Erythropoietin is an essential hormone for red blood cell production. Without it, definitive erythropoiesis does not take place. Under hypoxic conditions, the kidney will produce and secrete erythropoietin to increase the production of red blood cells by targeting CFU-E, pro erythroblast and basophilic erythroblast subsets in the differentiation. Elevated erythropoietin levels are associated with the following: Iron-deficiency anemia. Anemia due to thalassemia. Hemolytic anemia. Anemia due to bone marrow suppression. Increased EPO level may be due to secondary polycythemia. This is an overproduction of red blood cells that occurs in response to an event such as low blood oxygen level. The condition may occur at high altitudes or, rarely, because of a tumor that releases EPO. They produce erythropoietin, a hormone that is vital for the production of red blood cells. The kidneys ensure that the make-up and volume of the fluids in the body is correct. They help control the chemical balance of the blood and regulate the body's level of sodium, potassium and calcium.