Biochemical signs of impaired cobalamin function do not affect hematological parameters in young infants: results from a double-blind randomized controlled trial

Background: Whereas iron deficiency is considered the leading cause of anemia in infants, cobalamin deficiency is foremost characterized by developmental delay, and the typical macrocytic anemia is confined to severe and longstanding cobalamin deficiency in this age group. Hematological parameters were investigated in 4-mo-old infants with biochemical signs of impaired cobalamin function who participated in a randomized controlled cobalamin intervention study at 6 wk. Methods: One hundred and seven infants were randomly assigned to receive either an intramuscular injection with 400 μg cobalamin or no intervention at 6 wk. Hematological parameters, and cobalamin and folate status were determined at inclusion and 4 mo. Results: Cobalamin supplementation improved all markers of impaired cobalamin function but had no effect on hematological cell counts at 4 mo ( P > 0.18). Signs indicative of an iron-restricted erythropoiesis were observed at 6 wk and 4 mo. At 4 mo, the strongest predictors of low iron status were male gender and a high percentage weight increase from birth. Conclusion: In infants with biochemical signs of impaired cobalamin function, supplementation does not improve hematological cell counts. Variations in erythrocyte parameters seem to be foremost associated with iron status in this age group.