Pernicious Anaemia Society

B12 and Active B12

I've just recently joined the Thyroid community -- I have Hashimoto's and Coeliac -- and was asked to post this query here... Checking back through my B12 tests I can see that I am skipping along the lower 10-20% of the range for B12, and the top 10-20% range for Active B12. I'm in Sydney and testing for Active B12 is standard if B12 is low; see sydpath.stvincents.com.au/t... What is the situation in UK, Canada etc and how are the tests different, and how reliable?

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In the UK most doctors have never heard of an active B12 test and few are keen to order one.

The serum B12 test is notoriously unreliable. It has a large random error (so a true value of 200 might give test results of 160 - 240) and it can suffer from large systematic errors (high levels of anti-IF antibodies, as found in people with PA, can give false-normal or high results - ncbi.nlm.nih.gov/pmc/articl...

The 'normal' range is set so that it catches most people with a deficiency (not all) without flagging to many normal people as deficient.

The serum test is neither accurate or precise blog.minitab.com/blog/real-...

The active B12 test is both more accurate and more precise.

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active B12 has one advantage over serum - that it only looks at the forms of B12 that are bound to proteins that allow them to pass into cells.

However, like serum B12 it is still a measure of what is happening in the blood and not what is happening at the cell level - there are different indirect tests that can help with that namely MMA and homocysteine

Blue_Bee - your results are still within the normal ranges on both even if towards top on one and bottom on the other. 5% of people who are off the bottom of the range will actually be okay.

overlap of symptoms with thyroid problems is going to make evaluating symptoms difficult - so MMA might help

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Wow, this is really helpful. Thank you! Fx

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