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Vitamin B12 - interim guidelines DRAFT

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Vitamin B12 deficiency - overview

Interim Guidelines

There is still some lack of consensus on appropriate testing for vitamin B12 and how it should be managed (1). The following advice is therefore a pragmatic approach to the testing and treatment of cobalamin disorders based on British Society of Haematology (1) and local guidelines (2) Further national guidelines are due to be published in January 2024 and we will endeavour to keep this page updated with any developments.

Reference Ranges

There is an update on new reference ranges for serum vitamin B12 on the NBT pathology website: Vitamin B12 | North Bristol NHS Trust (

Further advice on reference ranges is given in the Management section below.

Repeat vitamin B12 testing for patients on replacement therapy

Do not send requests for vitamin B12 levels for patients established on long term replacement therapy. This is unnecessary and uninformative.

Algorithm for investigation and management of Vitamin B12 in Primary Care


  • NO - Nitrous oxide
  • MMA - Methylmalonic Acid Test (6) - currently available to request on NBT ICE but not UHBW ICE.
  • IF antibody - Intrinsic Factor antibody


Vitamin B12 assays are performed on automated analysers which test the total amount of vitamin B12 in serum. There is poor correlation between assay systems and may be significant fluctuation in individuals over time - possibly due to fluctuation serum vitamin B12 binding proteins. Testing outside recognised clinical features of vitamin B12 deficiency is likely to increase the number of equivocal test results.

Clinical features of vitamin B12 deficiency are variable but it is also that case that a laboratory finding of reduced B12 levels is not necessarily pathological per se. For example, spuriously low levels are known to occur in myeloma, HIV infection, pregnancy, COCP treatment.
Avoid screening tests for vitamin B12 levels in pregnancy or during COCP use without clinical symptoms or FBC findings suggestive of deficiency.  If tested and low vitamin B12 is found in these situations then assessment of methylmalonic acid (MMA) may help understand whether vitamin B12 deficiency is present.

Prevalence of vitamin B12 deficiency due to pernicious anaemia (PA) estimated to be 0.1% of general European population and 2% those > 60 years. PA occurs in about a quarter of people with autoimmune gastritis. The majority of low levels of vitamin B12 in current UK testing practice are not due to PA.

When to suspect – syndromes of vitamin B12 deficiency:

  • Haematological
    • Macrocytosis (MCV >100fl) / macrocytic anaemia. (In macrocytosis MCV > 115fl is reported to be more specific for vitamin B12/folate deficiency vs other causes). Consider other causes of macrocytosis – see Remedy guidance and appendix in the High Vitamin B12 levels section below.
    • Pancytopenia
  • Neurological syndromes of vitamin B12 deficiency
    • most common neurological findings are symmetric paraesthesia or numbness and gait problems. Symmetrical neuropathy arms > legs;
    • features of spinal cord disease - progressive weakness, ataxia, and paraesthesia: but may not be present early in the disease
    • may include axonal or optic neuropathy and slowed mentation
  • Neuropsychiatric symptoms (including cognitive decline) can be present even in the absence of anaemia or macrocytosis.

It follows that assessment of vitamin B12 levels may be considered if there are symptoms and clinical findings (5):

  • of anaemia – e.g. unexplained fatigue with abnormal blood count (such as unexplained macrocytosis);
  • glossitis;
  • neurological syndromes,
    • paraesthesia (peripheral neuropathy)
    • myelopathy (spinal cord disease: impaired balance and falls linked to sensory ataxia (a sign of spinal cord damage that affects proprioception, impaired gait);
  • disturbed vision (optic atrophy, scotoma);
  • unexplained psychiatric symptoms, including depression anxiety and psychosis;
    problems with memory, such as symptoms related to delirium or dementia,(including as part of dementia screen, noting a casual role of low vitamin B12 is not proven and there is no evidence that replacement impacts upon cognitive function);
  • hyperpigmentation. 

Monitoring of vitamin B12 may be considered in patients with the following as they are at risk of becoming vitamin B12 deficient: 

  • GI conditions that predispose to malabsorption e.g. gastrectomy, bariatric gastric surgery, terminal ilium resection, coeliac disease, Crohn’s disease;
  • vegan/vegetarian dietary restrictions (without vitamin B12 supplements)
  • autoimmune conditions that are at risk of PA, such as autoimmune thyroid disease;
  • genetic predisposition to vitamin B12 deficiency, such as intrinsic factor receptor or transcobalamin II deficiency,
  • long term use of drugs such as metformin, colchicine, PPIs- (NB currently testing is only advised if there is clinical suspicion of deficiency), the anticonvulsants phenobarbital, pregabalin, primidone and topiramate. These mainly cause food-B12 malabsorption.

Special situations

  • Pregnancy: routine vitamin B12 testing should be avoided in pregnancy as results are unreliable (levels naturally decrease in pregnancy). If there is clinical suspicion of deficiency is strong, consider testing but interpret the results with caution. For low levels additional tests may be needed, an alternative approach may be a short course of therapy and reassessment post-pregnancy.
  • Oral contraceptive pill: only test if strong clinical suspicion interpret vitamin B12 results with caution additional tests may be required. Asymptomatic women with mild reduction 145-190ng/l are not likely to need replacement, review diet.

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)

Local implementation of this advice is under discussion and updates will be published here when available. Consider annual testing of vitamin B12 level.

Assessment & Investigations

Investigation of low vitamin B12 levels can be undertaken in primary care and should usually be done before starting treatment (unless severe neurology or severe cytopenia).

Investigations to consider:

  • Consider clinical scenario
  • Dietary review
  • Review of medications (see appendix in the High Vitamin B12 levels section below).
  • Anti-intrinsic factor (IF) antibodies: should only be tested if pernicious anaemia (PA) is suspected - objective clinical/haematological findings of PA - regardless of vitamin B12 level. The test is highly specific for PA but only positive in up to 50-60% people with PA. IF antibodies should not be tested as a reflex to all borderline low serum vitamin B12 results. Currently only 5% of IF antibody tests are positive (internal NBT laboratory data collected October 2023).
  • Antiparietal cell antibodies are seen with gastritis and are not diagnostic of PA, although occur in that condition.
  • Look for other evidence of malabsorption – consider coeliac disease screen.
  • Do not test for H. pylori infection unless the patient has other indications for testing.
  • Plasma methylmalonic acid (MMA) level may help interpret low or borderline vitamin B12 levels by assessing for evidence of metabolic deficiency of vitamin B12 (or folic acid). Homocysteine (tHCy) levels provide similar information but have complicated sample requirements (transport on ice).
  • Response to vitamin replacement - an option for individuals with borderline laboratory values or low levels of uncertain significance, conditions that interfere with measurement (e.g. kidney disease), or discordance between laboratory testing and clinical picture is to give a course of replacement therapy for the vitamin suspected to be deficient (e.g. parenteral vitamin B12 1000 mcg weekly for three weeks).
  • Holotranscobalamin (active B12) assay is not available.
  • Response to vitamin replacement - an option for individuals with borderline laboratory values or low levels of uncertain significance, conditions that interfere with measurement (e.g. kidney disease), or discordance between laboratory testing and clinical picture is to give a course of replacement therapy (folate where relevant) or oral or parenteral vitamin B12.
  • Haematological response can be assessed by FBC and reticulocyte count before and approximately two weeks after supplementation. Both are expected to increase as haematopoiesis responds, and MCV will eventually return to normal, although remains with reticulocytosis.  Measuring FBC parameters is likely to be more accurate than review of general well-being or neurological symptoms since many individuals report the phenomena of more energy following a vitamin B12 infection, even if not deficient.
  • Vitamin B12 administration is extremely safe and inexpensive. Potential problems with using the response to vitamin B12 administration as a diagnostic test include impact of any concomitant interventions that might cause the blood count to respond. Or comorbidities, such as anaemia of chronic disease, may prevent a full reticulocyte response. However, if originally present resolution of hypersegmented neutrophils on the peripheral blood smear is correlated to correction of the deficiency.
  • Testing for intermediates of vitamin B12 and folate metabolism, plasma methylmalonic acid [MMA] and total homocysteine [tHCy], gives further information about functional vitamin B12 (and folate) activity which can be helpful with inconclusive vitamin B12 and/or folate levels, or clinical findings discordant with initial testing values. Plasma MMA can be tested on routine serum samples and requested from primary care at NBT but at UHBW consideration of this test require discussion with Clinical Biochemistry. tHCy testing requires specialist sample handling is reserved for inconclusive vitamin B12 and/or MMA levels, or clinical findings discordant with biochemical results.
  • Gastrin level testing is not specific for PA, has specific sample handling requirements and is not suitable for assessment in the community.

Specialist referral — Vitamin B12 or folate deficiency does not usually require referral for haematology outpatient assessment. Instances for which specialist referral may be useful include:
● Gastroenterology for concern about gastrointestinal conditions that may require additional evaluation and/or treatment.
● Neurology - concern about neurological disorders that may require additional evaluation and/or treatment.
● Haematology - concern about failure of FBC abnormality to respond to vitamin B12 replacement to consider other conditions in the differential diagnosis, such as myelodysplastic syndrome (see appendix in the High Vitamin B12 levels section below, for conditions associated with macrocytosis).

Haematology advice and guidance may be requested if uncertainty regarding management beyond this guidance.


With change in laboratory equipment supplier to Beckman Coulter the reference ranges for vitamin B12 levels are reported according to the table below. Treatment of patients with vitamin B12 levels that are in the borderline range (between 100 and 250) should take into account patient symptoms and clinical findings and should not be based on the test result alone.

Laboratory interpretive comments 

B12 <100

B12 <100ng/L: likely deficiency, commence treatment.

B12 100-180

B12 100-180ng/L: low, possible deficiency. If clinical findings suggest deficiency consider a trial of therapy and assessment of response.

B12 181-250

B12 180-250ng/L : borderline, may indicate deficiency. If strong clinical suspicion suggest discussion with a clinical biochemist or haematologist.

B12 >250

B12 >250ng/L: vitamin B12 deficiency not likely to be present.  


Indeterminate test result and no symptoms or signs of vitamin B12 deficiency

Consider repeating the initial test in 6 months, or sooner if symptoms or signs of deficiency develop.

Indeterminate test result with symptoms or signs of vitamin B12 deficiency

Consider a follow-up test to measure methylmalonic acid (MMA). 
In some scenarios consider treatment, with or without MMA (or while waiting for an MMA result):

  • condition or symptom that may deteriorate rapidly and have a major effect on quality of life (e.g. ataxia or severe anaemia, or pancytopenia)
  • aged 65 or over and have cognitive impairment
  • they have a condition or suspected condition that increases the likelihood of irreversible vitamin B12 deficiency (e.g. autoimmune gastritis, surgery that is likely to lead to irreversible vitamin B12 deficiency (see When to suspect)
  • they are pregnant or breastfeeding.

Measure plasma MMA only where vitamin B12 levels appear discordant with clinical picture. Assay IF antibodies only where causes of vitamin B12 deficiency other than PA are unlikely – do not automatically test IF where the clinical suspicion is low.

See algorithm below


Please also consider the following advice from the original UHB primary care haematology guidelines (2):

  • Assess and perform relevant investigations before treating macrocytic anaemia or neurological symptoms unless there are features that are well established to be associated with vitamin B12 deficiency.
  • Use I.M. hydroxycobalamin for replacement as per BNF or;
  • High dose (1000micrograms daily) oral cyanocobalamin may be considered as an alternative. Approximately 1% is absorbed via gastrointestinal tract and is intrinsic factor independent. N.B. When clinical features of vitamin B12 deficiency are present ONLY parenteral replacement is appropriate.
  • Serum folate levels may be low in vitamin B12 deficiency, whether deficiency is truly present or not. Replacement with folic acid may be given, but delay starting until a day of two after starting vitamin B12 treatment to reduce possible risk of exacerbating neuropathy. e.g. folic acid 1 mg daily for one to two weeks, this regimen may also be used to test for true folate deficiency by looking for response in the FBC and reticulocyte count.
  • A trial of low dose cyanocobalamin 50 micrograms daily can be considered in cases of low vitamin B12 assay results.

High 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 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.  High levels of vitamin B12 may also be seen in CKD, and in nitrous oxide misuse.

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.


Appendix: conditions associated with macrocytosis


Causes in falling frequency.

The first 3 make up about 2/3 of causes.


Alcoholism (the commonest cause of macrocytosis in the UK)

Or other liver disease (often in association with thrombocytopenia).

Vitamin B12 or folate deficiency (may cause pancytopenia if severe)



HARRT (zidovudine, lamivudine, stavudine),

cytotoxics / drugs that interfere with DNA synthesis (azathioprine, MMF, hydroxycarbamide, methotrexate),

others pyrimethamine, trimethoprim, sulfamethoxazole, metformin and nitrous oxide.

Haemolytic anaemia

Due to reticulocytosis.




(Physiological change).

Rare haematological causes

include myelodysplasia, aplastic anaemia.


Some patients have (usually borderline) increased MCVs out with the normal range but no underlying abnormality. 

Consider possibility of storage artifact (MCV rises over time in sample tube).



(1) British Society of Haematology Guidelines for the diagnosis and treatment of cobalamin and folate disorders (2014)

(2) For guidelines and suggested interpretation of test results please see page 15 of the  UHBristol Haematology Guidelines for Primary Care (PDF)

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

(4) Vitamin B12 & folate anaemia - Illnesses & conditions | NHS inform

(5) NICE draft guideline: Vitamin B12 deficiency in over 16s

(6) Methylmalonic Acid (MMA) Test: MedlinePlus Medical Test

MMA a.k.a. methylmalonic acid MMA | North Bristol NHS Trust (

Department of Clinical Biochemistry Test Handbook biochem_handbook_v1.pdf (


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.

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