Reticulocyte hemoglobin content as a function of iron stores at 35-36 weeks post menstrual age in very premature infants.

Background: Premature infants are born with lower iron stores and are at risk for iron deficiency during early infancy. To prevent iron deficiency, premature infants are routinely supplemented with 2 mg/kg/day oral elemental iron. Reticulocyte hemoglobin content (RET-He), a measure of iron deficiency, has not been well evaluated prior to discharge in premature infants.

Objectives: Our objectives were to evaluate RET-He and its correlation with serum ferritin (SF), an index of iron stores, at 35-36 weeks postmenstrual age (PMA) in ≤32 weeks gestational age (GA) infants.

Methods: We performed a prospective nested study involving 24-32 weeks GA infants who were receiving 2 mg/kg/day oral elemental iron with full enteral feedings at 35-36 weeks PMA. Infants with the following conditions were excluded: craniofacial malformation, chromosomal disorders, TORCH (toxoplasmosis, other infections, rubella, cytomegalovirus, and herpes simplex), culture-proven sepsis, C-reactive protein >5 mg/l within 10 days of iron status assessment, or erythropoietin therapy. SF and RET-He were measured at 35-36 weeks PMA using chemiluminescence immunoassay and Sysmex XN hematology analyzer, respectively. RET-He <27 pg was deemed indicative of iron deficiency.

Results: Ninety-eight infants were studied, of which 21 infants had RET-He <27 pg. There was a positive correlation between RET-He and SF (coefficient 0.22,  = .03) that remained significant after controlling for GA (coefficient 0.21,  = .03) and frequency of prior erythrocyte transfusions (coefficient 0.21,  = .03). On stratified analysis, there was a positive correlation between SF and RET-He in females ( = 52, coefficient 0.23,  = .02), but not in males ( = 46, coefficient 0.05).

Conclusions: Most premature infants receiving 2 mg/kg/day oral elemental iron are iron replete for erythropoiesis at 35-36 weeks PMA. RET-He increases with an increase in iron stores, suggesting that additional iron supplementation prior to discharge to very premature infants with borderline low RET-He may help prevent iron deficiency during early infancy.