The erythropoietin-hematocrit relationship in normal and polycythemic man: implications of marrow regulation.

The relationship between erythropoietin excretion and change in hematocrit has been determined in normal and polycythemic subjects. Erythropoietin was measured by a method involving the assay of urinary concentrates in polycythemic protein-depleted mice. Basal erythropoietin excretion in normal subjects ranged from 2.8 to 7.5 Standard B units per day. Studies in subjects made anemic by bleeding demonstrated an inverse relationship between hematocrit and the log of erythropoietin excretion. Patients with hypoxia-induced erythrocytosis had increased levels of urinary erythropoietin when their hematocrit was reduced to normal levels by phlebotomy. Three patients whose erythrocytosis was associated with tumors had an erythropoietin excretion which remained constant over a wide range in hematocrit. In polycythemia vera, erythropoietin output was absent or markedly decreased at high hematocrit levels, but measurable erythropoietin appeared in the urine when the hematocrit was reduced to normal or anemic levels by bleeding.