LAUSR

Background: Reticulocyte haemoglobin content, i.e., the reticulocyte equivalent (Ret-He), seems to be a promising parameter for the detection of iron deficiency (ID) in neonates because it can be obtained as part of a reticulocyte count, with no additional blood loss and at no extra cost. Due to the short life span of reticulocytes, Ret-He reflects current iron availability for erythropoiesis more accurately than other common erythrocyte indices. Objective: We aimed to evaluate postnatal changes in Ret-He within the first days after birth in term and preterm infants with the hypothesis that preterm infants experience a more pronounced postnatal reduction in Ret-He when compared to term infants. Methods: We conducted retrospective analyses of clinically indicated blood samples. Paired t test and mixed regression modelling were used. Results: In total, 805 blood samples obtained from 207 term and 295 preterm infants were analysed. Ret-He decreased by 1.5 pg per day (regression coefficient [95% CI] -1.5 [-1.8 to -1.2] pg, p < 0.0001). This drop was more significant in preterm infants (regression coefficient -2.2 [-2.6 to -1.8] pg, p < 0.0001) than in term infants (regression coefficient -0.8 [-1.3 to -0.2] pg, p < 0.01, pinteraction < 0.0001). Conclusion: Ret-He declined within the first days after birth. The observed changes with postnatal age were more pronounced in preterm than in term infants. Further studies are needed to evaluate if these changes are due to developing ID or other causes.