Cut‐off points for serum ferritin to identify low iron stores during the first year of life in a cohort of Mexican infants

The aim of this study was to identify serum ferritin (SF) cut‐off points (COPs) in a cohort of healthy full‐term normal birth weight infants who had repeated measurements of SF and haemoglobin every 3 months during the first year of life. The study included 746 full‐term infants with birth weight ≥2,500 g, having uncomplicated gestations and births. Participants received prophylactic iron supplementation (1 mg/day of iron element) from the first to the 12th month of life and did not develop anaemia during the first year of life. Two statistical methods were considered to identify COPs for low iron stores at 3, 6, 9 and 12 months of age: deviation from mean and cluster analysis. According to the K‐means cluster analysis results by age and sex, COPs at 3 and 6 months for girls were 39 and 21 μg/L and for boys 23 and 11 μg/L, respectively. A single COP of 10 μg/L was identified, for girls and boys, at both 9 and 12 months. Given the physiological changes in SF concentration during the first year of life, our study identified dynamic COPs, which differed by sex in the first semester. Adequate SF COPs are necessary to identify low iron stores at an early stage of iron deficiency, which represents one of the most widespread public health problems around the world, particularly in low‐ and middle‐income countries.