidney. These cells release EPO when the blood oxygen level is low. EPO stimulates the bone marrow to produce more red blood cells, which in turn increases the oxygen-carrying capacity of the blood. EPO is produced not only in the kidney but also, to a lesser extent, in the liver. The amount of EPO in the blood can indicate bone marrow disorders or kidney disease. Normal levels of EPO are 0 to 19 milliunits per milliliter (mU/ml). Elevated levels can be seen in polycythemia rubra vera, a disorder characterized by an excess of red blood cells. Lower-than-normal values of EPO are seen in chronic renal failure. Using recombinant DNA technology, EPO has been synthetically produced for use in persons with anemia due to kidney failure and other conditions. It has been misused as a performance-enhancing drug in endurance athletes, reportedly including cyclists, long-distance runners, speed skaters, and cross-country skiers. As such, EPO is thought to be especially dangerous, perhaps because dehydration can further increase the thickness of the blood, increasing the risk for heart attacks and strokes. See also EPO test.