Thyroid UK
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When to take active B12 test after stopping supplements?

I had a total serum B12 test done privately recently and it came back 314 (150-900); a week later my NHS GP asked for it to be repeated and the result was 400 something low. I have started taking Boots vitamin B complex once a day, but do wonder about getting an active B12 test. I know that I will need to stop taking the B complex tablets before I do, but I was wondering how long to wait before getting tested so that the result isn't skewed?


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If you want to do the Active B12 test then you will need to stop taking the B12/Complex about 2/3 weeks before the test. I think there is advice on the site for the Active B12 test....

You will not have enough B12 in your Complex to make up your shortfall. If you put B12 into the Search Box on the Green Bar you will loads of posts that may be helpful. Look out for hampster1 as her knowledge is EXCELLENT :-)

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This document, written by someone from St Thomas' Hospital in London, gives lots of details about the active B12 test, and it suggests stopping B12 supplements for a month before the test. If this isn't done, then the lab doing the test should be informed :


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