Erythropoietin (EPO) is a hormone
that stimulates the formation and growth of red blood cells
. It is produced mainly by the kidney
. It is secreted in the case of low concentration of arterial oxygen, decreased red blood
cells, or an increase in oxygen demand. In certain kidney diseases
, as in renal tumors
, EPO is secreted in excess and generates an excessive concentration of red blood cells which can be responsible for thrombosis because the blood is made more viscous. In cases of renal failure, erythropoietin is impaired and can be replaced by synthetic erythropoietin. Note that the EPO has sometimes been used as a doping agent to increase the oxygen supply to the muscles
and improve athletic performance.