Executive summary
- Think B12/folate deficiency with macrocytosis, glossitis, neuropathy/cognitive change, malabsorption, vegan diet, or metformin/PPI use.
- Do not give folate alone if B12 deficiency is possible (neurological harm risk).
- B12 replacement (CKS): hydroxocobalamin 1 mg IM on alternate days until no further improvement, then maintenance per cause.
Work-up (starter set)
- FBC + film, B12 + folate, ferritin/iron studies, TSH/LFTs; consider coeliac screen if indicated.
- Consider intrinsic factor antibodies if pernicious anaemia suspected (local pathway).
Treatment and referral
- Maintenance often: IM hydroxocobalamin every 2–3 months in irreversible causes (e.g. pernicious anaemia) — follow local guidance.
- Folate deficiency: folic acid (often 5 mg daily) after confirming B12 status and addressing cause.
- Urgent referral if severe symptomatic anaemia, pancytopenia, neurological deficits, or poor response.
Frequently asked questions
How fast do counts improve?
Reticulocytosis and Hb rise over weeks. Neurological recovery can take longer and may be incomplete if prolonged.
Can metformin lower B12?
Yes—consider B12 testing if symptoms or long-term metformin use with risk factors.
Transparency
This page is an educational, clinician-written summary of publicly available NICE guidance intended for trained healthcare professionals. It uses original wording (not copied text) and should be used alongside the full NICE source, local pathways, and clinical judgement. Doses provided are for general reference; always check the BNF/SPC.