The erythropoietin (EPO) test is a blood test used to measure the levels of EPO in the body. EPO is a hormone produced by the kidneys that stimulates the production of red blood cells in the bone marrow. The EPO test is commonly used to detect the use of performance-enhancing drugs in athletes, as synthetic EPO can increase the number of red blood cells and improve oxygen delivery to the muscles, thus enhancing performance. The test is also used to diagnose and monitor certain medical conditions, such as anemia, kidney disease, and cancer. High levels of EPO in the blood may indicate the presence of an underlying medical condition, while low levels may be a sign of kidney disease or anemia. However, the EPO test is not always reliable and may produce false-positive or false-negative results, so it is often used in combination with other diagnostic tests.