Share on Twitter
Share on Facebook

B12 Testing

Please be aware that taking any B12 supplements at all prior to being tested could skew your results and this may cause you to remain undiagnosed. Even if you cannot absorb B12 orally your serum test could record a 'within range' result for a few months. 

PLEASE TRY NOT TO SELF TREAT before testing! If you have, please make sure your doctor understands this and that they let the testing lab know too.

Folate (B9) and ferritin (iron storage) levels should be checked alongside B12, you may not be low in these but B12 deficient patients often are.

Diagnostic Tests - please note symptomatic children often show as within range on a serum B12 test. They may require ALL tests to establish a deficiency.

We have developed an app to help determine your risk of B12 deficiency.

You can view a 90 minute broadcast on B12 deficiency with me, from the Academy of Physical Medicine here. There is a small charge. See a small clip here


  • The most common test is serum B12 - The reference range can be set as low as <110 - 900 ng/l in some parts of the UK. This is a problem as the test often misses desperately deficient people.
    The serum B12 test, records all B12 in the blood, active and inactive (B12 Analogues), it does not record what is happening at cellular level.
    The body cannot access inactive B12 and this can represent as much as 80% of the level showing in serum.
    There are documented problems with the accuracy of this test, however many health professionals are not aware of this. Click here to read the NEQAS  B12 alert. 

  • Please be aware that The active B12 test (also known as Holotranscobalamin or holoTC) can also miss B12 deficient patients. Please see This Clinical Review from the BMJ on B12 deficiency which states: 
    "There is no ideal test to define deficiency and therefore the clinical condition of patients is of the utmost importance."

  • Serum MMA - (methylmalonic acid) is available on the NHS although not routinely used, it is however a very useful indicator of B12 deficiency. It is widely available through private labs.

  • Urinary MMA - This test is only available privately in the UK but can be ordered directly without referral, from the US. Click here to learn more from Dr Eric Norman's website.

  • Homocysteine - In the UK this test is not routinely used but can be carried out at your GP practice or at your local hospital if requested by your doctor. This test is widely available through private labs. Homocysteine Is an amino acid produced by the chemical conversion of methionine. It can can rise to a toxic level if B12, B6, folate (B9), B2 and magnesium are low. It has been thoroughly documented  that even moderately elevated homocysteine levels are a strong risk factor for  cardiovascular disease, stoke, and neuro-degenerative diseases including  dementia and Alzheimer’s.

  • MTHFR - methylenetetrahydrofolate reductase (gene mutation) for more information on methylation please click here 

The following antibody tests are used to determine if the reason for B12 deficiency is Autoimmune Pernicious Anaemia, however they can be unreliable due to low sensitivity. It is also important to remember that there are many causes for B12 deficiency and PA is just one.

  • Gastric Intrinsic Factor Antibodies. (GIFA)

  • Gastric Parietal Cell Antibodies. (GPCA)

Adding B12, and folate tests to a 'full blood count' would help doctors to diagnose a B12 deficiency much earlier than at present.  Please read the in depth key information on optimum levels written and compiled by Pat Kornic.

The following results from a 'Full blood count' are important in B12 deficiency:


It is important to remember that B12 deficiency cannot be ruled out in the absence of anaemia and / or high MCV. Click here for more information compiled by @b12unme.

  • Your MCV level (mean corpuscular volume) which is tested as part of full blood count will also be key in determining macrocytosis - (large red blood cells). Please note absence of high MCV does not exclude B12 deficiency. Click here for more information.
If you value this website, consider donating. Donations support the free information provided on and its blog, which help those with B12 deficiency world wide.

Enter email address to sign up for news and events.




    News and events