Log in
Pernicious Anaemia Society
16,654 members11,533 posts

Low B12 with 'normal' MCV/MCH

I'm still trying to get to grips with the details of my issues, having finally see some possible light at the end of a long tunnel. I did search for a similar post, so apologies if I've missed one.

As I understand what I'm reading, PA is a macrocytic anemia, so would normally result in a high MCV on the blood count.

My neurologist requested a Full Blood Count along with other things, which is what showed up my low B12 (118 ng/L). However, the blood counts don't seem to match up with a 'usual' PA case?

The ones I think are relevant are:

MCV 85.1 fL (Range 80-100)

MCH 28.5 pg (Range 27-34)

MCHC 334.0 g/L (Range 315-345)

(Others available but I won't make the post too long by putting them all)

I am due to have the IF test on Monday, so hopefully that may clarify things (I'm aware of the low sensitivity of this test).

I think have read somewhere (can't find where and I've read so much in the last week my brain is muddled) that PA can occur in a small percentage of people without the usual raised MCV.

(EDIT - i think I found the reference - the British Journal of Haematology guideline

"The absence of a raised MCV cannot be used to exclude the need for cobalamin testing because neurological impairement occurs with a normal MCV in 25% of cases (Lindenbaum et al, 1988; Healton et al, 1991).


That doesn't seem to necessarily relate directly to PA though, just B12 deficiency..).

I've also read that an Iron deficiency can lower MCV, and thus iron deficiency and PA together can cancel each other out with regards to this result.

Unfortunately, the blood test doesn't seem to have tested iron (would show as ferrite on the test I believe?) - and I'm not clear if any other markers would suggest that?

I'm guessing that it will be worth getting my iron checked to rule that issue in/out (If it hasn't been tested in previous blood tests over the last couple of years)

Failing that, I guess my rather meandering question is whether a low B12 with a 'normal' MCV is more likely to mean iron deficiency + PA, or PA without classic large cells - or possibly an alternative non-PA cause for the B12 deficiency?

It's fairly clear that I may have do to much of the investigative work if I want to get to a final resolution, so any ideas on what I should be reading up on/investigating would be appreciated.


6 Replies

As you say, iron-deficiency anaemia causes small red cells and B12 deficiency anaemia causes small cells. So a combination the two can give a normal MCV. But it will also result in a high RDW (Red cell Distribution Width). Was that included in your tests?

But macrocytic anaemia is a symptom of PA, but not a necessary sign. It is one of the last symptoms to develop.



Thanks for the reply...

RDW was 12.3% (Range 8-16)

Not sure if that counts as high or not?

So it wouldn't be unusual to have neurological symptoms first, before macrocytic symptoms develop?

I guess that is why all the guidelines say to treat the symptoms even in the absence of confirmed test results?



stat: 25% of those with B12 deficiency present without macrocytic anaemia.

treatment on basis of symptoms relates to a) risk of permanent nerve damage if there are neurological symptoms b) fact that serum B12 is a problematic test and will miss 25% of people who are B12 deficient but also pick up 5% who aren't.

your mcv etc aren't low and RDW isn't high which suggest that there isn't any mix of iron and folate/B12 anaemia going on.

1 like

Thanks, that makes sense - Seems like an Iron test may not be so important then? - I will likely mention it in the letter I plan to write to my GP.

I'm having a brain MRI in a few weeks to rule out other issues - would it be expected for the sort of neurological symptoms that tend to happen with PA to show up on an MRI, or would the symptoms have to be really serious to expect anything to appear?


severe B12 deficiency can cause lesions in the brain and lead to dementia. Not really sure if the other effects of not having enough B12 on the nervous system (it mucks around with the efficiency with which you can reset neurotransmitters and can also lead to degradation to the myelin sheath that insulates nerve cells and is essential to efficient operation) would show up in an MRI. MRI would probably be more useful in ruling out other issues.

Try not to get too hung up on PA as a label as this is, strictly speaking a specific condition that would lead to absorption problems and a B12 deficiency. Tests are currently particularly inconclusive in ruling out PA as opposed to another absorption problem and the treatment for a B12 deficiency caused by an absorption problem is the same (with minor variations in relation to maintenance for those like h pylori infection that can be treated so you no longer have an absorption problem)

1 like

Thank you again - that makes sense.

My journey started with a shoulder xray then orthopaedic referral because I have two slightly degenerated discs in my neck that are narrowing the space for the nerve (but supposedly not pinching it based on a cervical MRI).

My osteopath's view was that this narrowing might be scraping the myelin of the nerve and causing my tingling fingers, but at the time B12 deficiency wasn't on my radar.

Seemingly nothing showed up on the cervical MRI in relation to the nerves in my neck, or at least not that was noticeable.

That became a possible cubital tunnel issue, ruled out by more nerve tests, then a referral to a neurologist, who finally thought to check vitamins.

I dread to think how much the various tests have cost (another MRI and EEG to come) compared to what might have been a simple test early on and simple, cheap treatment!

Still, progress is progress...

I appreciate your time replying and hope that I can give something back in time to what is clearly an important and useful forum!


1 like

You may also like...