Serum soluble transferrin receptor concentrations in US preschool children and non-pregnant women of childbearing age from the National Health and Nutrition Examination Survey 2003-2010

► We examine the distribution of sTfR and developed assay-specific cutoff values for defining elevated sTfR. ► US preschool children have higher sTfR concentrations than non-pregnant women of childbearing age. ► sTfR concentrations differed by age in both children and non-pregnant women and by gender in children. ► Cutoffs for defining elevated sTfR are 6.00 mg/L for children and 5.33 mg/L for non-pregnant women.