In a 23‑year‑old woman with iron‑deficiency labs (iron saturation 5 %, serum iron 23 µg/dL, total iron‑binding capacity 457 µg/dL, unsaturated iron‑binding capacity 434 µg/dL, ferritin 10 ng/mL, low MCV and MCHC) and a hemoglobin of 11.9 g/dL, should oral iron supplementation be started?

Should Oral Iron Supplementation Be Started in This 23‑Year‑Old Woman?

Yes—start oral ferrous sulfate 200 mg (≈65 mg elemental iron) once daily immediately, without waiting for further work‑up, because her laboratory profile confirms absolute iron deficiency (ferritin 10 ng/mL, transferrin saturation 5 %) and her hemoglobin of 11.9 g/dL meets WHO criteria for anemia in adult women (< 12.0 g/dL). 1, 2, 3

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Why Treatment Is Indicated Despite "Normal" Hemoglobin

• Ferritin < 30 ng/mL definitively confirms absolute iron deficiency in individuals without inflammation, and her ferritin of 10 ng/mL is well below this threshold. 1, 2
• Transferrin saturation < 16–20 % signals iron deficiency requiring treatment, and her saturation of 5 % is profoundly low. 1, 2
• Hemoglobin 11.9 g/dL is anemic by WHO criteria (< 12.0 g/dL in adult women), so this is iron‑deficiency anemia, not merely iron deficiency without anemia. 1, 3
• Low MCV and MCHC confirm microcytic, hypochromic anemia, the hallmark morphology of iron‑deficiency anemia. 4
• Even if her hemoglobin were "normal," iron deficiency itself causes symptoms—fatigue, exercise intolerance, difficulty concentrating, restless legs syndrome, and pica—that warrant treatment independent of anemia. 3

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First‑Line Oral Iron Regimen

• Ferrous sulfate 200 mg (≈65 mg elemental iron) taken once daily on an empty stomach in the morning is the gold‑standard, most cost‑effective oral formulation. 1, 2, 5, 3
• Add vitamin C 500 mg with each iron dose to enhance absorption by forming a soluble chelate and reducing ferric to ferrous iron—especially critical when transferrin saturation is as low as 5 %. 1, 2, 6
• Once‑daily dosing is superior to multiple daily doses because a single dose ≥60 mg triggers hepcidin elevation lasting 24–48 h, reducing absorption of subsequent doses by 35–45 % and increasing gastrointestinal side effects without improving hemoglobin response. 1, 2, 6, 5
• If daily dosing causes intolerable gastrointestinal side effects, switch to alternate‑day dosing with 100–200 mg elemental iron; this markedly increases fractional iron absorption, reduces side effects, and maintains overall efficacy, though the early rate of hemoglobin rise may be slower. 1, 2, 6, 5
• Alternative formulations (ferrous fumarate ≈70–105 mg elemental iron or ferrous gluconate ≈35–38 mg elemental iron) provide equivalent efficacy if ferrous sulfate is not tolerated, although they are generally more expensive. 1, 2, 5

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Expected Hemoglobin Response and Monitoring

• Check hemoglobin at 2–4 weeks; an increase of ≥10 g/L (≈1 g/dL) predicts treatment success with 90 % sensitivity and 79 % specificity. 1, 2
• Failure to achieve a ≥10 g/L rise by 2 weeks strongly predicts overall treatment failure and warrants evaluation for non‑adherence, ongoing blood loss, malabsorption, or concurrent vitamin B12/folate deficiency. 1, 2
• Continue oral iron for 3 months after hemoglobin normalizes to fully replenish iron stores; total treatment duration is typically 6–7 months. 1, 2, 3
• Monitor hemoglobin and red‑cell indices every 3 months during the first year, then again after the second year. 1, 2

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Investigation of Underlying Cause

• In a 23‑year‑old premenopausal woman, assess menstrual blood loss first; menorrhagia, pregnancy, and breastfeeding account for iron deficiency in 5–10 % of menstruating women. 1, 3
• Screen for celiac disease with tissue transglutaminase IgA antibodies (present in 3–5 % of iron‑deficiency cases), as celiac disease is a common cause of malabsorption in young patients. 1, 3
• Test for Helicobacter pylori infection, which can contribute to iron deficiency. 1
• Gastrointestinal endoscopy is not indicated in women under 45 years without upper GI symptoms, alarm features, or a family history of colorectal cancer. 1

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When to Switch to Intravenous Iron

• Intolerance to at least two different oral iron preparations (e.g., ferrous sulfate and ferrous fumarate or gluconate). 1, 2, 3
• Lack of ferritin improvement after 4 weeks of compliant oral therapy despite adequate dosing and vitamin C supplementation. 1, 2
• Transferrin saturation remaining < 20 % after an adequate oral trial. 1, 2
• Active inflammatory bowel disease with hemoglobin < 10 g/dL, where inflammation‑induced hepcidin elevation impairs oral iron absorption and oral iron may exacerbate intestinal inflammation. 1, 2, 3
• Post‑bariatric surgery patients, in whom duodenal iron absorption is anatomically disrupted. 1, 2, 3
• Celiac disease with inadequate response to oral iron despite strict adherence to a gluten‑free diet. 1, 2, 3

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Critical Pitfalls to Avoid

• Do not prescribe multiple daily doses of oral iron; this increases gastrointestinal side effects without improving efficacy due to hepcidin‑mediated absorption blockade. 1, 2, 6, 5
• Do not discontinue iron therapy when hemoglobin normalizes; continue for an additional 3 months to restore iron stores. 1, 2, 3
• Do not persist with oral iron beyond 4 weeks without a hemoglobin rise; reassess adherence, malabsorption, ongoing blood loss, or need for intravenous iron. 1, 2
• Do not overlook vitamin C supplementation when the oral iron response is suboptimal. 1, 2, 6
• Do not miss celiac disease screening; its prevalence of 3–5 % in iron‑deficiency cases can lead to treatment failure if undetected. 1, 3
• Do not delay iron therapy while awaiting diagnostic work‑up, unless a colonoscopy is scheduled within days (iron can impair endoscopic visualization). 1