Greater Glasgow and Clyde Medicines

Vitamin B12 Guideline Updated

The Vitamin B12: Treatment of Deficiency in Adults guideline has been updated.

Key changes

  • A key points summary and flowchart have been added at the beginning of the guideline.
  • Clarification that there is no necessity to treat low B12 levels caused by medicines (e.g. colchicine, metformin, long term Proton Pump Inhibitors (PPIs) or H2 blockers) in the absence of anaemia and/or neurological symptoms. This has been emphasised in the key points section, throughout the guideline, and in the flowchart in Appendix 2.
  • Previous advice was to sample intrinsic factor (IF) antibodies before starting B12 therapy because the assay in use gave false positive result if the B12 level was > 440pg/ml. This assay has now been replaced and a positive IF antibody result is now reliable even if the patient has started B12 replacement and has a high serum vitamin B12 level.
  • BNF dosage of hydroxocobalamin injection for pernicious anaemia and other macrocytic anaemias without neurological involvement has been updated - Initially 1 mg 3 times a week for 2 weeks, then 1 mg every 2-3 months (previously the BNF said every 3 months).

Refer to the previous blog on vitamin B12 for further information.


Published 17/08/2021. Link updated 08/03/2022.

Medicines Update blogs are correct at the time of publication.