Thyroid UK
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Active B12 results are back ... now even more confused

Hi all, I really appreciate your comments and feedback. I will post on the lupus site too as I have a number of AI conditions the symptoms of which I cannot tease apart without help.

Currently I am taking plaquenil for UCTD, I am coeliac and I take 100mcg of thyroxine for being hypothyroid. I have many new and debilitating symptoms such as random pin pricks - even in my eyes and behind my finger and toenails, lightening bolt pains through my feet and up my legs, blurred vision, double type vision (optician says tear film breaking up and now referred me to a consultant).

I also have much more extensive joint pain in my fingers and wrists, rashes on roof of mouth, ulcers and blisters on my hands. Now, after seeing the orthopaedic consultant I need another operation on my shoulder - I am in constant chronic pain, hardly sleep and I am trying to hang on in there as a school teacher; I have dropped down to 3 days but the pace and the pressure are overwhelming.

In the autumn my GP tested my serum vitamin B12 which was 284 (225 - 1100). My GP agreed to my trying a sublingual spray for a few months but it made no difference so I came off it 2 months ago prior to paying privately to have active B12 test, my results are below:

99 pmol/L (25.1 - 165.0) says within normal limits.

Can anyone explain how it was deemed that the first one was low while the second within range? I don't know whether the active one was affected by the sublingual, though I was off it 8 weeks before the private test.

Any Comments and insight appreciated.

5 Replies


Last year my serum B12 was 377 so I supplemented with a sublingual spray 2400iu daily for 4 months.

I stopped for 2 months to have the Active B12 test and it came back top of range. This was done through

St. Thomas' level 107 range 25 - 108 and St. Thomas say if its below 70 this is classed as a grey area and an MMA test is advised.

I had another one done last month so 4 months after stopping the supplement, this time with Blue Horizon and it

came back as level 69 range 25.1 - 165 They do not have a grey area.

So what I think is that even though they advice is to be off the supplement for at least a month before testing it proves in my case that after 2 months the supplement was still in my systems but after 4 months it is not.


The Active B12 blood test is different to the serum B12 test the GP takes.


Measures all circulating Vitamin B12...

...but not all B12 in the blood is available to be used by the body. The majority of vitamin B12 that is measured by the Total B12 test is that bound to haptocorrin, but B12 attached to haptocorrin cannot be used by the vast majority of the cells of the body. Only B12 bound to transcobalamin, Holotranscobalamin or Active-B12, is taken up from the blood into the cells of the body. This means that the Total B12 assay could give a misleading result and still be within the normal range, even though levels of Active-B12 are low. Imagine looking at a fuel gauge indicating that the tank was full. However if the tank was wrongly topped up with diesel, on top of the petrol that it really requires, the engine will come to shuddering halt.

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Think it may be time to have further testing with things allied to B12. Hopefully the above link will be useful....


Thanks all...I have been reading the info over a few months now... I am certainly not attributing all my symptoms to B12 deficiency.

I suppose what I want to know is, after finding out this active b12 result, am I nearing deficiency or not as the total test revealed? Still no nearer to understanding if I am or not or whether it is worth supplementing / having injections.


Hi bestbuddy - yes my serum B12 increased substantially just by taking soluble tablets for 4 months. I think the active B12 is far more relevant


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