What to do next?

Hello, you may have just been diagnosed with B12 deficiency or you may have had this condition for a while. Sometimes our doctors do not tell us all we need to understand, so please use this page as your ‘crash course’ in B12 deficiency.

PLEASE NOTE vitamin B12 injections remain the most efficient and effective treatment for B12 deficiency. Oral supplements are not suitable for everyone.

PLEASE REMEMBER please try not to supplement before testing – this can skew results and may make diagnosis difficult.

Let your doctor (and the lab) know if you have been taking multi-vitamins, B12 supplements, fortified food and drinks and you still have symptoms. You will still require testing.

This page provides a step by step guide but for ease you can click on the headings below to move to a particular point. If you are struggling to achieve a diagnosis and need personalised help please see the Work with me page for more information.

Are you looking for an alternative to social media support groups? Then please consider membership of our private forum.

1. Note symptoms and causes

Check your symptoms or your child’s symptoms. You may want to try our app to test your risk of B12 deficiency.(Please note that

hypothyroidismhyper-thyroidismpyroluria and coeliac disease have overlapping symptoms and can be co-existing conditions).

Note any causes of B12 deficiency that may apply to you.

Have you been exposed to toxic gas or moulds? If so please see B12 the toxins page.

Note anything that relates to you. Your doctor may not understand that certain drugs including metformin and Omeprazole cause B12 deficiency. There are also many drugs which deplete folate.

This page which will help with writing to your doctor and this blog post for further help.

There is a downloadable poster which demonstrates some of the conditions which can occur with low B12 or indeed may be misdiagnosed in place of B12 deficiency. There are hyperlinks to journals behind each image.

2. Tests to diagnose B12 deficiency

Ask your doctor to test serum B12, folate (B9), ferritin (iron storage), and a full blood count (FBC).

Although not routinely tested on the NHS, MMA (Methylmalonic acid) and Homocysteine (tHCY) are good indicators of B12 deficiency.

The importance of testing ferritin and folate cannot be stressed enough, folate and B12 need each other and a healthy level of ferritin (iron stores) is essential. These should be fasting tests so ask for an early appointment.

Sometimes doctors are reluctant to carry out these tests, however they can be done privately via home test kits, through online labs or private hospitals.Please see more information on testing.

3. Obtaining a copy of your results

Once your results are back it is very important to obtain a copy.

Unfortunately many of us are incorrectly told that our results are ‘normal’ when in fact this is not the case. You are legally entitled to copies of your results but some practices may charge.

4. Your results and what they mean

Learn to interpret your results.

If you are symptomatic your serum B12 level could still show as ‘within range’ this test is known to be inaccurate. Please see the NEQAS B12 alert which explains about ‘false normal’ results and warns not to delay treatment. “In the event of any discordance between clinical findings of B12 deficiency and a normal B12 laboratory result, then treatment should not be delayed”.

It is important to understand that the B12 serum test records both active B12 which can be used by the body and inactive B12 which can’t. The test may record as much as 80% of inactive B12 otherwise known as B12 analogues.

Read here from the NHS website – www.nhs.uk/Conditions/Anaemia-vitamin-B12-and-folate-deficiency/Pages/Diagnosis.aspx

‘A particular drawback of testing vitamin B12 levels is that the current widely-used blood test only measures the total amount of vitamin B12 in your blood. This means it measures forms of vitamin B12 that are “active” and can be used by your body, as well as the “inactive” forms, which can’t. If a significant amount of the vitamin B12 in your blood is “inactive”, a blood test may show that you have normal B12 levels, even though your body cannot use much of it. There are some types of blood test that may help determine if the vitamin B12 in your blood can be used by your body, but these are not yet widely available.’

This Clinical Review from the BMJ on B12 deficiency states:

“There is no ideal test to define deficiency and therefore the clinical condition of patients is of the utmost importance.”


“If the clinical features suggest deficiency then it is important to treat patients to avoid neurological impairment even if there may be discordance between the results and clinical features”

A ‘normal’ serum B12 level can indicate a Functional B12 deficiencythis is a genetic  condition which your doctor should investigate;


‘Some people can experience problems related to a vitamin B12 deficiency, despite appearing to have normal levels of vitamin B12 in their blood. This can occur due to a problem known as functional vitamin B12 deficiency – where there is a problem with the proteins that help transport vitamin B12 between cells. This results in neurological complications involving the spinal cord’.


‘We describe a case of functional vitamin B12 deficiency where the repeated measurement of a serum B12 level within the normal range led to delay in the diagnosis of subacute combined degeneration of the spinal cord, and possibly permanent neurological damage as a result….’

Symptomatic patients may be suffering from B12 deficiency caused by parasites or infections such as SIBO, this can lead to misdiagnosis since serum B12 levels will often be within range despite a possible severe deficiency.

Please note that if you suffer psychiatric symptoms of B12 deficiency, they too are reversible with correct B12 treatment. Psychiatric symptoms can manifest at higher levels than the lower reference ranges of the B12 serum test. In these cases it would be entirely appropriate for your doctor to carry out a therapeutic trial of B12 injections to confirm a deficiency. Folate deficiency can also have a huge impact on your mental health.

An extremely high B12 level without supplementation requires investigation.

These particular test results from an FBC (Full blood count) are important in B12 deficiency:

  • Ferritin
  • Folate
  • Red cell folate
  • MCV
  • MCH
  • MCHC
  • RDW

Read more about these on the testing page.

It is important to remember that B12 deficiency cannot be ruled out in the absence of anaemia and / or high MCV.

5. Your diagnosis of B12 deficiency

If you have results which confirm a deficiency, do not accept cyanocobalamin tablets unless you know that your deficiency is due to a dietary lack of B12. Remember B12 is only available from animal products, fortified foods and supplements.

Oral supplements may effect serum levels but may not repair damage, deterioration may continue undetected if the symptoms of the patient are ignored whilst blood levels are relied upon. This case of SACD went undetected in a 22 year old who had been given oral supplements which had ‘corrected’ her serum level.

This BMJ article discusses how ineffective oral B12 is, stating; ‘……a minority of patients respond clinically to oral therapy’.  The latest BMJ article from November 2023 will be of great help to your doctor.

A deficiency, even if caused through a vegan or vegetarian diet, should still be treated by injections in the first instance, in order to build levels fast.

Urge your family members to check their symptoms and take a look at the Causes page too, this deficiency could also be affecting your loved ones.

6. Correct treatment - loading doses

You should be given loading doses by injection. (Six injections over 2 weeks.) Please note: Oral B12 tablets should only be prescribed f the deficiency is caused by a proven dietary lack.

If you have neurological symptoms then your doctor must treat you as per NICE CKS Summary and BNF (British National Formulary) guidelines, these both state that you must stay on loading dose frequency (every other day injections) until symptoms stop improving. Each practice has a copy of The BNF book and the Guidelines are found at (9.1.2.). Please also see NICE Guidance for the over 16’s March 2024.

There are many reasons why people cannot cope on quarterly or even monthly injections. This frequency was arrived at through GP audits and not clinical evidence!

You may have to remind your doctor that there is no known toxicity of hydroxocobalamin and that it is used in huge quantities to treat cyanide poisoning.

Once treatment starts you may notice certain reactions (for example spots) during or soon after the loading doses.

Once B12 treatment with injections has commenced B12 levels do not require re-testing unless you are not improving. Your serum level does not give any indication of what is happening at a cellular level. NICE stateMeasuring cobalamin levels is unhelpful as levels increase with treatment regardless of how effective it is, and retesting is not usually required. 

7. Maintenance doses

A UK doctor should use the guidelines above, but sometimes this doesn’t happen. Nerve damage takes a long time to heal that is why there is no limit on the administration of B12 injections in those suffering neurological symptoms. Unfortunately people are often given a loading dose and are then made to wait 3 months before another B12 will be given. This is not adequate for many. Four injections per year will not heal nerve damage, they will keep you alive but deterioration will continue. 

I started a petition which asks for us to be allowed to buy injectable B12 from pharmacies in the UK so that people can be involved in their own care.

We have a page which will help with Writing to your doctor but If you would like personalised help with any aspect of accessing correct treatment please visit the Work with me page.

8. Self injection

Ask your doctor / nurse to teach you how to self inject. This will save you and your practice time and money, if you have neurological symptoms you could be injecting every other day for months. Please see an injection guide here.

9. Treatment is for life

If you are B12 deficient and it is NOT due to a dietary lack of B12 or due to a parasite or other curable forms, you will require injections for life.

In these cases, please ask your doctor to write this in your notes. Some patients may experience a complete withdrawal of treatment when changing doctors.

10. Folate (B9) and B12

If your results show that you are low in folate (B9) this will require supplementation, Vitamin B12 and folate need each other!

Your serum folate level should be at the upper end of the range and will require monitoring periodically. Please note: folic acid is widely prescribed but it may be that you require supplementation of the forms of folate more recognisable to the body – methylfolate and folinic acid.

11. Iron anaemia

Please see the Case study on Ellen for more information.

12. B Complex

It is also wise to take a good vitamin B complex in addition to your B12 injection as all B vitamins need each other to work properly. Supplementing one in isolation can cause an imbalance in others. 

If you can increase your intake of B6 from food then there is no risk of toxicity, however some people have experienced side effects such as neuropathy from daily very high dose vitamin B6 when taken for long periods.

Please note, the folate contained in B complexes and multivitamins is commonly folic acid and this may not be the best form for you. Please see point 10 above.

13. Potassium

During early intensive B12 treatment some people experience a drop in potassium levels. Low potassium hypokalemia can cause symptoms such as severe headaches, palpitations and dehydration. Your doctor should keep an eye on this and you can help yourself by eating potassium rich foods

14 Magnesium

Magnesium is by far the most important mineral in the body it needs replacement every day and is vital for our methylation process. 

15. 'Within range' or 'Normal' results

If you doctor feels that you are not B12 deficient based on ‘within range’ results you must push for further testsIf you have neurological symptoms and a doctor who is non compliant you must assert yourself or take someone with you who can support you. Using the Writing to your doctor page will help you to educate your doctor and you can also access personalised help for tailored support with this.

The links at Point 4 above will help your doctor to understand the inaccuracy of the B12 serum test. 

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Writing to your Doctor

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