Erythropoietin excretion in the premature infant.

Urinary erythropoietin was determined sequentially in four premature infants throughout their period of physiologic anemia. After the first day of life, no erythropoietin was found, even though there was a marked fall in hematocrit. Among seven premature infants with severe respiratory disease, three excreted elevated amounts of erythropoietin. Premature infants appear able to respond to hypoxia by increasing erythropoietin production. In the absence of hypoxia, however, diminution of erythropoiesis in the early weeks of life is not accompanied by elevated excretion of erythropoietin.