Pernicious Anaemia Society
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Homocysteine & MMA Tests - Does it matter when I had my last injection?

I am, completely unexpectedly, being given MMA & Homocysteine tests for possible Functional B12 Deficiency. I've just had a B12 injection so I arranged to have the tests in a fortnight's time so that I'm not full to the brim with B12! However, I don't know if I'm putting myself at some disadvantage with this quite close timeframe. Should I really arrange for the tests to be done immediately before my next injection (I have them every 4 weeks) so that I'm at my lowest ebb?

I know that with Functional Deficiency the whole problem is you are not using the B12 at a cellular level, but I obviously do use some of it as I always have less problems for the first 2-3 weeks after an injection. So if my Functional Deficiency is a 'milder' case (non-genetic, I'm guessing) would I really be better to get the samples taken right before my next injection, or will this really not matter? Is it a case that if I have the deficiency my MMA & Homocysteine will be elevated no matter when I've had an injection?

This is very anxiety-producing because when you are being given special one-off tests they are exactly that - you don't get another shot at them. I am desperate not to screw this up. So anyone who can throw some light on this, or give me good reliable advice on what to do here, would be welcomed with virtual hugs and virtual chocolate. Many thanks!

6 Replies

I'd always believed that b12 begins to lower homocysteine immediately and if you wanted a usable homocysteine or mma result you'd need to be off all b12 supplementing for 4 months.

However if the test is to identify a functional deficiency then I guess that might not apply if you're not actually able to use the b12 you injected.

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Thanks, Steap, it is just to check for Functional Deficiency so if the tests come back as normal that will be fine and dandy, if embarrassing!


if you are okay for a few weeks after injections then that would imply that is a period when you aren't deficient at the cell level but its after this that not enough is getting through and you are functionally deficient - so would be best to go for doing the tests just before a maintenance shot.

Functional B12 deficiency does respond to raising B12 levels in serum but establishing exactly how raised the levels need to be is, as far as I am aware, impossible at the moment/not cost effective. My simplistic way of looking at it is like building a dam but still needing water downstream - which means that there has to be enough water behind the dam for stuff to trickle over the top.


Thanks, Gambit, I've taken your advice and moved the appointment to 4 days before my next injection, If I'm not showing any functional deficiency 4 days beforehand I'm guessing I don't really have the problem at all!


Might be worth holding off on the b12 until you've got the results and decided on how to use them or you be waiting another three months.


I get 4-weekly injections currently, Steap, so I'm waiting till 4 days before my next injection and then having the tests then. If they come back normal then I'm scuppered - I don't think they would restest unless I turned up with paralysis in both legs. If you're meaning I should go without my injections for a few months before I test, I don't think I could bear to do that. The reason I'm having this done is my Trigeminal Neuralgia is threatening to come back. If I stopped the b12 and it did come back that might be a good scientific experiment, but it would be a hellish thing to do to myself.

Anyway, given my doctors past record I doubt it if even that would convince them my TN is a B12 issue!


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