Erythropoietin in premature infants.

The regulation of erythropoiesis during the first three months of life was studied in 30 premature infants who had haemoglobin concentrations which were lower than in term in fants of the same postdelivery age. Erythropoietin and erythropoiesis inhibitors were measured by means of an exhypoxic polycythaemic mouse bioassay. The percentage of haemoglobin F was determined as well. An increased erythropoietin level was detected only in six infants older than six weeks, whose blood haemoglobin concentration was lower than 100 g/l, while in serum from other babies erythropoietin was undetectable by the method used. Erythropoiesis inhibitors were present in 80% of the samples tested. The results presented indicate that in premature infants erythropoiesis is regulated through erythropoietin and that inhibitors of erythropoiesis take part in this regulation as well, but that the haemoglobin level at which erythropoietin is increased is lower in preterm infants than in term babies.