Overview: Erythropoiesis, anemia, and the impact of erythropoietin

The final stages of maturation of erythroid cells into mature red blood cells are regulated by the growth factor erythropoietin. Circulating levels of erythropoietin are remarkably consistent across the range of normal hemoglobin levels; levels increase markedly as hemoglobin declines below 12 g/dL in a manner suggesting that mechanisms in addition to the level of tissue oxygen are important in regulating increases in erythropoietin production and erythropoiesis. The erythropoietin receptor is found on a number of cell types in addition to erythroid progenitor cells, suggesting that erythropoietin may have specific biologic effects on other tissues, still to be carefully discerned. Clinical trials have demonstrated the effectiveness of recombinant human erythropoietin (epoetin alfa) in increasing hemoglobin level in iatrogenic and disease-related anemias. This increase has been associated with improving fatigue symptoms and enhancing overall quality of life. Questions remain, however, regarding the optimal increases in hemoglobin to be achieved in anemic patients with such therapy and whether optimal levels might vary in different patient groups.