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Pernicious Anaemia Society
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B12 levels with injections


I have been having b12 injections through my GP every 8 weeks for around 2yrs, after a diagnosis of low b12 levels (around 160). Luckily I am able to absorb b12 via tablets, so as well as my injections I supplement myself with a minimum of 1000mcg most days. If I don't supplement myself then within a week or two of my injection all my symptoms start to come back. I was never given any loading doses by my GP and recently they have been questioning my request to have an injection every 8 weeks, when the guidelines say that 12 weeks should be sufficient.

As a result, they asked me to have a blood test 6 weeks after my last injection. My understanding was that this was fairly pointless as once you are on injections your levels should be in the 1000s and the b12 should stay in your system for a couple of months. I didn't take any extra supplements for 5 weeks after my injection but by this time was feeling horrendous, so for two days running I took 2000mcg to try and top me up until after the blood test when I could start taking my supplements again.

I've just had the results of my test and my b12 level was 511 - am I correct in thinking that this is low for someone on injections who also took supplements the week before the test?

As I can absorb b12 through my digestive system, I know that I do not have pernicious anaemia and believed that my problem was always with the storage of b12 instead. Does the blood test result support this theory?

Luckily for the moment they have not said anything about changing the frequency of my injections but I am waiting with baited breath for the call from my GP as the nurse who gave me the results said they were 'perfectly normal'.

Thanks in advance for any guidance you can give me - I have done so much research on PA but I am not too sure what applies to me and what doesn't seeing as I am able to absorb it!


4 Replies

Hi lizzie4687 when you say you know you do not have Pernicious Anaemia have you ever been tested for Intrinsic Factor Antibodies?

The amount of B12 swirling around in your bloodstream may just be from your injections and as to your not having an "absorption problem" your having taken for two days running 2000mcg just before the test I would have thought your level would have been higher than 511.

Also do you know what your Folate level is and what sort of diet do you have? Can you eat meat, fish, seafood, eggs, poultry and dairy produce?

I'm not a medically trained person but there are others on here who will be able to give you good advice.



Thanks for your response. When I went through the diagnosis procedure I had tests for IF antibodies which came up normal, which is why I thought I did not have PA officially. Saying that, I have a family history of low b12 problems as my grandmother used to have b12 injections frequently, given by my grandfather who was luckily a GP, so I always assumed it was a genetic issue.

My folate level and iron levels are borderline, so as well as supplementing b12 I also take additional supplements for these and a multivitamin. I did not take any of these supplements during my 6 week wait for the blood test, so I would assume the levels had all gone down.

My diet is generally ok, although I don't eat eggs I do have at least one portion of meat a day, as well as a few of dairy.



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Others on here have said "Sadly the IFA test is unreliable in that it gives false negatives in people with PA half the time. So a negative result doesn't mean that you don't have PA. However, a positive result is a sure-fire, 95% certain indicator of PA."

You could always ask for an MMA test. Methylmalonic acid is a chemical used up in one of the cellular reactions mediated by B12. If there's not enough B12 in the cell then MMA levels will rise. If they're not high then it means your cellular levels of B12 are OK. High levels of plasma MMA (>0.75umol/L0 almost invariably indicate cobamalin deficiency.

So a blood test for MMA and/or hCys can tell if the B12 is doing what it's supposed to be doing. If the levels of the two chemicals are normal then B12 is working properly. If the levels are raised then one explanation is that B12 isn't working properly (there are other possibilities - MMA can increase because of kidney disease, hCys can increase if folate is low).

But the key is that if either MMA or hCys is low then you know that B12 is definitely getting into the cell and not just swirling around your body.


That is interesting to know thanks - I just assumed that as I started to feel better taking tablets I was able to absorb it.

I may investigate the MMA test although it would have to be privately as I don't think my GP would be keen to start doing any more tests.

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