Decreased response of plasma immunoreactive erythropoietin to “available oxygen” in anemia of prematurity

Erythropoietin, hemoglobin, hematocrit, oxygen affinity (P 50), and reticulocyte counts were measured weekly starting at 1 week of age in 10 very-low-birth-weight infants and on a single occasion in 15 healthy men. In the adults, “available oxygen” (derived from oxygen carrying capacity and P 50) averaged 13.1 ml/dl blood and the mean erythropoletin level was 15.2 mU/ml. Erythropoietin levels in the infants were inversely related to concentration of hemoglobin, P 50 and available oxygen. However, despite the much lower mean “available oxygen” of 9.3 ml/dl in the infants compared with that in adults ( P