34% of U.S. women under age 50 have iron deficiency under new guidelines

New 2026 guidance from the American Society of Hematology uses different ferritin cutoffs to identify iron deficiency according to a person’s circumstances. Ferritin reflects iron stored in the body, while transferrin carries iron in the blood for use in making hemoglobin and red blood cells. A level of 30 ng/mL or lower is the general adult threshold; 50 ng/mL or lower may be appropriate for people with symptoms or added risks, including heavy menstrual bleeding or plans for pregnancy. With inflammation, which can raise ferritin and obscure low iron, deficiency may be considered when ferritin is below 100 ng/mL or transferrin saturation is below 20%. The higher thresholds apply in defined situations, not as universal targets for supplementation.

Applying the 30 ng/mL cutoff to U.S. survey data, a study of 8,021 adults estimated iron deficiency in 34% of women ages 19-49, compared with 14% using the former 15 ng/mL cutoff. Estimates for men in that age range rose from 1% to 3%. Evidence that iron can reduce fatigue in some people without anemia includes trials in menstruating women: oral iron reduced fatigue more than placebo over 12 weeks, and intravenous iron produced a modestly higher response rate over eight weeks. However, these trials do not establish the ideal diagnostic cutoff or show that everyone with low ferritin benefits. The guidelines’ recommendations are conditional; people with prior ferritin results between 15 and 30 and fatigue are advised to discuss assessment, the cause of low iron, treatment, and follow-up with a clinician.