Erythropoietin is the major hormone regulator of erythrocyte production promoting the survival, as well as the differentiation and maturation, of erythroid progenitor cells. In addition to these well-characterized effects, it appears that an erythropoietin-responsive non-erythroid mechanism also mediates the selective destruction of young circulating erythrocytes (neocytes) when red cell mass becomes excessive – a process termed ‘neocytolysis’. Endothelial cells appear to respond to a rapid decrease in circulating levels of erythropoietin by secreting cytokines (including TGF-α), which signal reticuloendothelial phagocytes to destroy neocytes. The result is a more rapid decrease in red cell mass than can be explained by natural erythrocyte senescence alone. The current pharmacologic approach to treatment of anaemia in chronic kidney disease may cause neocytolysis and could keep therapy from reaching its full potential. Understanding neocytolysis and its relationship to fluctuating serum erythropoietin levels might help to better understand optimal treatment with erythropoietic agents.

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