Hi, I have had a history of b12 def in pregnancy 23 years ago. My levels were at 700 when tasted in 2011 without having had a b12 injection for 5 years although I had had some oral b12 supplements during that period. In September my levels were rechecked due to neuro symptoms which I have been experiencing increasingly over that period. Serum b12 was at 319. After some discussion GP agreeed to giving me alternate day injections which I have been receiving since November. He now says he needs to get a clear diagnosis for these to continue despite significant improvements in my symptoms eg I can walk better and am far less dizzy. I still have a long way to go.
My question is whether the intrinsic factor and MMA tests would show anything if I stop b12 for a few days? I do not want to risk stopping for longer than that.
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Numbsew
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IFA isn't a particularly good test - a positive is good confirmation of PA unless done too close to supplementation - how long you need to stop depends on the exact test and varies from 2-10 days. However, its not very sensitive so gives false negatives 40-60% of time (exactly how insensitive depends on the exact test) - which meas that a negative is a long way from ruling out PA.
MMA may or may not be useful - unlikely you will be B12 deficient at the cell level at this point if your symptoms are improving so probably won't be useful.
Diagnosing a B12 deficiency in pregnancy is quite difficult as serum B12 levels drop significantly due to your body prioritising the foetus - so if you were diagnosed that suggests that your levels must have been really low.
Your body tends to regulate B12 levels quite closely at the point in the normal range which is right for you - its a huge range which just shows how much people vary in the level that is right for you. The fact that there is a very significant drop in levels - from 700 to 319 - would point to a B12 absorption problem, and the treatment for an absorption problem is injections.
With B12 deficiency the symptoms really are the best way of monitoring what is going on and there aren't really any reliable tests. Unfortunately asking your GP to refer to a neurologist or a haematologist may not help - or asking them to consult for an opinion - as many do not have a good grasp of how B12 works anyway.
I think your best option is probably to join and contact the PAS and ask them for some support
There is also a page on the website that you could suggest your GP look at but I'm not sure that it will really get over the issue of continuing with injections every other day until symptoms stop improving - which is what you are currently looking for
Another option would be to source your own B12 and start self injecting ... some people do find that telling GPs this is what they plan to do gets the GP to think again - but others find that it just riles the GP and destroys the relationship that is really needed between patient and doctor.
Thank you for your reply. I think my b12 in pregnancy was 112 but that was 23 years ago. I had low haemaglobin levels which wouldn’t come up despite iron injections. My grandmother had PA and suggested it might be the problem. (She had lost a baby at 26 weeks due to low iron and had almost died herself.) My GP initially refused to test for b12 ( he said that I was too young to be deficient at aged 26) but the midwife persuaded him.
I felt immediately better with one b12 injection. Prior to that I had been utterly exhausted and hardly able to walk or stay awake to look after my 2 year old daughter. I can’t remember if I had a loading dose but I know that my levels came up after I had finished breast feeding so the injections were stopped without a proper diagnosis ever being made. I have been symptomatic ever since. In my 20’s I was told I was just a tired mum, in my 30’s I had been put on antidepressants and told it was anxiety, in my 40’s told I just needed to lose weight, then, when I had lost weight, that symptoms were a result of dieting, then that I had IBS, now menopause but the symptoms have been the same throughout. Each time I have asked to have my b12 checked and each time I have been told it was normal. I now have a different GP and additional neuro symptoms. I am worried that the injections will be stopped again. He has already mentioned the “placebo effect.”
Personally get very very annoyed with the misuse of "placebo effect" as a way of dismissing people who respond well to B12 ... though more because the definition of placebo effect is that it involves something inert that could not possibly cause the reactions that are observed - which isn't the case with B12. Reality is that the placebo effect is an important effect and using it to dismiss really doesn't do the effect justice.
It would only be the placebo effect if he was substituting the B12 for something inert and you continued to respond (which would probably get him in to trouble with medical ethics committees).
The effects of a B12 absorption can take decades to materialise - I can trace symptoms back to pre-teens but wasn't diagnosed until my early 50s!
Its easy to get caught up in what ifs and I understand your concerns that the injections may be withdrawn but at the moment it's a what if.
If your GP does stop the injections then you do have the option to source your own and treat yourself.
It isn't an expensive medication and to be honest, given that it is so cheap the benefits you are experiencing would seem to me to make it well worth continuing with the 'placebo'.
you would need to contact the lab finding performing the test to ask them how long you need to be off B12 - no way of knowing which labs are preforming which tests.
To be honest your GP probably isn't aware of this limitation so if you are supplementing and go ahead with the test you could well get a positive that was a false positive but your GP wouldn't realise that. However, as my dad would say - 'two wrongs don't make a right.' - so not really an action I'd condone.
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B12 deficiency likely down to Ferritin 
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Average diagnosis time
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