Is oxygen supply the only regulator of erythropoietin levels? Serum immunoreactive erythropoietin during the first 4 months of life in term infants with different levels of arterial oxygenation.

Serum immunoreactive erythropoietin (siEp) levels were measured in 35 full-term infants aged 0-13 weeks, 31 of whom had congenital heart disease. The infants displayed a wide range in arterial oxygen tension (PaO2) and oxygen saturation (SaO2). During the first days of life siEp varied widely with a range from less than 3 to more than 10,000 mIU/ml. The wide variation is consistent with findings in cord blood at term. The siEp levels did not correlate significantly with haemoglobin, haematocrit, PaO2, SaO2, or arterial oxygen content in the total sample, nor when the cohort was split up into different age groups. Cyanotic infants aged 2-13 weeks had significantly higher siEp concentrations than normal adults (p less than 0.001) and than children with cyanotic congenital heart disease, aged 4 months-10 years (p less than 0.001). The raised siEp levels in cyanotic children aged 2-13 weeks found in this study and the normal levels found in their older counterparts (4 months-10 years) (reported elsewhere) are consistent with the pattern observed in man and animals exposed to prolonged hypobaric hypoxia, in which after an initial rise in erythropoietin concentrations the levels fall to normal while increased erythropoiesis is sustained.