What oral elemental iron dose should be given to a non‑pregnant healthy adult with a transferrin saturation of 15%?

Oral Iron Supplementation for Iron Deficiency with Transferrin Saturation of 15%

For a non-pregnant healthy adult with transferrin saturation of 15%, prescribe 50–100 mg of elemental iron once daily in the morning on an empty stomach, ideally as ferrous sulfate 200 mg (providing 65 mg elemental iron). 1

First-Line Treatment Approach

• Ferrous sulfate remains the gold standard oral iron formulation due to its proven efficacy, excellent cost-effectiveness (approximately £1.00 per 28-day supply), and equivalent effectiveness to more expensive alternatives. 1, 2

• A transferrin saturation of 15% indicates iron deficiency requiring supplementation, as values below 20% suggest inadequate iron availability for erythropoiesis. 3

• The optimal dose is 50–100 mg elemental iron once daily, which balances efficacy with tolerability. 1, 2

Specific Dosing Recommendations

• Ferrous sulfate 200 mg tablet (containing 65 mg elemental iron) taken once daily is the recommended starting regimen. 1, 2

• Alternative ferrous salts may be substituted if ferrous sulfate is not tolerated:

  • Ferrous fumarate 324 mg (provides 106 mg elemental iron) 1
  • Ferrous gluconate (provides 37 mg elemental iron per tablet) 1

• No oral iron formulation has demonstrated superiority in efficacy or tolerability over others; all ferrous salts are considered therapeutically equivalent. 1, 2

Optimal Administration Strategy

• Take iron in the morning on an empty stomach (1–2 hours before meals) to maximize absorption, as food can reduce absorption by up to 50%. 1, 4, 5

• Co-administer with 250–500 mg vitamin C (or a glass of orange juice) to enhance iron absorption through chelate formation. 1, 4, 5

• Avoid coffee, tea, and calcium-containing foods for at least 1–2 hours after dosing, as these substances significantly inhibit iron absorption. 1, 4, 5

• Once-daily dosing is superior to multiple daily doses because iron doses ≥60 mg trigger hepcidin elevation that persists for 24 hours, reducing absorption of subsequent doses by 35–45%. 1, 2, 4

Alternative Dosing if Standard Regimen Not Tolerated

• Alternate-day dosing (every other day) with 100–200 mg elemental iron significantly increases fractional iron absorption compared to daily dosing while reducing gastrointestinal side effects. 1, 2, 4

• If gastrointestinal symptoms are intolerable despite alternate-day dosing, consider taking iron with small amounts of food, though this reduces absorption. 4

• Ferric maltol 30 mg twice daily may be considered for patients with previous intolerance to traditional ferrous salts, though it costs significantly more (£47.60 vs £1.00 per 28 days) and provides slower iron loading. 1, 2

Monitoring Response to Treatment

• Check hemoglobin at 2 weeks: An increase of ≥10 g/L strongly predicts treatment success (sensitivity 90.1%, specificity 79.3%). 1, 2

• Recheck hemoglobin at 4 weeks to confirm adequate response and guide further management. 1, 2

• Continue treatment for approximately 3 months after hemoglobin normalizes to ensure adequate repletion of iron stores, not just correction of anemia. 1, 2, 4

When to Consider Intravenous Iron

• Switch to IV iron if:

  • No hemoglobin improvement after 2–4 weeks of adherent oral therapy 1, 2
  • Intolerable gastrointestinal side effects despite dosing modifications 1, 2
  • Conditions impairing oral iron absorption (inflammatory bowel disease, post-bariatric surgery, chronic kidney disease) 1, 2
  • Severe anemia (hemoglobin <10 g/dL) requiring rapid correction 2

• Modern IV formulations such as ferric carboxymaltose or ferric derisomaltose can replenish total body iron stores in one or two infusions of 500–1000 mg. 1, 6

• IV iron produces a clinically meaningful hemoglobin response within one week and should be considered as an alternative to blood transfusion. 1, 2

Formulations to Avoid

• Modified-release iron preparations are discouraged because they release iron beyond the duodenum (the primary absorption site) and show uniformly low absorption. 1, 2

• Multivitamin products containing ≤14 mg elemental iron are insufficient for treating iron deficiency and should not be relied upon as the sole iron source. 1

Common Pitfalls to Avoid

• Do not prescribe multiple daily doses, as this increases side effects without improving absorption due to hepcidin-mediated blockade. 1, 2, 4

• Do not discontinue therapy prematurely when hemoglobin normalizes—continue for 3 months to replenish iron stores. 1, 2

• Do not switch between different ferrous salts expecting better tolerability, as evidence does not support improved tolerance with different formulations. 1

• Verify medication interactions, particularly with proton pump inhibitors, which can significantly impair iron absorption. 2