Serum transferrin receptor, ferritin, and reticulocyte maturity indices during the first year of life in 'large' preterm infants

BACKGROUND: Preterm infants are at risk of developing iron deficiency; among the iron status and hemopoiesis indices the serum transferrin receptor (sTfr) has been shown to be a useful indicator in assessing iron status, while immature reticulocyte production is regarded as an estimator of erythropoiesis. OBJECTIVE: To investigate age-related changes in iron status infants born 'moderately' preterm, with a gestational age (GA) of 32-36 wk, and identify associations between sTfr and other hematological and biochemical iron indices. DESIGN: Hospital-based prospective, longitudinal study in preterm infants. METHODS: Iron and erythropoiesis parameters were evaluated in 181 formula-fed preterm infants at 2 and 6 wk and 3, 6, 9, and 12 months chronological age. Hemoglobulin (Hb), hematocrit (Hct), mean corpuscular volume (MCV), reticulocytes, serum iron (sFe), serum ferritin (sFer), sTfr, and reticulocyte subpopulations were measured. RESULTS: A total of 756 measurements were performed. After an initial decline, Hb rose from month 3 to 12 of life. SFe and sFer and immature reticulocyte count decreased from the second week to the third month and remained stable thereafter. STfr was lower up to 6 wk and stable from month 3 to 12. Iron deficiency anemia (IDA) was found in 5.5% of infants. In 76 measurements sFer was <12 microg/L, implying storage iron deficiency (SID). A negative correlation was observed between sTfr and other indices of iron status such as Hb, Hct, MCV, sFe, and sFer. Infants with sFer <12 microg/L had lower sTfr than those with sFer >12 microg/L. Reticulocyte production was positively associated with STfr, but this association was dependent on the chronological age of the infant. CONCLUSION: Iron depletion is common in formula-fed preterm (32-36 wk GA) infants between month 3 and 12 of life. STfr appears to be an indicator of iron status in preterm infants during the first year of life.