Log in
Pernicious Anaemia Society
19,063 members13,067 posts

High active B12 but I have all the symptoms of B12 deficiency

Hi I have just got my results back from medichecks for active B12 which is 256 pmol/L which they say it's high. I'm not on any supplement and the reason I had the test done is because I am having all the symptoms of B12 deficiency. How can this be? I have brain fog, anxiety, I can't remember things and names, I can't retain information, I can't sleep, I have recurring sores in the corners of my lips, pins and needles in hands and arms and feel confused. Also titinnus in my ears and joint pain. Sometimes I have an electric shock type of pain down my leg. I had low ferritin (although within range) and took iron tablets for a while. I stopped these a few months ago as Dr suggested to stop them and see if the symptoms came back. Had brain fog before but never the tingling in hands and arms. In the past I also have shortness of breath and extreme tiredness and got these now. Can I be B12 deficient when active B12 is normal/high?

Had my thyroid removed due to Graves disease 4 years ago. I'm on thyroxine but latest TSH/T4 in range, if anything T4 towards the higher end but in range. So desperate to understand what's going on.

14 Replies

It is possible to have a functional B12 deficiency, where there’s lots in the blood but not much is getting into the cells. You can test for this by getting blood tests for Methylmalonic acid (MMA) and/or homocysteine (hCys). These are two chemicals used up in reactions mediated by B12. Too little B12 in the blood causes the levels of these chemicals to rise.

But the symptoms of B12 deficiency overlap with many other conditions. Outs possible that you have one, or more, of those.

1 like

Thank you so much fbirder. What I don't understand even from these forums is the difference in symptoms between B12 deficiency and folate deficiency. I'm sure my foggy brain is not helping right now


Hi Josie26

Please don’t worry about not understanding things on the forum. I don’t understand what active B12 is that was mentioned.

I had terrible brain fog.. could hardly communicate with anyone verbally.. palpitations on a night time, anxious all the the time and feelings in my tummy that I had done something wrong!!! Terrible electric shock feelings in my finger tips, occasionally I felt as if my head to the left side did an involuntary movement tinnitus on a night time.... bloods came back B12 deficiency, VitD3 and thyroid borderline... apparently I have learned from this forum that all three go hand in hand. Sorry about talking about myself!!! VitD 3 have you had yours tested.... my problems with brain fog and communication problems improved tremendously.

My problem now is my B12 is showing to be high at 2000 whatever ... even though I was told my bloods were normal range....!! Not sure what to do about it as can’t get a doctors appt!!

Please persevere this forum is very good and someone I am sure can give some reassurance to you.



Thank you so much Pambow. Yes I'll ask the GB to test for vitamin D and will ask if they're willing to test MMA and homocysteine as suggested by fbirder. I doubt it though as GPs seem to be concerned about saving money in the short run and when complications arise due to lack of investigation of symptoms it cost the NHS more. I just want to feel well. In my job I'm required to think and I cannot do that right now which rises the anxiety even more. Does anyone know though whether it's worth checking intrinsic factor antibodies if active b12 is at 256pmol/L?


Hi Josie,

Good to hear from you.... It’s actually Vit D3 .... hope you get sorted.

The symptoms of the deficiency are very similar to B12 deficiency.



Hi fbirder and anybody else. I have been reading some of the posts on functional b12 deficiency and there is a helpful YouTube video there about b12 not being absorbed at cellular level even though there's plenty of B12 in the blood. My recent active B12 test was high on 256 with no supplements. Does it mean that the intrinsic factor antibody test is of no use in my case because there is active B12 in the blood from the stomach?

Going to GP tomorrow so will ask for MMA and homocysteine but wondering whether to ask for Intrinsic factor antibodies at all. I need to pick my battle so to speak as the consensus on this forum is that GPs are so reticent in testing for anything.

Thank you


B12 is carried around in the blood attached to one of two proteins - haptocorrin (HC) and transcobalamin (TC). Nobody knows why the HC is there or why it carries B12 around, because it seems to be useless.

The B12 bound to TC is what we call ‘active’ B12 (or holotranscobalamin). This is the stuff that can enter the cell. A high serum B12 but low active B12 is a good sign of a functional deficiency.

But there may be other causes where active B12 is high but it still can’t get into the cell and do its job: the protein that transports it into the cell might not work properly; or the enzyme that cleaves B12 from TC; or the enzyme that removes the top ligand; or the transport mechanism that moves the cobal(II)amin around the cell; or something else I’ve not thought of. There is no evidence for any of those ideas, but there’s no evidence for any cause.

So do get MMA and hCys tested as they’re the best indicators of a functional deficiency.

As for the IF test...

Intrinsic Factor is yet another protein that carries B12 around (it’s too big to do it by itself). This one is responsible for getting B12 from the ileum (the last bit of the small intestine) into the blood. If you have antibodies to IF then you don’t absorb B12. So your active and serum levels would be low.

If you have high active B12 but aren’t taking supplements then it’s extrmel unlikely that you have a toy to IF.


Thank you fbirder, very knowledgeable. I'll ask for MMA and hCys to be tested only.

Maybe I just have iron deficiency anaemia and not B12 deficiency at all or I have folate deficiency? Are the symptoms between the 3 the same?

Pejka62, it's the active B12 test I was referring to but I think you're talking about serum B12.


The shortness of breath and fatigue could be caused by iron deficiency anaemia. But the pins and needles are unlikely to be caused by that. However, there are many possible causes.

I would ask to see a neurologist. There are various tests that they can carry out that can differentiate between various causes.

Folate deficiency is much less common that B12 deficiency. Because folate is a fairly small molecule it doesn’t have the problems getting absorbed that B12 has.


t is certainly not high at 256--should be 400 to 900--I was 211 and had nerve damage and muscle wasting--after 2 years of shots my leg muscle are about 70% back but some will never come back.


Hi Josie there doesn't seem to be any hard or fast rules with B12d I had Serum B12 well in range at 358 & high Active B12 at 128 too but I had been supplementing for 4/5 months prior but still had all the symptoms, it wasn't until I had the injections that things started to improve. You might find this link interesting as it basically says the tests mean nothing even HCy & MMA can be normal but you can still have B12 deficiency bmj.com/content/349/bmj.g52... .... Best Wishes x


Hi josie26

Just a question, have you ever had the air quality in your home tested? Some of the symptoms you have could be related to mold. These are: insomnia, sensitivity to static shocks, anxiety, depression, abdominal pain, diarrhea, brain fog, shortness of breath, tinnitus, numbness and tingling, headache, extreme fatigue, difficult word finding, difficulty with learning and assimilating new knowledge, loss of memory, extreme thirst, urinary frequency, vertigo (dizziness).

These overlap with the symptoms of a B12 deficiency as well as low ferritin, folate, vitamin D, thyroid problems. I would have your MMA and homocysteine levels checked as well as the aforementioned by the others on this forum.

I ask, because I lived in a moldy house, as well as having a B12 deficiency. It's very complicated because all of out body systems are so interconnected. What affects system affects another.

Take care, and I wish you the best.


Thank you all for your support. Going to the GP this afternoon and will definitely ask for MMA hcys iron folate and vitamin d3. I had low iron and ferritin in the past so it might be iron deficiency anaemia but I'd like to get to the bottom of B12 issue as well. Wish me luck. Difficult to reason with Dr when one has brain fog! T4 for thyroid came back high so I'm reducing my thyroxine and I know that high T4 causes anxiety, weight loss and trembling but I'm not aware of it causing all the other symptoms no have. Terrybraden thank you for your suggestion. No no mood or damp in my house so I can rule that out.


That’s good. My mold problem was very well conceiled. That’s why I ask. Anyway, hope that the B12 helps your brain fog. It sure helped mine.


You may also like...