IRON-ABSORPTION AND INCORPORATION INTO RED-BLOOD-CELLS BY VERY-LOW-BIRTH-WEIGHT INFANTS - STUDIES WITH THE STABLE ISOTOPE FE-58

Measurements of iron absorption and incorporation into RBCs were obtained with the stable isotope Fe-58, administered as a reference dose, in 11 premature infants with birth weights between 780 and 1,520 g and gestational ages between 24 and 33 weeks. Each study included a timed stool and urine collection, nasogastric tube administration of a single dose of about 228 mug of Fe-58/kg of body weight (as FeSO4, with 10 mg/kg of vitamin C) between feedings, and blood samples before Fe-58 (day 1) and then 2 weeks (day 15) later. Gastrointestinal absorption of the Fe-58 dose as measured by fecal isotope balance was 41.6 +/- 17.6% (mean +/- SD). However, only 12.0 +/- 9.6% of the Fe-58 dose (28.7 +/- 22.3% of the absorbed Fe-58 dose) was incorporated into RBCs on day 15. Fe-58 absorption and Fe-58 incorporation into RBCs on day 15 were significantly correlated with the hemoglobin concentration and reticulocyte count on day 1. Transfusion history did not affect Fe-58 absorption or Fe-58 incorporation into RBCs. We conclude that concurrent measurement of Fe-58 absorption with fecal monitoring and of Fe-58 incorporation into RBCs permits a better understanding of the fate of iron ingested by premature infants than either measurement alone.