Low serum B12 (<200 pg/mL) causing macrocytic anaemia ± neuropathy.
Risk factors
- • Vegan diet
- • Pernicious anaemia
- • Metformin, PPI long-term
- • Ileal resection, Crohn
History taking
- • Fatigue, glossitis, paraesthesia
- • Memory issues, ataxia
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
- • Serum B12, MMA / homocysteine if borderline
- • Anti-IF antibodies
- • CBC + smear
Diagnosis
- • Clinical diagnosis supported by targeted investigations
Initial treatment / management
- • Treat underlying cause
- • Symptomatic relief
- • Patient education
Drug therapy
- • IM hydroxocobalamin as above
- • Oral cyanocobalamin 1–2 mg OD if dietary
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
- • Neurological symptoms can occur without anaemia
References
- • Harrison's Principles of Internal Medicine, 21e
- • NICE / WHO guidelines (current edition)
Educational outpatient guide — verify against local guidelines before clinical use.
