Macrocytic anaemia from B12 / folate deficiency causing impaired DNA synthesis.
Etiology
- • B12: pernicious anaemia, vegan, ileal disease, metformin/PPI
- • Folate: alcoholism, pregnancy, haemolysis, methotrexate
History taking
- • Fatigue, glossitis, paraesthesia (B12)
- • Dietary history, alcohol
Examination
- • General: vitals, pallor, icterus, oedema, lymphadenopathy
- • Focused system examination
- • Look for red-flag findings
Red flags
- • Haemodynamic instability
- • Rapid deterioration
- • Severe pain or new neurological deficit
Differential diagnosis
- • See differentials section per chief complaint
Recommended investigations
- • CBC + smear: macro-ovalocytes, hypersegmented neutrophils
- • B12, folate (red cell), reticulocytes, LDH, bilirubin
- • Anti-IF / parietal antibodies if PA suspected
Diagnosis
- • Clinical diagnosis supported by targeted investigations
Initial treatment / management
- • Treat underlying cause
- • Symptomatic relief
- • Patient education
Drug therapy
- • IM hydroxocobalamin 1 mg alternate-day × 6 doses then 3-monthly
- • Folic acid 5 mg OD × 4 months (ensure B12 replete first)
Follow-up advice
- • Review in 2–4 weeks or earlier if worsening
- • Monitor response to therapy and adverse effects
Patient counselling
- • Explain diagnosis and natural course in lay terms
- • Red-flag symptoms warranting urgent return
- • Adherence to medications and follow-up
Referral criteria
- • Refer if diagnostic uncertainty, complications, or failure of first-line therapy
Clinical pearls
- • Replace B12 BEFORE folate to avoid subacute combined degeneration
References
- • Harrison's Principles of Internal Medicine, 21e
- • NICE / WHO guidelines (current edition)
Educational outpatient guide — verify against local guidelines before clinical use.
