Peripheral haematocrit modulates erythropoietin production and kinetics of reticulocytes in chronic uraemic patients.

Determination of reticulocytes (RETI), haematocrit (HCT) and serum erythropoietin (by radioimmunoassay = EP-RIA) before and after transfusions of 500ml red blood cells (RBC) into 15 chronic uraemic patients demonstrated that there was a converse relation between both of these, EP-RIA and RETI, and the HCT. The same conditions were found in cases of spontaneous bleeding. This pattern of reaction of RETI, EP-RIA and HCT suggested a feedback circuit, operative between these three parameters in chronic uraemic patients.