The symptoms of vitamin B12 deficiency are so similar to those of a variety of other conditions that it can take some considerable time (and often unnecessary tests, scans and referrals) before a correct diagnosis is achieved. Your doctor will take blood samples and if your red blood cells are enlarged, this should alert him to a possible B12 deficiency. Alcohol abuse also affects the red blood cells so don’t be alarmed if he asks about your alcohol intake!


Problem – you can be deficient and still have normal red blood cells.


Next step is to take another blood sample to check the level of B12 in your bloodstream. Your doctor will usually base his diagnosis on the figure which comes back. Problem – you can have a normal reading and still be deficient!  What is considered a low reading varies from one area to another in the UK and can also vary greatly from country to country.


Problem – you can be deficient in Edinburgh but normal in London! Many doctors are reluctant to treat if the reading is just within normal range, completely disregarding any symptoms the patient has.


Warning!  If you suspect you are B12 deficient we strongly advise you DO NOT take any B12 supplements before you have had a blood test. It is only natural to try some vitamin supplements to see if they make you feel better but in the case of B12 they will elevate your blood levels without giving long term benefit if you are deficient. A raised blood level is likely to be enough for a doctor to consider you are not deficient and you will be denied the treatment you need.


Full Blood Count


Serum B12 (Total B12)

Many health professionals will look for Macrocytosis (enlarged blood cells and a possible indicator of B12 deficiency) within the full blood count before considering testing for b12 deficiency. However, there are factors that will mask macrocytosis, such as a good folate level or a low iron level.


Macrocytosis is not always present in b12 deficiency regardless of folate and iron levels.


Macocytosis is end stage b12 deficiency, therefore symptoms can be present long before any haematological abnormalities are present.

Other blood indicators of a possible b12 deficiency can include low red cell count, low/high platelets, high MCV, high MCH,
high MCHC, low white blood cells, abnormal liver count, low ferritin.

Folate (vitamin B9) is a water soluble vitamin, and is more commonly known in it's synthetic form folic acid.

It is an essential cofactor of vitamin B12 and without sufficient levels of it, your body cannot utilise its B12 effectively.

Low levels of folate can cause red blood cells to become enlarged (megaloblastic anaemia/macrocytosis), which can also be a marker of B12 deficiency. However not everyone with B12 deficiency will develop enlarged blood cells.

When receiving B12 therapy (supplements), your folate levels must be >15ug/L for the B12 to be optimised (see TREATMENT page for further information).

Many women take folic acid supplements in their early stages of pregnancy, and/or when they are planning for a baby. This is because folate is known for its helpful effects in reducing the risks of neural tube defects. However, B12 deficiencies can also cause such birth defects [1], and an undiagnosed B12 deficiency can be masked by correcting folate levels. So being aware of your B12 levels during pregnancy is very helpful.

Reference ranges for folate vary marginally between labs, depending on the types of machinery used for testing. But for adults in the UK they are generally around the following:

3 - 20 ug/L

Please note that it is possible to be symptomatic even at the lower end of this range.

[1] https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/complications/

Although the B12 serum test is widely known to be the most inaccurate method of measuring a person’s vitamin B12 status [1], it is still the go-to test for most health professionals when looking to test a patient for a B12 deficiency. This is for various reasons, but mainly because it’s the oldest of the tests and most widely available, so is the one that's best known to most doctors, it’s inexpensive to do, and also because most doctors are unaware of the alternatives and their superior efficacy.

Unfortunately the B12 serum test measures both active forms and inactive forms of the vitamin, and given that a large majority can be in the latter form, therefore cannot be utilised in the metabolism, this test is very unreliable and allows too many people with B12 deficiency to slip through the net.

It is also the case that the reference ranges applied to the B12 serum test vary greatly from one area of the UK to the next, thus creating concerning inconsistencies that mean a patient tested in Edinburgh may fall “within range”, but be deficient if tested in London. Once again causing B12 deficient patients to either remain undiagnosed or even become misdiagnosed.

[1] https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/diagnosis/

Holotranscobalamin (Active B12)

Methylmalonic Acid (MMA)

Homocysteine (tHcy)

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Vitamin D

Thyroid Function

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Full Iron Panel

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Vitamin D

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© 2020 by RUORRA in support of The B12 Society

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The B12 Society is a Scottish Registered Charity, no. SC046066.

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