A RADIOIMMUNOASSAY FOR ERYTHROPOIETIN - SERUM LEVELS IN NORMAL HUMAN-SUBJECTS AND PATIENTS WITH HEMATOPOIETIC DISORDERS

Abstract

An RIA [radioimmunoassay] for Ep [erythropoietin] has been developed that is highly sensitive and specific. A homogeneous Ep preparation was labeled with 125I by the chloramine-T method to a specific activity of 90-136 .mu.Ci/.mu.g and immunoreactivity of 80%. Ep antiserum, which was produced to a human urinary Ep preparation (80 U/mg protein), was absorbed with normal human urinary and serum proteins without any loss in sensitivity of the RIA to increase the specificity of the assay. A good correlation was seen between the RIA and the exhypoxic polycythemic mouse assay (r = 0.967; slope 1.05 and y intercept 0.75). Ep titers in sera from 175 hematologically normal human subjects exhibited a normal frequency distribution and ranged between 5.8-36.6 m.+-./ml, with a mean of 14.9 .+-. 4.7 (SD) and median of 14.3. Serum Ep titers were markedly elevated in 7 patients with aplastic anemia and 1 patient with pure red cells aplasia (1350-20,640 mU/ml), and were lower than normal in 2 patients with polycythemia vera (8.1 and 9.4 mU/ml). The serrum Ep titers in a prenephrectomy patient with chronic glomerulonephritis (32.1 mU/ml) decreased to below normal levels (9.04 mU/ml) after nephrectomy. The cord serum erythropoietin titers in 10 IDM [infants of diabetic mothers] [90.82 .+-. 134.1 mU/ml] returned to values within the normal range (13.86 .+-. 5.55) on day 3 after birth, suggesting the utility of the RIA in elucidating the role of hypoxia and/or insulin in increased erythropoiesis in IDM. The serum Ep titers in patients with anemias and polycythemias were compared to those of normal human subjects and agreed well with pathophysiologic mechanisms of these hemopoietic disorders, confirming the validity of the RIA.