Pernicious Anaemia Society
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Has anyone had experience of having Active b12/MMA test after taking antibiotics please?

Hi, apologies if you've read this on Thyroid site, typed it in earlier thinking I was on B 12 site, so here goes again!

I've just finished taking a week of Amoxicillin, which didn't work, then Co-amoxiclav 500mg/125 mg for a week for recurring sinus and inner ear infections. I've just been given a referral to have the Active b12 test and would like to push on, but read in the latter meds that red blood cell and white blood cell results, glucose and liver results can be affected.

I've checked and they think Active b12 result wouldn't be affected, but if I needed MMA this possibly could be, but don't state how long to wait. I've asked, but just wondering if anyone has any ideas or experience of this please and can offer some words of wisdom! Have waited quite a while to get this sorted, but don't want to pay and get the wrong results!

Any ideas greatly appreciated thanks :)

6 Replies

I believe that the test for MMA used to be microbiological, which would suffer interference from antibiotics.

But nowadays the test is done using gas chromatography - mass spectrometry (GC/MS - what I used to do at work). This assay will not be affected by antibiotics.

Just for a bit of name-dropping. Our company won a Queen's Award for developing amoxicillin/clavulanate and I got to go to Buck House to meet her Maj. But that was nowhere near as exciting as was chatting to the team who won an award for the Giotto spacecraft.


Hi Many thanks for taking the time to reply and for such interesting and helpful information. I've just been reading through some of Sally Pachoks book today and she mentions that MMA results can be normal in b12 deficient patients receiving antibiotics, which can eradicate the intestinal flora needed to synthesise propionic acid. Can I ask if this is what you mean when mentioning the two different methods of testing or is this a different issue? As a non medical person I would assume that the MMA level is lowered and whatever way it is tested it is lower than it should be due to antibiotics, but are you saying by using a different method it can somehow not affect the results?

I hope that makes sense, I know what I want to say, but the fog is setting in!

Such interesting work, I hope her mag. was impressed!

Thanks so much once again :)


While some propionic acid is formed by gut bacteria, and so may be affected by antibiotics, it is also produced by the body as the end product of the breakdown of odd-carbon fatty acids.

I presume Ms Patchok's thinking is that a lack of propanoate formed in the gut might means less MMA is produced. And that may be the case.

The old test measured MMA using bacteria. So any antibiotic would kill off those bacteria, ruining the test results.

The new GC/MS test wouldn't be affected. However, if the amount of MMA in the body was reduced due to antibiotics then it would give an accurate (i.e, low) result.


Hi, thanks so much for your help, sorry for my slow reply, can't shake off this sinus and ear infection/ temp so on more antibiotics now, just what I didn't want when waiting to get these tests sorted!

Thanks for explaining it further, I understand what you're saying, but can I pick your brains again and ask whether you feel the active b12 test would be affected by my having had an infection and these 3 courses of antibiotics please? I'd love to hear your opinion...thanks again


I'm not sure what type of assay they might use for holotranscobalamin (active B12 ot HoloTC). The recent Nice document describes a cheap immunoassy and mentions an older, more expensive, immunoassay -

Nether of these assays should suffer interference by the presence of antibiotics. Immunoassay is a very specific technique, where they create an antibody that will bind to the molecule being measured and nothing else (well, unless it's a very similar).


Thanks very much once again, will read through that link...:)


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