Serum Erythropoietin and Hemoglobin Affinity for Oxygen in Patients Phlebotomized for Polycythemia Vera

Abstract

Serum erythropoietin (Ep) was measured by radioimmunoassay before and 24 hours after therapeutic phlebotomies in patients with polycythemia vera (PV) and in normal subjects before and after phlebotomies of comparable volumes. In addition the in vivo oxygen affinity of hemoglobin (P₅₀) was calculated, and red cell indices and 2,3 DPG values were measured. Paired t tests determined whether the differences between pre-and post--phlebotomy values were statistically significant.

Blood hemoglobin (Hb) levels declined after phlebotomy, and generally continued to be at or above normal levels. Serum E_p increased after phlebotomy in both groups of subjects. The in vivo P₅₀ value for patients with PV (29.4 + 0.4 mmHg) was significantly (_p<0.005) greater than the normal value (27.2 + 0.5).

Seven of the PV patients (5 males, 2 females) were restudied. Their Hb and hematocrit values were either normal or slightly higher than normal. The MCV for 4 males and 1 female was below normal. The MCHC was slightly lower than normal and reticulocytosis was not present. The male PV patients had greater than normal 2,3 DPG values and most had right-shifted P₅₀ values. There was no correlation between 2,3 DPG values and P₅₀ values. The female patients did not have 2,3 DPG values consistently greater than normal and their P₅₀ values were not right shifted.

These results showed that serum EP increased in response to small reductions in Hb even when subnormal Hb values were not produced. The reduced affinity of Hb in PV patients may explain earlier observations that patients with PV have lower levels of urinary or plasma E_p than normals with the same hematocrits.