The clinical physiology of erythropoietin

From the foregoing data, it is clear that erythropoietin production is tightly regulated not only under normal circumstances but also during hypoxia, unless the hypoxia is extreme. Various disease states can have a negative impact on erythropoietin production, but while altering it quantitatively, they do not appear to abrogate basic fundamental control mechanisms. Rather, the threshold stimulus for either the recruitment of cells to produce erythropoietin or the effective production of erythropoietin is altered, usually in a predictable fashion. However, a reduction in erythropoietin production inevitably leads to a reduction in erythropoiesis. Nevertheless, assuming that the bone marrow remains responsive, administration of exogenous erythropoietin will increase the red blood cell mass. The immunoassay for serum erythropoietin therefore provides a means for identifying those situations in which erythropoietin therapy should be effective, but the assay must be used critically, bearing in mind the physiology of the hormone and the threshold concept of erythropoietin production (Table 3).