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Vitamin B12

Checked: 17-06-2025 by Rob Adams Next Review: 17-06-2027

Vitamin B12 deficiency - Overview

***UPDATE JUNE 2025***

The BNSSG Vitamin B12 Deficiency Guidelines (1) have now been published. They include advice for primary care on testing, interpretation, further investigation, treatment and follow up.

Prevalence

It is estimated that 1-2% of the general population have vitamin B12 deficiency and around ten times this in older adults.

Reference Ranges

UHBW reference ranges and interpretation advice are now harmonised with NBT – for further information contact the duty biochemist at either department (NBT- 01174148437, UHBW- 01173122469).

Repeat vitamin B12 testing for patients on replacement therapy

Please do not send requests for vitamin B12 levels for patients established on long term replacement therapy as this is unnecessary and uninformative.

Metformin and vitamin B12

MHRA advice was published in June 2022 stating the following:

'Decreased vitamin B12 levels, or vitamin B12 deficiency, is now considered to be a common side effect in patients on metformin treatment, especially in those receiving a higher dose or longer treatment duration and in those with existing risk factors. We are therefore advising checking vitamin B12 serum levels in patients being treated with metformin who have symptoms suggestive of vitamin B12 deficiency. We also advise that periodic monitoring for patients with risk factors for vitamin B12 deficiency should be considered.' (3)

Referral

Patients with vitamin B12 or folate deficiency do not normally require referral for haematology outpatient assessment.

Haematology advice and guidance can be requested if uncertainty regards management persist.

Pregnancy

Vitamin B12 testing should be avoided in pregnancy as results are unreliable (levels naturally decrease in pregnancy). If clinical suspicion of deficiency is strong, consider testing but interpret the results with caution. Discussion with the laboratory and additional tests may be needed. An alternative approach may be a short course of therapy and reassessment post-pregnancy.

Elevated vitamin B12 levels

This is often a non-pathological finding and rarely due to a haematological condition. The most common cause of high vitamin B12 in the absence of B12 replacement therapy is liver disease. Vitamin B12 may be elevated in haematological malignancy including myeloproliferative disorders and these disorders are excluded by a normal FBC.

Assessment in Primary Care

Check that the patient has not been taking supplements that include vitamin B12.

Assess general health and for risk factors for liver disease.

Investigations in Primary care:

These will be determined by the clinical history examination and blood results. Unless a haematological malignancy is suspected from the FBC report, discussion with or referral to Haematology is not required. Assessment for liver disease may be appropriate.

Resources

(1) 9. Nutrition and Blood Guidelines (Remedy BNSSG ICB)

(2) Vitamin B12 deficiency in over 16s: diagnosis and management (NG239)- Please note that there is substantial variation between Total Vitamin B12 analytical methods, hence local reference ranges must be used for the local analytical method and NICE NG239 thresholds do not apply (because of the local method performing much lower compared with other analytical methods).

(3) Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk - GOV.UK (www.gov.uk)

Efforts are made to ensure the accuracy and agreement of these guidelines, including any content uploaded, referred to or linked to from the system. However, BNSSG ICB cannot guarantee this. This guidance does not override the individual responsibility of healthcare professionals to make decisions appropriate to the circumstances of the individual patient, in consultation with the patient and/or guardian or carer, in accordance with the mental capacity act, and informed by the summary of product characteristics of any drugs they are considering. Practitioners are required to perform their duties in accordance with the law and their regulators and nothing in this guidance should be interpreted in a way that would be inconsistent with compliance with those duties.

Information provided through Remedy is continually updated so please be aware any printed copies may quickly become out of date.