B12 deficiency with High Serum B12? - Pernicious Anaemi...

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B12 deficiency with High Serum B12?

theverytiredperson profile image

I have B12 deficiency (non-diet related) probably PA although I I tested negative for the antibodies. I my serum B12 levels were low/ normal and I had scary neurological symptoms with it but no anemia, and it took a referral to a neurologist to get diagnosed. Since I have been having injections twice weekly I have seen so many symptoms resolve, some of which I had no idea were B12 related in the first place.

However, my mum who is in her 70s is currently very unwell. She has a wide range of symptoms, many of which could be explained by B12 deficiency. Her MCV is high at 109.1 meaning she has macrocytosis, although she does also have other abnormal blood markers (not indicative of B12 D) which have left her GP stumped. Her Serum B12 is 762 and folate is 9.8, so her GP is unwilling to consider the possibility of B12 deficiency. She has never taken any supplements which could effect her result.

Her results were referred to haematologist who wasn't concerned and said he didn't need to see her. I have been trying to get her a neurology appointment but so far without success.

I understand that Serum B12 762 would not normally suggest a deficiency. But is it possible to have a severe deficiency whilst also having a high/ normal Serum B12 result? My mum seems to be getting worse every day, with arm and leg weakness, hair loss, extreme fatigue, urgency for toilet trips etc and I would like a medical professional who understands B12D to at least rule it out, so I can be certain its not getting missed, before she ends up on another waiting list for months to see a rheumatologist.

Can anyone shed any light on the question of whether B12 deficiency is possible with a high/ normal Serum B12 result?

14 Replies

It is possible to have a high serum b12 reading and have P.A. ( before any supplementation of course . Once injections begin , the reading should be high and needs no further testing )

Vitamin B12 supplementation is so benign , and cannot be overdosed . Your mother would not be harmed in any way if she had B12 injections , even if it turned out that she didn’t have P.A. There is terrible ignorance in the medical profession about P.A. , as many members of this forum know to their cost . Also there is a strong genetic link ., indicated by you having P.A. About 50% of P.A. patients test negative for the Intrinsic Factor Antibodies test ( your GP should know this .)

If your GP. will not give her a trial of injections , do take her to a private GP . OR , some beauty clinics also will give B12 injections .

High Homocysteine levels can also be indicative of P.A. , but also of other conditions . Has that been tested ?

Part of the problem is that she is easy swayed by what the NHS doctors say. She starts off the consultation convinced its B12D and by then end of it is going along with what the doctor says. I have recently written to her GP on her behalf, explaining her symptoms and the family history and asking them to consider B12D. Whilst it did prompt them to take a bit more interest in her deteriorating state, they have talked her out of the B12D possibility. I've ended up questioning my own thoughts - who am I to think I know better than 2 GPs and a specialist?

I wonder how common it is to have nigh/ normal serum B12 results and also B12D (without ever having has any supplements or injections)?

Google “Functional B12 Deficiency” and read all about it .it stated that 7-30 % of the elderly have this , and can lead to neurological damage if not treated .

I imagine but your Gp being stumped nothing on her bloods has shown concern for her liver diabetes ect. or anything else going on. Its usually q matter of elimination if the medics are confused.

There I'd a thing called functional b12 deficiency. I think mma homocysteine levels are tested

I hope she finds out soon what is happening. T c

I would like to know why an Haematologist does not know about Functional B12 deficiency .

Gambit62 profile image

Functional B12 deficiency gets used in different ways but my understanding is that it generally applies to situations where serum B12 levels are high and above range. Its mechanism is something going wrong with the mechanism that allows B12 to pass from blood to cells meaning that there are high levels of B12 in blood but not enough is getting through to cells meaning processes there that need B12 are not running properly. Homocysteine and MMA are used as markers for this as they are products from 2 of the processes that need B12 but will build up if there isn't enough B12 available to recycle them. Both high homocysteine and MMA can be caused by other things so the tests need to be done in a context that rules these out (check for folate deficiency in the case of homocysteine and for kidney problems in the case of MMA.

Although the most common causes of macrocytosis are B12 and folate deficiency these aren't the only things that can cause red blood cells to be larger than normal. Identifying the cause may mean looking at other markers and you mention that there are other markers in the results that indicate problems


see section on details on CBC results.

If the other markers point to liver disease this could be the reason for higher B12 levels as liver disease can cause the liver to dump its stores of B12, but it doesn't look as if the levels are actually outside the normal range so it may just be that she is naturally at the high end of the B12 range and the fact that the symptoms are symptoms of B12 could be a red herring as the symptoms of B12 are also symptoms of a number of other conditions.

Sorry that there isn't a clear response to your answers. Suggest you speak further with GP and find out if they have consulted or are referring to specialists.

Thanks Gambit, I have certainly found the information available online about functional deficiency to be a little confusing, and there does not seem to be much of it. Since I posted this morning my mum has spoken to her GP again and is being told she may also have an enlarged heart. I believe this can also be caused by many different things (including anemia and nutritional deficiencies). At least they are now planning to do some more investigations.

Cherylclaire profile image
CherylclaireForum Support in reply to theverytiredperson

I was given a diagnosis of functional B12 deficiency (after injections for B12 deficiency started). The diagnosis was made by my GP and confirmed by the laboratory after MMA was found to be still raised about 9 months after B12 injections started.

Homocysteine level was "normal".

Haematologists told me that B12 was toxic, carcinogenic and highly addictive. Obviously no proof offered although I asked for it three times, and no similar stories for GP in feedback report. With no alternative reason found for continually raised MMA levels, it was decided that this was "my normal" for MMA.

Wrong. Last year, MMA was tested again and is now comfortably within range.

Frequent B12 injections being the only treatment given during this time (by myself mainly), I can only assume that my GP's diagnosis was correct.

Wow, I can't believe how ignorant some consultants seem to be about B12. It must have been worrying and frustrating being told that your treatment was toxic and carcinogenic. Its a good thing that you continued with your injections and are now feeling better.

So the reason for the functional deficiency diagnosis was that MMA was still raised in spite of injections suggesting that your system was not processing the B12 in the expected way? How regularly do you need to inject now in order to feel well?

I have been on twice weekly injections for the last 6 months, and sometimes I need to go to alternate days, in order to keep on top of my symptoms. My serum B12 levels are now off the chart. I am still unsure if this suggests a functional deficiency or if it just means that I need a lot at the moment in order to repair prior damage, because of having been undiagnosed for so long. And maybe I will be able to space them out more at some point in the future.

Cherylclaire profile image
CherylclaireForum Support in reply to theverytiredperson

When you have been waiting for months to see a consultant, have done your research, have kept a daily symptoms chart - despite exhaustion, confusion, cognitive problems and memory loss - it is highly insulting and time wasting to have to listen to statements you know to be untrue. Patients need to be able to trust consultants.

The reason for the functional B12 deficiency ? Possibly that my body felt overwhelmed with a sudden flood of B12 after B12 deficiency, and couldn't process it usefully ? I'm not sure. I got no change from the loading injections and a lot worse after having to wait 3 months, but I'm certainly not alone in that.

MMA level is supposed to be high when deficient but rights itself in a matter of days once B12 replete (which is the point of the loading dose). So if it remains high, there may be a problem. It can be renal or bacterial (small intestine bacterial overgrowth: SIBO) which can both be tested for - blood test, breath test respectively - and eliminated. Otherwise it can be a functional problem at cell or tissue level.

I was self injecting every other day for over 2 years, which I have reduced about 9 months ago to every three days. I feel okay, most of the time, but not as I was, and know that if I overdo it, I will have a few days of not-so-good.

Still have daily diarrhoea, burning tongue, stiff feet and back, memory problems and am slower- but most other symptoms have reduced in severity and frequency, are manageable or rare - not gone forever, so able to return if I try to reduce injections further in a fit of confidence/ optimism or if I overdo it (still difficult to judge at the time). For me, this is not a miracle cure, it's keeping symptoms at a distance where possible so I can have a life.

I expect my B12 serum level to be over measurable amount (over 2000 ng/L) and so I don't expect it to be measured now. My GP stopped checking that in 2016.

I have PA which went un-diagnosed for many years because serum B12 was always within the mid range of normal. It took an open minded practitioner (new one for me) who was willing to provide a full PA panel (MMA/HCY, antibodies, etc.) to find that I actually suffer from PA/B12 deficiency. She was concerned because I had ordered a neuro antibody panel from an online doctor and ended up testing positive for antibodies to myelin basic protein. (My local neurologist simply told me that he had no idea why I had come back positive for these antibodies and to come back if neuro symptoms got worse. He did run an MRI to rule out MS but said there was nothing else he could do.) It pays to be your own advocate and an advocate for those that you love.

Cakebake profile image
Cakebake in reply to EllieMayNot

Can I ask which company you used to carry out the test for you please?

Everyone needs different levels. If injections resolve your issues thats the indicator. I would say the high MCV indicates deficiency as large RBC.

Agreed with Wedgewood. Good advice. Spot on advice!

See Tracy Wittys website


Dr Joseph Chandy


Hello. I am dealing with similar symptoms as your mother, and I typically have very high B12--- above 2000--- without supplementation.

I recently read that there are genes which might be associated with high serum B12--- genes having to do with B12 transport. One protein is called Holo-Transcobalamin. This is a protein in the blood that transports B12 into cells. Only about 25% of B12 is attached to HoloTC, though. The other 75% in the blood is not able to transfer into cells but is still there.

So, in theory, it is possible to have a high total B12 level but LOW HoloTC. In this case, the usual B12 blood test would show you have normal or high serum B12--- but yet you could still show signs of cellular deficiency because your B12 transport protein is faulty!

This is all very recent research, and I don't know if there is a test to measure HoloTC.

How is your mom doing now?

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