Pernicious Anaemia Society

Blood Test for B12

Hi, I recently had a blood test fir my B12 and folat which both came back as normal (419 and 5.2). However, I am still having symptoms, mainly bad pins and needles in my hands and very bad in my feet, to the point where I can't walk sometimes. Could this be related to my hypothyroidism and not B12?

Also does anyone have any pain killer suggestions as my doctor just said paracetamol which doesn't even begin to touch it.


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Also, I have been told that anything under 500 for B12 is low but my doctor disagrees?


Are you supplementing with folic acid Serendipity_28 ?


No I'm not.. should I be?

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Folate "gets used up" and is essential to process the B12. Has your Folate level been checked recently?


Yeah, I was 5.2


You are right to question whether the test result is normal Serendipity, as there is no reliable test (see various research and guidelines in pinned posts on the R/H side). It is more important to consider symptoms as deficiencies begin to appear in the spinal fluid below 550 pg/ml.

The symptoms you describe are neurological signs of B12 deficiency and should be treated urgently with B12 injections according to BNF guidelines until no further improvement to avoid the risk of permanent damage.

The research document below shows the link with Autoimmune Thyroid Disease and how autoimmunity progresses to damage the gastric mucosa that makes it more difficult to absorb B12 and other essential nutrients:

"PA is associated with atrophic body gastritis (ABG), whose diagnosis is based on histological confirmation of gastric body atrophy. Serological markers that suggest oxyntic mucosa damage are increased fasting gastrin and decreased pepsinogen I. Without performing Schilling’s test, intrinsic factor deficiency may not be proven, and intrinsic factor and parietal cell antibodies are useful surrogate markers of PA, with 73% sensitivity and 100% specificity. PA is mainly considered a disease of the elderly, but younger patients represent about 15% of patients."

"PA patients may seek medical advice due to symptoms related to anemia, such as weakness and asthenia. Less commonly, the disease is suspected to be caused by dyspepsia. PA is frequently associated with autoimmune thyroid disease (40%) and other autoimmune disorders, such as diabetes mellitus (10%), as part of the autoimmune polyendocrine syndrome.

PA is the end-stage of Atrophic Body Gastritis. Long-standing Helicobacter pylori infection probably plays a role in many patients with PA, in whom the active infectious process has been gradually replaced by an autoimmune disease that terminates in a burned-out infection and the irreversible destruction of the gastric body mucosa. Human leucocyte antigen-DR genotypes suggest a role for genetic susceptibility in PA.

PA patients should be managed by cobalamin replacement treatment and monitoring for onset of iron deficiency."

I hope this and the guidelines will help convince your GP to trial injections without delay.


Hi, thanks. That seem really helpful and hopefully it's well 😊


Serum B12 isn't a gold standard test - normal ranges are set by labs that balance the risk of identifying people who aren't B12 deficient as deficient against the risk of missing people who are B12 deficient. Unfortunately the general levels are such that whilst they might capture 5-10% of people who aren't actually B12 deficient they will also miss 25% + of people who are deficient which is why evaluating on symptoms is so important.

It is not correct to say that anything under 500 is deficient. It is correct to say that significant numbers of people can be B12 deficient at levels up to 500 and that evaluation needs to take into account symptoms ... though also true that you need to know which units you are talking about ... and I personally can never remember which the 500 actually goes with ... as there are two units that can be used to measure serum B12.

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Units for measuring B12 are:

133 - 675 pmol/L (picomole per litre)

200 - 900 pg/ml (picogram per litre)

180 - 914 ng/L (nanograms per litre)

Ranges are thereabouts due to different lab machines, machine calibration fluctuations and local 'determinations' of population statistical norms (for want of a better way of putting it). Understand variations can be quite wide - normal reference range for my serum B12 was quoted as 240 - 900 ng/L.

Believe units used may be Country specific, but not sure who uses what where 😖.

The 500 figure is posited in relation to the pg/ml reference range (Pacholok quotes a figure of 550pg/ml, though she is talking of levels of B12 in cerebral spinal fluid (CSF) 'Could It Be B12...p11)


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thanks Foggyme

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With me symptomatic does this mean I am deficient? I believe it was picogram per litre serum level


if you are symptomatic then that points to B12 but there is a huge overlap with other problems including thyroid.

Serum B12 isn't a definitive test - there are 4 tests that can be used but all require interpretation and looking at symptoms - Serum B12, active B12, MMA and homocysteine. MMA and homocysteine can both be affected by factors beyond B12 so aren't first line tests - and which tests you do is a question of balancing cost and how clear clinical presentation makes things. One thing GPs don't realise is that there is so much variation from person to person that the levels set as normal are averages on a huge amount of variation which means that the results alone can pick up some people who aren't deficient as deficient (5-10% on the case of serum B12) but will also miss some who are deficient but fall into the normal range (25%+). That last bit is the frightening bit. active B12 is a bit better but still suffers from variations.


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