About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Microcytic hypochromic anaemia: low MCV, low MCH, low ferritin (most useful single test), low serum iron, raised TIBC
- Causes: blood loss (GI — most important to exclude; menorrhagia), poor intake, malabsorption (coeliac), increased demand (pregnancy)
- All men and post-menopausal women with IDA must have GI investigation (OGD + colonoscopy) to exclude malignancy
- Pre-menopausal women: GI investigation if GI symptoms, no obvious gynaecological cause, or failed to respond to iron
- Treatment: oral ferrous sulphate 200 mg BD–TDS (65 mg elemental iron per tablet). IV iron if intolerant, non-compliant, or malabsorption
Overview
Iron deficiency anaemia (IDA) is the most common cause of anaemia globally and the most common cause of microcytic anaemia. It results from an imbalance between iron intake/absorption and iron loss/utilisation. In developed countries, the most important cause in men and post-menopausal women is occult GI blood loss — making it mandatory to investigate for GI malignancy. In pre-menopausal women, menorrhagia is the commonest cause. Other important causes include malabsorption (coeliac disease), poor dietary intake, and increased demand (pregnancy, growth).
Epidemiology
IDA affects approximately 2–5% of adult men and post-menopausal women in the UK, and up to 20% of pre-menopausal women. Globally, iron deficiency affects over 2 billion people. GI malignancy (colorectal cancer, gastric cancer) is found in approximately 5–10% of men and post-menopausal women presenting with IDA. Coeliac disease accounts for ~5% of IDA cases. Risk groups include vegetarians/vegans, pregnant women, frequent blood donors, and patients on PPIs or H2 blockers (reduce iron absorption).
Clinical Features
Symptoms
Fatigue and lethargy — often the predominant symptom
Breathlessness on exertion
Palpitations
Headache, dizziness
Pica (craving non-food substances — ice, soil, chalk)
Restless legs
Rectal bleeding, melaena, or change in bowel habit (suggests GI cause)
Weight loss (suggests malignancy)
Signs
Pallor (conjunctival, palmar, nail bed)
Koilonychia (spoon-shaped nails)
Angular stomatitis (cracks at corners of mouth)
Glossitis (smooth, sore tongue)
Tachycardia, flow murmur (compensatory in severe anaemia)
Signs of underlying cause: abdominal mass, rectal mass on PR
Investigations
First-line
FBC and blood filmLow Hb, low MCV (<80 fL), low MCH. Film: microcytic hypochromic red cells, pencil cells, target cells
FerritinLOW ferritin (<30 µg/L) is the single most useful test — virtually diagnostic of iron deficiency. Note: ferritin is an acute phase reactant (can be falsely normal/high in infection/inflammation)
Iron studiesLow serum iron, raised TIBC (total iron binding capacity), low transferrin saturation (<20%)
Second-line
Coeliac screen (tTG-IgA)Check in ALL patients with IDA — coeliac disease is an important treatable cause
U&Es, LFTs, CRPBaseline bloods, inflammatory marker to aid ferritin interpretation
UrinalysisHaematuria — renal tract malignancy can present with IDA
Specialist
OGD + colonoscopyMANDATORY in all men and post-menopausal women with IDA — to exclude GI malignancy (BSG guidelines)
CT abdomen/pelvisIf both OGD and colonoscopy normal — small bowel pathology, renal/urological malignancy
Capsule endoscopyIf OGD and colonoscopy negative — assesses small bowel for angiodysplasia, Crohn's, tumours
1
Oral iron replacement
- Ferrous sulphate 200 mg BD–TDS (most commonly used — 65 mg elemental iron per tablet)
- Alternative: ferrous fumarate 210 mg BD (higher elemental iron content)
- Take on empty stomach with vitamin C (orange juice) to enhance absorption
- Warn patient: black stools, constipation, nausea — common side effects
- Continue for 3 months AFTER Hb normalises to replenish iron stores
2
IV iron
- Indications: oral iron intolerance, non-compliance, malabsorption, need for rapid correction (e.g. pre-operative, late pregnancy)
- IV ferric carboxymaltose (Ferinject) — single high-dose infusion (up to 1000 mg)
- Monitor for infusion reactions — give in a setting equipped for anaphylaxis management
3
Investigate and treat the cause
- GI investigation (OGD + colonoscopy) in men and post-menopausal women — mandatory
- Pre-menopausal women: assess menstrual history; GI investigation if symptoms, no gynae cause, or non-response to iron
- Treat coeliac disease with GFD
- Treat GI malignancy via appropriate pathway
- Review medications reducing absorption (PPIs, antacids) — reduce or stop if possible
4
Monitoring
- Recheck FBC at 2–4 weeks — Hb should rise by ~10–20 g/L per month
- If no response: reassess diagnosis, check compliance, consider malabsorption, ongoing blood loss, or incorrect diagnosis
- Check ferritin after 3 months of treatment (after Hb has normalised) to confirm stores replenished
Complications
- Underlying malignancy: Colorectal cancer is the most important diagnosis to exclude — IDA may be the first presentation
- Heart failure: Chronic severe anaemia can cause high-output cardiac failure
- Pica and pagophagia: Compulsive ice-eating — resolves with iron replacement
- Plummer-Vinson syndrome: IDA + oesophageal web + dysphagia — pre-malignant (risk of oesophageal SCC)
- Impaired cognitive development: In children with chronic iron deficiency
UKMLA Exam Tips
- 1Low ferritin = iron deficiency. Period. It is the MOST USEFUL single test (high specificity when low)
- 2ALL men and post-menopausal women with IDA need OGD + colonoscopy to exclude GI cancer — non-negotiable
- 3Ferritin is an acute phase reactant — can be falsely normal in inflammation. If CRP raised and ferritin "normal", iron deficiency is NOT excluded
- 4Oral iron: takes 3 months to normalise Hb, then continue for 3 MORE months to replenish stores
- 5Microcytic anaemia differential: Iron deficiency (most common), thalassaemia, anaemia of chronic disease (can be normocytic too), sideroblastic anaemia, lead poisoning
- 6Plummer-Vinson (Paterson-Kelly): IDA + dysphagia + oesophageal web — predisposes to oesophageal SCC
practicetest your knowledge on iron deficiency anaemiaApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — haematology and beyond.
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