Developmental Trends in Serum Iron, Transferrin, and Transferrin Saturation From Birth to 12 Months

AIM: There is a need for updated reference intervals for iron status biomarkers during infancy. This study aimed to investigate reference interval trends and diurnal variation of iron, transferrin, and transferrin saturation in infants subjected to delayed cord clamping at birth (DCC). METHODS: Data analysis from population-based Swedish studies, including 362 term-born infants subjected to DCC ≥ 60 s. The 2.5th and 97.5th percentiles were calculated from serum samples: In cord blood, at 48-118 h, four months and 12 months. We used Spearman's rho to test for associations and Student's t-test to compare groups. RESULTS: Iron concentrations in cord blood were initially high, 14-41 μmol/L, and had decreased by 48-118 h to 6-16 μmol/L, remaining mainly constant thereafter. Conversely, early transferrin concentrations were low. Transferrin slowly increased; concentrations at 4 months were positively associated with the average weight gained per day, rho = 0.46, p < 0.001. A small diurnal difference in iron was observed at 48-118 h: Samples collected between 10:30-11:59 were, on average, 1.4 μmol/L (95% CI -2.8 to -0.0) lower compared with samples collected between 15:30-19:59. CONCLUSION: Developmental trends in iron, transferrin, and transferrin saturation in the first year of life need to be considered in the interpretation of test results from infants.