Serum erythropoietin levels in term and preterm infants during the first year of life.

Purpose: To evaluate the kinetics of erythropoietin (EPO) production and address the pathogenesis of anemia of prematurity, we measured EPO levels in infants during the first year of life.

Patients and methods: Using a radioimmunoassay, serum EPO levels were measured in 97 infants classified into three groups according to weight: group A, n = 40, < 1,500 g; group B, n = 19, 1,500-2,499 g; and group C, n = 38, > or = 2,500 g.

Results: The serum EPO level ranged widely during the early neonatal period from days 0 to 6 (group A, < 5 to 307 mU/ml; group B, 10-340 mU/ml; and group C, 9-108 mU/ml). EPO reached its lowest level (< 20 mU/ml) between days 7 and 50 in all groups. The hemoglobin concentration reached its nadir between days 51 and 150 in all groups, with the lowest concentration observed in low birth weight infants. In contrast, the EPO level during the anemic phase was approximately 20 mU/ml and was independent of birth weight. A negative correlation between serum EPO level and hemoglobin concentration was observed only in group C (r = -0.54, p < 0.05). The negative slope of the regression equation in group C exceeded that of groups A and B (p < 0.05). When the relationship between EPO and Hb was evaluated over periods of 7-50 days, 51-100 days, and > 101 days, respectively, we noted a significant correlation between values on days 7 and 50 in group A (r = -0.53, p < 0.05) and between days 51 and 100 in group B (r = -0.76, p < 0.05).

Conclusions: These data suggest the appreciable EPO production in premature infants, but its insufficient response to the depressed hemoglobin level, implying the need to administer exogenous EPO to infants with anemia of prematurity.