Erythropoietin.

Maintenance of the red cell volume is a fundamental aspect of ensuring oxygen supply to the tissues. The balance between the very dynamic processes of erythropoiesis and erythrocyte loss is precarious and yet normal individuals experience a remarkably constant haematocrit. This is achieved by a very elegant and sensitive homeostatic mechanism which links tissue oxygen delivery to red cell production. The glycoprotein hormone erythropoietin (EPO) is the principle controller of this process. It is now clear that even minor underproduction of EPO will result in anaemia. The most widespread example of this is the anaemia of end-stage renal failure. The pharmacological use of recombinant human EPO (rHuEPO) in this setting is now well established and has had a dramatic impact on the quality of life of patients with renal disease. With the more widespread use of EPO in other clinical conditions and the advent of novel therapeutic approaches, this is an opportune moment to review the physiology and patho-physiology of this fascinating and essential hormone.