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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 it can 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 may be denied the treatment you need.


The symptoms of vitamin B12 deficiency can be difficult to recognise as they can be similar to those of a variety of other conditions. To add to this difficulty, the training most health professionals generally receive on nutrients and deficiencies is minimal, therefore many misconceptions of B12 deficiency exist within the healthcare industry. An example of this is that many doctors think that unless their patient has a form of anaemia that causes abnormally sized red blood cells, that they cannot have a B12 deficiency. However this is untrue, as research has shown that many signs, including neurological symptoms, commonly precede blood manifestations. 

To further complicate diagnosis, there is currently no gold standard test for B12 deficiency. This means that tests showing normal levels of B12 in the body are not always reliable. And although there are several testing options available, some proving more sensitive than others, our doctors tend to only use the standard blood serum test, which measures the total B12 levels in your blood and is known to be the oldest and most inaccurate of all tests available. This is because the results of this test are made up of both an “active” form of B12 that your body can potentially use, and an “inactive” form that your body cannot use. So, if you have a low level of the “active” B12 in your blood, and a higher level of “inactive” B12, it can cause your total B12 level to fall within reference ranges, therefore your deficiency will likely be left undiagnosed, or even misdiagnosed as something else (Please see our page on COMMON MISDIAGNOSES).

To compound the inaccuracy of the blood serum test, it is also the case that reference ranges, set to guide diagnosis from blood results, are not only generally set too low, but they are also allowed to be individually set by each NHS health board/CCG resulting in a postcode lottery effect, where a patient can be tested in one area of the country and be told that they are within reference range, therefore left untreated, but then be tested again in another part of the country only to find that they are below reference range there, so treated for deficiency, and vice versa. These low set reference ranges are allowing too many patients to fall through the net, and the individually set reference ranges by NHS area create worrying inconsistency in the diagnosis of vitamin B12 deficiency across the UK.

As for the other types of test for B12 status, namely Holotranscobalamin (Active B12), Homocysteine and Methylmalonic Acid, they are not always readily available to doctors, many of whom can often be unfamiliar with these tests, therefore access can be difficult. Further information on all tests is shown below.

So unfortunately the road to diagnosis can sometimes take a considerable length of time (and often unnecessary tests, scans and referrals) before a correct diagnosis is achieved.

Warning!  Some doctors will look to recheck your serum B12 level after B12 therapy has begun. This is a pointless exercise as the therapy will raise your blood levels and/or correct any enlarged blood cells without necessarily correcting any other symptoms. This will likely result in your B12 therapy being stopped without your deficiency being fully addressed. This can potentially cause irreversible neurological damage!

Do not allow testing of your B12 levels after any form of B12 therapy has begun. 


1st Line Testing

If your symptoms fit with those of vitamin B12 deficiency, the first line of blood investigation should be as follows:

  • Full Blood Count (FBC)

  • Serum B12

  • Serum Folate

  • Ferritin

  • Thyroid

It is also highly recommended that your vitamin D (25 (OH) vitamin D) status is also checked at this stage, as it is not uncommon to be deficient in both vitamin B12 and vitamin D, since they share a common receptor site in the ileal section of the digestive tract known as cubilin.

2nd Line Testing

If your 1st line blood tests are not conclusive, these 2nd line blood/urine tests can be very helpful to the diagnostic process:

  • Serum Active B12 (holo TC)

  • Serum Methylmalonic Acid (MMA)

  • Urinary MMA

  • Serum Total Homocysteine

  • Intrinsic Factor Antibodies (GIFA)

  • Parietal Cell Antibodies (GPC)

Please remember that since there is no gold standard test for vitamin B12 deficiency, that testing negative or being "within range" for any of these tests does NOT rule out a vitamin B12 deficiency.

Before your blood test

The Do's

The Don'ts





Whilst it is not essential for testing vitamin B12, it is likely that your Iron levels (ferritin - iron stores) will be included in your initial tests, and it is advisable to fast for 12 hours prior to having these blood tests taken. For further information on this please click HERE to go to the NHS website



The symptoms of B12 deficiency can be so varied, and appear in any area or system of your body. Because every person has their own individual experience of the condition, ranging from minimal irritations to extensive debilitating symptoms, it can be difficult for your doctor to fully understand what you are experiencing and the impact that it has on you. Therefore it can be very helpful for both you and your doctor to have a list of your symptoms from which you can build a full picture together, enabling a more effective diagnosis. 

You need to be CLEAR of any any supplements containing vitamin B12, and/or foods and drinks with unnatural levels of B12, such as those fortified with or containing concentrated levels of B12 for AT LEAST 4 MONTHS BEFORE TESTING SERUM B12.


This is because it is possible for unusable B12 to remain in the blood for this time (some studies say up to 6 months), and even though your body cannot use it, your blood test will be skewed because of it, and this will make diagnosis difficult.


  • All foods, drinks fortified with B12. Which include cereals, soya drinks, Marmite and other foods (check the labels)

  • B12 injections/supplements/sublingual's/patches

  • Energy drinks such as Red Bull, Juice Plus and some protein and slimming drinks

  • Multivitamins such as Wellwoman, Menopace, Centrum

  • Collagen powders Wheatgrass, green powders, spirulina, nori, miso as they are B12 analogues (SEE OUR SECTION ON B12 ANALOGUES FOR FURTHER INFORMATION)

Supplements & Fortified Foods

After your blood test

The Do's

The Don'ts





Since, ultimately, we are responsible for our own health, it is a good idea to become more familiar with our own test results. And as a charity with a large support group, we are increasingly finding that many of our members who have been told that their results were "normal", but then requested a copy of their blood test results, go on to find that there were potential, or even clear signs of deficiency that were missed by the lab and/or doctor.

We offer help with understanding your blood/urine test results for vitamin B12 and cofactor deficiencies on our Facebook support group Vitamin B12 Wake Up which is a private, closed group. Everyone is welcome to apply to join this group, where all members have access to extensive files on all aspects of vitamin B12 deficiency, and our experienced Admin and Moderator team (including health professionals) are happy to support, assist and advise.

It is important to be aware that you are fully entitled to request a copy of any of your health records, and that your health care providers are legally bound to supply you with them (some clinics may charge an administration fee for these, but most don't).

Because one of vitamin B12's key roles in the body is to maintain the health of our nervous system, an untreated or undertreated deficiency can cause irreversible neurological damage. Therefore it is essential that potential symptoms of this condition are not left unexplained or misdiagnosed as some other condition, therefore left untreated and without the necessary life-saving B12 therapy.

It is also the case that those lucky enough to be diagnosed correctly are often undertreated, with maintenance B12 injections only being administered every 8 to 12 weeks, even though they are experiencing neurological symptoms.

The guidelines clearly state that B12 deficient patients with neurological symptoms should be treated with intramuscular Hydroxocobalamin, and "should receive 1000 μg i.m. on alternate days until there is no further improvement" (see British National Formulary and British Journal of Haematology).

We can offer help with getting the right treatment for you as an individual on our Facebook support group Vitamin B12 Wake Up.


Full Blood Count (FBC)

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...

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...

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...


Thyroid Function

Holotranscobalamin (Active B12)

Ferritin is a protein that stores iron which is necessary to produce healthy red blood cells that will carry oxygen around your body. Vitamin B12 works with iron to ensure the formation of normal sized and shaped red blood cells. Blood concentrations of ferritin reflect how much iron is stored in the body.

Low levels of ferritin can lead to...

The symptoms of hypothyroidism can often be similar to those of vitamin B12 deficiency e.g. tiredness/fatigue. It is also the case that there is a 40%-52% prevalence of B12 deficiency in hypothyroid patients [1,2]. For these reasons, it is advisable that your doctor checks for hypothyroidism when a B12 deficiency is suspected and vice versa...

Holotranscobalamin (holoTC) test commonly known as "Active B12" is a blood test that measures the amount of active vitamin B12 in your blood. Unlike the B12 Serum Test which measures your total B12 (active + inactive), the holoTC test only measures the active form of vitamin B12 that is useable by your body. 

Although this is regarded as a more accurate measurement of your B12 levels...

Methylmalonic Acid (MMA)

Methylmalonic Acid (MMA) is a compound produced by the body during the metabolism of amino acids. It is usually produced in very small amounts, however it relies on sufficient levels of vitamin B12 to act as a coenzyme in this process, so when your B12 is too low, your body can begin to produce higher than normal levels of MMA.

Blood tests showing normal levels of...

Homocysteine (tHcy)

Homocysteine (Hcy) is present in small amounts in the body's cells. It is an amino acid that gets converted by the body into other essential products required for normal function.

Vitamins B12, B9 (folate) and B6 are essential nutrients required to metabolize Hcy effectively, so lower levels of any of these B vitamins can cause higher levels...

Parietal Cell & Intrinsic Factor Antibodies

Specialist cells in the stomach wall called

parietal cells, produce a protein known as intrinsic factor (IF) which binds to the vitamin B12 from our food, creating a complex that enables the absorption of vitamin B12 in the terminal ileum area of the small intestine.


When your body produces autoimmune antibodies against parietal cells and/or IF your body cannot form the IF/B12...

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