Infants are at risk for iron deficiency. Despite research advances, assessing iron stores during infancy remains a challenge to the clinician. Ferritin is the first-choice laboratory marker for measuring iron stores but it is today still unclear how to evaluate reference intervals among infants. We have studied Swedish infants (n = 456), born at term after normal pregnancies. Ferritin was measured at birth (umbilical cord sample), 48–72 h, 4 months and 12 months. Lower and upper reference interval limits were constructed as the 2.5th and 97.5th percentiles. By a large study population, we were able to use more stringent measures to avoid interference from the acute phase response than previous reports on ferritin reference intervals. When we used mathematical transformation we furthermore avoided potential information loss in precision and confirmed earlier reports of sex differences. At the lower reference interval limits there were small differences between sexes. For the higher limits, the differences were more pronounced in the older infant. At 0–3 d of age we observed a difference between the sexes of only 5% at the upper limits. The differences peaked at 12 months, where the boys’ upper 97.5th percentile was 56% compared to girls.

婴儿有缺铁的危险。尽管研究取得了进展，但在婴儿期评估铁储量仍然是临床医生面临的挑战。铁蛋白是测量铁储量的首选实验室标志物，但如今仍不清楚如何评估婴儿的参考间隔。我们研究了瑞典婴儿（n = 456），在正常怀孕后足月出生。在出生时（脐带样本），48-72小时，4个月和12个月测量铁蛋白。参考间隔的上限和下限被构造为2.5％和97.5％。与以前有关铁蛋白参考间隔的报道相比，在大量研究人群中，我们能够采取更严格的措施来避免急性期反应的干扰。当我们使用数学变换时，我们还避免了精确度方面的潜在信息损失，并确认了性别差异的早期报道。在较低的参考间隔下限，性别之间的差异很小。对于更高的限值，在较大的婴儿中差异更加明显。在0至3 d的年龄段，我们观察到性别的上限差异仅为5％。差异在12个月达到顶峰，