Last Updated: March 18, 2026
Clinical Guidelines Summary
Quick reference guide to UK guidelines on B12 deficiency diagnosis and management.
NICE Clinical Knowledge Summaries
Anaemia - B12 and folate deficiency
When to Investigate
- Macrocytic anaemia (MCV >100 fL)
- Neurological symptoms consistent with B12 deficiency
- Risk factors: vegan/vegetarian diet, malabsorption conditions, gastric surgery
- Long-term metformin or PPI use
Recommended Tests
- First-line: Full blood count, serum B12, folate
- If borderline B12: Methylmalonic acid (MMA) or holotranscobalamin
- For pernicious anaemia: Intrinsic factor antibodies
British National Formulary (BNF)
Treatment protocols
Hydroxocobalamin Dosing
Without Neurological Involvement
1mg IM 3 times weekly for 2 weeks, then 1mg every 2-3 months
With Neurological Involvement
1mg IM on alternate days until no further improvement, then 1mg every 2 months
Note: Cyanocobalamin tablets may be appropriate for dietary deficiency in patients without absorption problems. Recommended dose: 50-150mcg daily between meals.
British Society for Haematology
Guidelines for diagnosis and treatment (2014)
Under Review
Key Recommendations
- 1Treat symptomatic patients with borderline serum B12 (below 300 ng/L)
- 2Serum B12 <200 ng/L is deficient; 200-300 ng/L is borderline
- 3MMA and homocysteine are more sensitive markers of tissue deficiency
- 4Neurological symptoms require urgent treatment - do not wait for blood results
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