Pernicious Anaemia Society
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B12 overload

Just been to the doctors for my latest B12 jab..When first diagnosed myself (doctors clueless), b12 level of 30. 18 months later, had a blood test done then injection 2 days later, Doc phoned and said my b12 levels were sky high, . Went today for my 3 monthly jab and asked the nures who told me it was 1180 at the last blood test and when i informed her i had an injecton after that it was decided to go for a blood test again rather than a B12 jab.

How can this be if i have Pernicious anaemia? surely my body must be absorbing b12 from somewhere...

Cant wait to see what my levels are now.

4 Replies

Hi alanduke,

Firstly it is not uncommon to find high serum B12 levels after treatment with B12 has started. Some people seem to hang onto B12 in their serum levels, others not. What is in the serum B12 does not mean its all actually available to the body, as it needs further converting to B12 types that the body takes up (in tissue level). Have a read of this:

And if your GP starts to think he needs to cut you back on B12 jabs have ready to show this:

British Society for Haematology

Guidelines for the diagnosis and treatment of Cobalamin and Folate disorders


 Patients suspected of having pernicious anaemia should be tested for intrinsic factor antibody. Patients found to be positive should have lifelong therapy with cobalamin (Grade 1A).

 Patients negative for intrinsic factor antibody, with no other causes of deficiency, may still have pernicious anaemia and should be treated as anti-intrinsic factor antibody negative pernicious anaemia. Lifelong therapy should be continued in the presence of an objective clinical response. (Grade 2A)

Its how you feel that is important, test results once on treatment for serum B12 are only 50% of the picture, symptoms are just as valid.

I hope this helps,

Kind regards,



thank you.. when the blood tests results come back... what should i ask for other than just the b12 level... doing a full blood count.. as well as thyroid as i was diagnosed with underactive thyroid at same time as b12....


Hi alanduke,

I'd recommend you get copies of your blood tests, then you can see what has or not been tested. Also if you get all your previous (and future, you have a right to see them) blood tests you can keep a file and see what changes over time. It would be good to have had serum Folate tested and ferritin (= iron storage) as these are needed in good supply with B12 (and other B vits) to make good blood cells. All B vitamins need each other to be metabolised, and its not uncommon to become say folate def after starting B12 treatment, and or iron def etc. You could look at your MCV (size of blood cells) to see if they go down in size with treatment, if still to high then you could also now be folate def, or your thyroid meds need adjusting etc. If MCV is to small then you may be iron def. As you have an underactive thyroid you may find you also have problems with taking up iron. B12 treatment can mean thyroid meds need adjusting, so lots to look out for.

Someone once said on a site that if you fill up your car with petrol that does not mean it will always run smoothly, some other problem may be causing the petrol not to get where it should, or other things are wrong with the car. I like that one, it explains so much about this weird you have had your B12 jabs so you are fine, or you have got to much petrol in your harm is known from to much B12, dreadful harm is known from to little B12 in a body.

Wishing you good luck,l

Kind regards,



"If you fill up your car with petrol that does not mean it will always run smoothly, some other problem may be causing the petrol not to get where it should, or other things are wrong with the car" - priceless! ;-)

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