Pernicious Anaemia Society
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B12 blood test

I am about to have a further blood test to assess my B12 levels. Last time I had it tested I had just had quite a large lunch, but I have recently read that one should fast for 8 - 12 hours before hand as some foods skew the results.

Could someone please explain the reason and foods responsible. I had a private test which came back under 300 and again, I had just had a large lunch before hand.

3 Replies


I've never fasted before a B12 blood test, have them for over 10 years now every year..

Kind regards,



There are some blood tests - namely fasting blood tests - that are supposed to be done after fasting but I think those are generally looking at blood-sugar levels ... and may be some other factors that are about how well your body stores and recycles some nutrients, but list I'm aware of doesn't include B12

Have never heard of any requirement to fast before B12 and its certainly not something I have ever done.


Hi, not sure how my attention was drawn to it, but then googling it, there are several references to fast before the test. Just wondered if it made a difference. It does appear to be an American thing..


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