An erythropoietin assay using hypertransfused rats and radioiron utilization has been evaluated in regard to modifying factors and its variability. It is proposed that the dose-response relationship may be regarded as an adsorptive process which suggests new investigative approaches in terms of hormone binding sites and erythropoietin inhibition.

Elevated levels of erythropoietin were found in 14 of 16 patients with refractory anemia indicating a basic defect in the response of the erythroid marrow. The two exceptions are of great theoretical interest, but insufficient information limits further conclusions. Patients with hypoxic polycythemia demonstrated increased levels only when their compensatory equilibrium had been modified by phlebotomy. Seven patients with polycythemia vera had erythropoietin levels within the normal range whether or not therapy had modified their red cell mass. This is further evidence that polycythemia vera is a proliferative disorder usurping the normal regulation. The clinical use of erythropoietin assay may provide the most information when correlated with alterations of oxygen-carrying capacity as a functional test of the patient’s erythropoietic regulatory mechanism.

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