Serum immunoreactive erythropoietin in health and disease.

Erythropoietin, the glycoprotein which regulates erythropoiesis is unique amongst the hematopoietic growth factors since it is the only one which behaves like a hormone. Produced primarily in the kidneys in adults, erythropoietin interacts with erythroid precursors in the marrow to increase red cell production. Because erythropoietin behaves like a hormone, measurements of erythropoietin in the serum have proved useful in determining when production of this hormone is inadequate. Tissue hypoxia is the only physiologic stimulus for erythropoietin production and thus, with anemia, serum erythropoietin levels should be increased. Assuming normal marrow function and adequate nutrient supplies, when anemia is associated with a low serum erythropoietin level, it can be concluded that the anemia is in part due to erythropoietin lack and should be correctable by administration of erythropoietin. As a corollary, a high serum erythropoietin level (greater than 500 mU/ml) in the presence of anemia suggests that there is end organ failure, and erythropoietin therapy is not likely to be useful.