Can I take B12 deficiency test after consuming B12 supplements for 3 weeks

[gotbaya]

Hi, I was wondering if I could go for a b12 test after having taken supplements for 3 weeks daily. If not how long should I wait. Also I would like to check for iron deficiency. So what could be the right kind of test for me?

[fbirder]

Why do you want to take the B12 test?

If you want to see if you can absorb B12 from oral supplements then you should carry on taking the supplements. If your B12 levels are high then it means you can absorb oral B12.

If you want to see if you have a B12 deficiency without the supplements then you'll need to wait at least three months.

[mickeymouse42 in reply to fbirder]

if you are getting B12 injections directly into the blood stream, stopping the injections prior to a test makes sense - I can't see on the PA web site what the recommended interval is.

As regards oral treatments, it's all a bit unclear. The 2018 Cochrane review of oral treatment clinical trials says “The overall quality of the evidence was low or very low”:

cochranelibrary.com/cdsr/do...

When I spoke to a GP about what amounts of oral B12 to take (10mcg, 100mcg or 1000mcg), he said that the body can only inject 10mcg of B12 daily so there's no point in taking 1000mcg. I can't find any evidence for or against this claim (though I'm a bit doubtful).

I also can't find anything that says what the interval between stopping taking oral supplements and doing a follow up test is.

@gotbaya - have you had a benchmark B12 test before taking the supplements?

[fbirder in reply to mickeymouse42]

Blimey! A doc who knew that you can only absorb about 10 mcg at a time (if you do not have PA).