Thyroid UK
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hypothyroid with high B12

when i was diagnosed the dr said my b12 could only be so high as a result of hypothyroidism. could anyone explain why this is?

now that i'm treated my b12 is still on the top end of the range but even so the MCHC on the full blood count test is high which is an indication of low B12. pls could someone enlighten me on all this. thanks

5 Replies

;A deficiency in folic acid could lead to this. Also, liver disease, hereditary spherocytes and vitamin B12 deficiency are sometimes responsible for this type of result. Burn victims also show elevated mean corpuscular hemoglobin concentration.'

'How to improve your MCHC levels

Before trying to fix your hemoglobin levels you should get testing to find out what reason(s) is causing your condition.

If the cause is a systematic condition like bone marrow defects, cancer, kidney problems then you’ll need to get specialized treatment.

If it’s being caused by certain types of drugs, then you might want to look for alternative medications.

If it’s due to nutritional deficiencies then you should eat more mineral rich food and/or create a supplement regiment. The most common nutritional deficiencies related to mean corpuscular hemoglobin concentration levels are iron, folate, vitamin C and Vitamin B12.'

Any of this ring any bells?


Your doc is not correct. It may mean nothing but high b12 may be associated w various disorders and diseases of the liver, kidney and blood. Yours may be none of those things but unless your gp has more info you can't just discount the more serious issues. I believe this is a German site but it may automatically translate for you as it did for me:

At the very least gp should be telling you why they've reached the conclusion that it is your thyroid. It's possible they've already looked into and rejected the more serious causes on the basis of other tests but it would be nice to know if that's the case.


have you supplemented B12 at all?

If you have signs of macrocytosis with high B12 that isn't caused by supplementation it can be an indicator of liver and kidney problems.

The condition you describe sounds like a functional B12 deficiency - B12 metabolism involves absorbing it from your food, transferring it from blood to cells and cells actually using it. Things can go wrong at all three points - though serum B12 only measures what happens in the first. High levels in blood can result in a reaction that prevents the B12 getting from your blood to cells - an auto-immune response - this will result in all the symptoms of a B12 deficiency (because there is none available to your cells) but your serum results will still be high. Markers that can help to clarify are MMA and homocysteine - which will be raised if there isn't enough B12 at the cell level - but they can be raised by other things.

suggest you do a search on 'functional deficiency' on the PASoc forum

I've not come across anything indicating a link between hypothyroidism and high B12 serum.

1 like

I also have always had mildly raised B12. Which I always found surprising. Folate was often high too. I have Hashimotos, gluten issues & low vitamin D.

When I started supplementing vitamin D, about month after I was getting peripheral neuropathy - burning feet especially.

After reading this Link

I added B complex (& B12 for about 6 weeks). I still take B complex (which contains some B12).

I did an active B12 test - results were with in range

Now use vitamin D lamp rather than supplements - works better for me.


A gut infection or bacterial overgrowth can cause this, plus other issues these wonderful ladies have mentioned already. Imbalance of bacteria can cause over absorption in the ileum. My dog had a life-threatening form of auto-immune disease which caused anaemia & lead to bone marrow failure, so I have spent 4 years studying the disease & haematology - he has 3 monthly blood tests - he had a Giardia infection which caused his B12 level to go over 2,000 which was a huge shock but not dangerous!!! This can also happen to us humans. Have you had any stomach issues? Just another idea for you to look at. Better high than low.


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