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Iron deficiency anaemia and the differential diagnosis of microcytic anaemia
A low ferritin (below 30 µg/L) diagnoses iron deficiency; in an adult — especially a man or a postmenopausal woman — iron deficiency is gastrointestinal blood loss until proven otherwise, so alongside iron treatment a gastroscopy and colonoscopy are performed.
Why it matters in the exam
Microcytic anaemia questions test the distinction between four possibilities: iron deficiency (low ferritin, low TSAT, high RDW), anaemia of chronic disease (normal or high ferritin, low TIBC), thalassaemia trait (normal or high red cell count, a very low MCV relative to the haemoglobin, normal ferritin; HbA2 above 3.5% in beta-thalassaemia) and sideroblastic anaemia (ring sideroblasts in the marrow; lead, alcohol, B6 deficiency). Active inflammation raises ferritin, so even a value up to 100 can fit iron deficiency.
The second part is investigation and treatment. In a man or a postmenopausal woman with iron deficiency anaemia and no clear cause, gastroscopy with duodenal biopsies and colonoscopy are performed, and coeliac serology (anti-tTG) is checked. Oral iron is given once a day or even every other day, because frequent doses raise hepcidin and reduce absorption. A good response is a haemoglobin rise within about two weeks, and treatment continues for 3 months after correction to refill the stores. Intravenous iron suits intolerance, malabsorption (coeliac disease, after bariatric surgery), chronic kidney disease, heart failure or a need for rapid correction.
Key points
- Ferritin below 30 µg/L = iron deficiency; with inflammation up to 100 with TSAT below 20%.
- Man or postmenopausal woman: gastroscopy, colonoscopy and anti-tTG.
- Thalassaemia: normal or high RBC count, normal ferritin, HbA2 above 3.5%.
- Oral iron once a day or every other day; intravenous for malabsorption, intolerance, CKD or heart failure.
- Continue for 3 months after the haemoglobin is corrected.
Summary table
| Diagnosis | Ferritin / iron | Distinguishing feature | Next step |
|---|---|---|---|
| Iron deficiency | Ferritin below 30 µg/L, TSAT below 20% | High RDW, high TIBC | Find the source of bleeding, give iron |
| Anaemia of chronic disease | Normal or high ferritin, low TIBC | Inflammatory disease, infection, malignancy | Treat the underlying disease |
| Beta-thalassaemia trait | Normal ferritin | Normal or high RBC count; HbA2 above 3.5% | Electrophoresis; do not give iron |
| Sideroblastic anaemia | High iron | Ring sideroblasts | Lead, alcohol, B6, MDS |
| Iron deficiency with inflammation | Ferritin up to 100 µg/L with TSAT below 20% | High CRP | Treat as iron deficiency |
A free exam question
בן 35 , ברקע rheumatoid arthritis לא מטופל. בבדיקות הדם שלו התפתחות של אנמיה עם המוגלובין 8.4 gr/dl ו- MCV 80fl , ספירת רטיקולוציטים 1.1% . איזה מהבאים מסביר את הפתוגנזה של האנמיה של חולה זה? (the question as examined, in Hebrew)
- א. ירידה ברמות hepcidin מדכאות ספיגת ברזל מהמעי ומזרזות יצי את ברזל מהפטוציטים וממקרופאג׳ים
- ב. ירידה ברמות hepcidin מזרזות ספיגת ברזל מהמעי ומעכבות יצי את ברזל מהפטוציטים וממקרופאג׳ים
- ג. עליה ברמות hepcidin מדכאות ס פיגת ברזל מהמעי ומזרזות יצי את ברזל מהפטוציטים וממקרופאג׳ים
- ד. עליה ברמות hepcidin מדכאות ספיגת ברזל מהמעי ומעכבות יצי את ברזל מהפטוציטים וממקרופאג׳ים
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Sources
- British Society of Gastroenterology Guidelines for the management of iron deficiency anaemia in adults, 2021 — Diagnosis, investigation and iron replacement
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Iron Deficiency and Other Hypoproliferative Anemias
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.
See also: in children: Iron-deficiency anaemia in children