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Pernicious Anaemia Society
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Blood tests after supplementing B12?

I have been supplementing with Jarrow 5000 mcg Methylcobalamin plus Thorne Research's B complex for nearly a year now and noticed a marked improvement in my symptoms, however I feel I am "not quite there yet".

If I were to go to my GP and ask for more blood test's (good luck with that i hear you say!) , which ones would still be relevant given that I have been supplementing?

The ones I've seen a reference to are:-

Active B12

Intrinsic factor



I realise the standard tests are pointless but a little confused as to which ones would still be useful?

I also recently discovered that my late father had been treated with regular B12 injections for the last few years of his life before he passed away , so would it perhaps be worth me being tested for the MTHFR gene as well?

10 Replies

If you look at the pinned posts you will see that all of the tests you have listed have a recommendation of 3-6 months without supplementation.

IFA is the only test suggested with a lower period without supplementation - about a week - but that is a test for a specific cause of B12 deficiency ... and as a test is prone to give false negatives 50% of the time.

MTHFR may or may not be a factor - it is one gene that can affect processing of B12 but if you are in the UK the NHS really hasn't got much of a clue when it comes to looking at genetics for treatment - US is slightly different - but even so it is only one possible cause of a B12 problem. There are other genes that are involved in processing of B12 as well, just that MTHFR is the one that seems to have caught the imagination most.


I see, perhaps I am being a bit naive, but I was hoping that there would be a test that would help persuade a GP to prescribe some B12 injections. My B12 level is 234 so I'm expecting them to refuse as I'm " In range". The frustrating thing is that I know I'm on the right lines, as if I stop my B12 supplements my symptoms come back with a vengeance, ergo I have a deficiency ! I suppose I will have to wait until I get peripheral neuropathy (i.e. nerve damage) before they will act?


Hi seamail57 I was in the same boat as you a year ago, I went to see a private Neuro and he treated based on symptoms and and test result of 233, I now have injections every 2 weeks which really helps, he then made a appointment nhs and I've had a few more blood tests and a MRI going back on the 24th Jan to get results, it's been 4 months now and I'm just starting to feel it's working but I could not go the standard 12 weeks, if you look at the guide lines, Drs at to treat according to symptoms even in a grey area in which we are, best wishes.


Hi Leo

Thanks for your reply - actually that's very encouraging, approximately where is this consultant based? (I live in Scotland) . Strangely enough when my symptoms first started to develop - forgetting names,, loss of balance, clumsy typing, poor handwriting etc. , GP referred me to a neurologist who said he didn't know what it was but that it wasn't a dementing episode so not to worry about it! Sounds like you found a better one than I did!



He is very good but a long way for you, he treats anyone below 350 I would certainly get your injections sorted before any damage accurrs.



Hi Julie

That's very interesting, especially the bit about treating anyone below 350 ! I see he is based not too far from Stanstead airport so just a one hour flight from Scotland maybe! Did you have to be referred by a GP to see him?


Morning, my husband rang and spoke to his secretary about how I was and how poorly I was feeling, so the apointment was made , but you can be referred, Stansted is about 1/2 hour away from Springfield. It was my Dr who said he like to treat patients below 350, I took all my blood tests and a list of symptoms, also took my B12 tabs with too, he looked at my history of under active thyroid and removal of gall bladder, which also does not help with B12 issues. Hope this helps you.


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Hi Julie

That's really helpful, thank you so much!



Is your supplement a melt under the tongue sort. I have just got one called superior source no shot Methylcobalamin 1000mcg plus B6 and folic acid, I have no idea if they are any good yet but this is the sort we can utilise I believe? Sublingual?



Yes, I use 1 x Jarrow 5000 mcg Methylcobalamin taken under the tongue daily and supplement with BetterYou oral B12 spray. I also use Thorne B complex as my folate levels were below mid range . I have to take both B12 sources daily otherwise I notice the return of my symptoms and just recently they don't seem to be working as well hence my question about further tests and injections.


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