Objective: To determine plasma erythropoietin levels and their association with hemoglobin and reticulocyte counts in healthy term infants.
Design: We compared plasma erythropoietin levels measured in serial blood samples obtained every 4 weeks during the first 6 months of life with one another and with levels in term fetuses and healthy adults. Correlation analysis was applied to examine for associations of erythropoietin with hemoglobin and with reticulocyte count.
Results: Plasma erythropoietin levels were lowest in the first and highest in the second postnatal months, a pattern reciprocal to that observed for hemoglobin during the period of physiologic anemia. The erythropoietin level was negatively correlated with hemoglobin (p < 0.0001) and positively correlated with reticulocytes (p < 0.0001). The slope of the inverse relationship of hemoglobin and plasma erythropoietin in infants was similar to those previously reported for anemic fetuses and premature infants, but much less steep than for anemic children and adults.
Conclusion: This study is the first to report simultaneous patterns of change observed in plasma erythropoietin, hemoglobin, and reticulocytes during normal infancy. These patterns are consistent with postnatal perturbations in tissue oxygenation and suggest a major role for erythropoietin in the regulation of erythropoiesis during normal infancy, but at a lower hemoglobin concentration than for older children and adults with pathologic anemia.