DETERMINATION OF IRON-ABSORPTION USING ERYTHROCYTE IRON INCORPORATIONOF 2 STABLE ISOTOPES OF IRON (FE-57 AND FE-58) IN VERY-LOW-BIRTH-WEIGHT PREMATURE-INFANTS

Due to limited erythropoiesis, iron needs for the premature infant dur ing the first 2 months of life are low. With the potential for increas ed use of erythropoietin in the preterm infant, iron requirements may become markedly higher. The ability of the preterm infant to absorb ir on, therefore, becomes crucial. Previous studies using single stable i sotopes of iron without metabolic balances were unable to quantitative ly determine iron absorption since the percentage of absorbed iron app earing in the erythrocyte could not be measured. The objective of the current study was to determine iron absorption using the method of ery throcyte iron incorporation of two stable isotopes of iron given by th e enteral and parenteral route to very low birth weight (VLBW) infants , Results obtained were compared to iron absorption values from studie s using single isotopes and metabolic balance techniques. Six VLBW pre mature infants (gestational age 26.8 +/- 1.7 weeks, postnatal age 3.6 +/- 1.9 weeks, birth weight 863 +/- 117 g) were studied. Iron dosages were (i.v.) 0.15 mg/kg (FeSO4)-Fe-57 and (enteral) 1.5 mg/kg ((FeSO4)- Fe-58). Erythrocyte isotope ratios, Fe-57/Fe-54 and Fe-58/Fe-54, were determined by inductively coupled plasma mass spectrometry (ICP/MS) fr om single blood samples (100 mu l) collected before and after concurre nt enteral (Fe-58) and parenteral (Fe-57) administration of isotopes. Only 17.8% of the i.v.-infused iron dose was incorporated into hemoglo bin on day 15. Using a correction factor based on the percentage of i. v. iron (Fe-57) incorporated into erythrocytes, the corrected incorpor ation of Fe-58 was calculated to be 26.3 +/- 13.0% of the enteral dose of (FeSO4)-Fe-58. This value is comparable to those obtained in previ ous studies, which utilized alternate techniques to measure iron absor ption.