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Pernicious Anaemia Society
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The good news and the not so good

Luckily my B12 deficiency is getting better, I’m still cheerful, can walk fairly steadily, balance getting there, leg numbness almost gone. As symptoms are still improving I am continuing weekly injections and supplementation in between. Thank goodness I ignored my NHS GP’s ideas of treatment (B12-103 <180-1000 with Neuro. symptoms = 5 loading injections, retest in 12 weeks, (now normal!) retest in 6 mths. and a walking stick for the Neuros.) Yes I did give them a copy of the BCSH Guuidelines.

The next bit is somewhat off topic but I as this forum is my support here goes.

I had an MRI which showed a large Frontal Sinus Mucocele which has to be drained by an operation. in ten days’ time. It was found by the Eye Dept. at the hospital, when I got double vision after a cataract op. I have to have a general anaesthetic. I’m not too bothered about the op. (I had researched it before seeing the consultant so understood what she was talking about) but one worry is that the nitrous oxide for anaesthetic will wipe out my B12. I will tell them and hope they know about the effect it has on B12.

Thank you to the PAS member who told me about an excellent private GP who gives me my injections. Thank you, members of this forum, for all the support, information, references etc. from which I have learnt what was needed. I have learnt a lot since January when I joined PAS. I don’t think I would have survived this op. without your help and the B12 injections.

I will post again if/when, being ancient, I get through this, !!! and will expect applause from everyone (and a corny joke from the king of puns.)

PS - Does nitrous oxide wipe B12 out of the blood (a good time for a retest?) or just inactivate it, so is still in one’s blood messing up tests?

6 Replies

Links about nitrous oxide


There is a highlighted box with advice for healthcare professionals which makes it clear that specialist advice should be sought in cases where people have b12 deficiency.

Could you speak to the PAS? Perhaps they can point you to other useful info on nitrous oxide anaesthesia.

PAS tel no 01656 769 717


The book "Could It Be b12" mentions nitrous oxide.



Link to old nitrous oxide thread on HU


If i ever have to have anaesthesia I will ask face to face and hand a letter over (with a request that the letter is placed in my medical file) that I am not given nitrous oxide and if there is no viable alternative to Nitrous oxide I will ask to be given a B12 injection before and after. Not sure I would get anywhere though with these requests.


I'd ask first if nitrous oxide will be used at all. It's not that common (anymore). If yes, then get some extra B12 just after.


Nitrous oxide oxidises the B12 meaning that it can't be used any further - which I think is different from actually removing it from the blood. I'm not sure if the oxidised B12 still shows up as B12 in a serum test.

This article implies that the oxidisation actually converts it to an inactive form of cobalamin which would imply that it would still be measured in a serum cobalamin test


- under rarities at the top of p3

don't know if fbirder may be in a position to clarify/correct if I'm misunderstanding


Hi Beginner1. Good idea to get a letter put on your medical file...and always mention it every time you attend.

If I ever sign a crescent form I always write in 'not to be given nitrous oxide' at the top of the form, for good measure.

I recently went for an endoscopy and they were not aware of the nitrous oxide / B12 deficiency 'thing' so be prepared to educate, as you go along.

My understanding is that there are anaesthetic alternatives so if they had planned to use it, then there are other options.

And you are quite win your rights to simply refuse to have it (a much safer option, and one I always take).

Good luck.

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This paper - jneuro.com/neurology-neuros... - mentions several cases where people presented with symptoms consistent with a B12 deficieny after exposure to nitrous oxide, but with 'normal' serum levels of B12.

Their case had serum B12 of 367 pg/ml (211-911) but her serum MMA was 2501 nmol/L (0-378) indicating a severe functional B12 deficiency. That suggests to me that the assay used could not distinguish between the B12 in the normal and oxidised states - and that the oxidised state is non-functional.

They also suggest that normal exposure to nitrous oxide will only cause a problem when that exposure is large and chronic (mainly recreational use) or when other factors have already lowered B12 levels.


Thanks for the advice and references again. My B12 should be well up with the weekly injections, and perhaps I can avoid the nitrous oxide altogether. If not I will arrange for injections as soon after as possible,

Back to watch the Olympics.

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