Iron deficiency is the most common nutritional deficiency globally — affecting an estimated 1.2 billion people, with women of reproductive age, pregnant women, and children under 5 disproportionately affected. In the United States, 35% of premenopausal women and 10% of women aged 12–49 have iron deficiency anemia — figures that have not meaningfully improved in 30 years despite iron being a solved nutritional science problem. What has changed is understanding of the spectrum of iron deficiency: non-anemic iron deficiency (ferritin below 30 ng/mL with normal hemoglobin) causes significant symptoms — fatigue, cognitive impairment, exercise intolerance, hair loss, restless legs syndrome — in millions of women who receive a normal CBC result and are sent home without diagnosis or treatment.
Why Hemoglobin-Only Screening Fails
Standard clinical practice screens for iron deficiency by measuring hemoglobin on a complete blood count. But iron stores become depleted through three sequential stages: iron depletion (ferritin falls), iron-deficient erythropoiesis (transferrin saturation falls, hemoglobin production impaired), and iron deficiency anemia (hemoglobin falls below threshold). Approximately 35% of women with documented ferritin depletion have normal hemoglobin — they have iron deficiency without anemia — yet most guidelines and clinical practice focus on anemia as the diagnostic endpoint. The clinical consequences are significant: cerebral iron deficiency impairs dopamine synthesis (explaining cognitive slowing and mood changes), mitochondrial iron stores affect aerobic energy production (explaining exercise intolerance even without anemia), and iron-dependent thyroid peroxidase affects thyroid hormone synthesis (potentially contributing to subclinical hypothyroidism).
Optimal Ferritin Target
Laboratory reference ranges for ferritin typically include values as low as 12–15 ng/mL as "normal" — these ranges were derived from populations with high iron deficiency prevalence and reflect the statistical distribution of a nutritionally deficient population rather than a health-optimizing threshold. Expert clinical consensus — supported by studies showing resolution of symptoms with iron repletion at ferritin levels of 15–50 ng/mL — suggests targeting ferritin above 50 ng/mL for symptomatic premenopausal women, above 30 ng/mL as a minimum, and above 70–100 ng/mL during pregnancy. Clinicians managing women's health should routinely order ferritin alongside a CBC when investigating fatigue, hair loss, or exercise intolerance.
Treatment: Oral vs. IV Iron
Oral iron supplementation — ferrous sulfate, ferrous gluconate, or iron bisglycinate (better tolerated) — is first-line for mild-to-moderate deficiency in the absence of malabsorption. Dosing every other day (rather than daily) increases absorption by exploiting hepcidin cycling — a 2017 Blood study found alternate-day dosing absorbed 40% more iron per dose than daily dosing. IV iron — ferric carboxymaltose (Injectafer), ferric derisomaltose (Monoferric), iron sucrose (Venofer) — provides complete iron repletion in a single or two infusions, bypassing gastrointestinal absorption limitations and intolerance. The IRONOUT HF trial demonstrated intravenous but not oral iron improved exercise capacity in heart failure, and IV iron is now first-line for iron deficiency in pregnancy after the second trimester and in all patients with inflammatory bowel disease. Healthcare facilities providing infusion services should maintain adequate stocks of IV supplies for iron infusion programs.
