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Pernicious Anaemia Society
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GP didn't order intrinsic factor test!

Hello, I went to my GP practice and got print-outs of all my blood test results, but discovered I never even had the IF test! Instead she did the gastric parietal cell antibody test (negative) as well as a number of others (all negative):

Anti Mitochondrial Antibody

Anti Smooth Muscle Antibody

Liver Kidney Microsomal Ab

Anti-liver Cystosolic ag. type 1

I've had loading shots and currently taking a sublingual daily so no prospect of doing the IF test right now anyway. I'm a bit flummoxed although I can see why the GPA test could be preferable. I just wonder if I will ever know if it's PA.

My other results:

Serum folate 6.8 ug/L (2.1-14.0)

B12 154ng/L (180-900)

MCV 102.2 (81-100)

Everything else well within normal range.

Interestingly, also got blood tests from May 2016 (so 12 months previously) and the MCV was 97.8. Makes me think the macrocytosis has been brewing all that time but nobody thought to keep an eye on it, or test B12/folate. Very annoying!!

I'd welcome any comments about the IF/GPA tests or the MCV count.

Thanks for reading! 😀

11 Replies

Hi Curlygal according the N.I.C.E guidelines on the treatment for B12/Folate deficiency it says:

Assessing B12 deficiency

How should I investigate a person with vitamin B12 deficiency anaemia in primary care?

Determine whether there is an underlying cause for the serum vitamin B12 deficiency (for example pernicious anaemia), by checking for serum anti-intrinsic factor antibodies.

Note that testing for anti-intrinsic factor antibodies is recommended in people with strong clinical features of B12 deficiency, such as megaloblastic anaemia or subacute combined degeneration of the cord, despite a normal vitamin B12 level. For more information, see the section on Interpreting results of investigations.

Checking for gastric anti-parietal cell antibodies is no longer recommended to diagnose pernicious anaemia.

Determine whether the person has experienced complications of anaemia, or of vitamin B12 deficiency.


Click on the link, then on "Scenario: Management" and scroll down.

Are you supplementing with folic acid as your level looks to be bumping along at the bottom?

I'm not a medically trained person but there are others on here who will be able to give you good advice.

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The anti-GPC test is no longer recommended because it gives too many false positives. But that's not the case here as you tested negative. If you follow the link given by clivealive above you'll come across this...

If anti-parietal cell antibody is not present it is unlikely that the person has pernicious anaemia

So it's likely that your B12 deficiency is down to something else.


Strangely , I have twice tested positive for IFA , but negative for anti-parietal cell antibody . I do have P.A. So that is not in line with the above statement in italics .

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I presume by the italic statement you are refering to

if anti-parietal cell antibody is not present it is unlikely that the person has pernicious anaemia

unlikely is not the same as impossible.

a negative on gastric parietal cell antibodies is much less likely to be a false negative than a negative on the IFA test so is quite a good guide.


Yes! I was covered in B12 patches and was taking sub-lingual methylcobalamin lozenges , and tested positive in spite of this . It all happened before I was aware of P.A. and the implications of supplementing with B12 before testing .


I'm confused aren't GPC antibodies and IF antiobodies tests for two different causes of PA? So even if you test negative for GPC you could still have PA and that's possible even in the presence of normal B12 levels?

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Hi thanks for all the replies! I had the parietal cell antibody test just before starting loading doses ie.before any supplementation, wasn't taking the sublingual then.

I was under the impression also that the two tests were two slightly different reasons for PA, but also read about 80% of PA patients are positive in the GPC test? Not sure.


Or rather, two slightly different manifestations of PA, if that makes sense.


I could ask my immunologist if she will test for IF, but don't see her until February. She's quite interested in autoimmune things and is forever checking my thyroid.


The two tests are for two different problems.

The IFA test is looking for an autoimmune response that specifically targets intrinsic factor (which is why, when it comes back positive, it's highly specific proof that the person has PA).

The parietal cell antibody test is looking for an autoimmune response to the parietal cells which happen to be the cells that produce intrinsic factor. A positive result for that test usually indicates some gastric atrophy is at work.

Both of these problems have the same result in that the patient will not be able to absorb B12 normally due to a loss of intrinsic factor. Gastric atrophy can also lead to some other problems with nutrient absorption as well as higher risk of stomach cancer.

My personal opinion is that it is goofy to 1. only do one of the two tests, since they are testing different problems and 2. assume that if the one test that is done is negative then the other test would automatically be negative also.

The doctor who found my deficiency was not especially knowledgeable on the subject and she mistakenly believed that she only needed to do the GPC antibody test. In my case that test came back positive and I was given a diagnosis. However, a year later when I had both tests run, they both came back negative, and I went into a limbo of no clear diagnosis. The real problem with antibody testing are cases like mine, where the results don't seem to make sense (once you start producing antibodies, you usually don't stop). The schilling test, which is no longer available, was more useful for determining actual absorption of B12. All of the tests that are available now are inferior because they cannot perform that basic measurement. The active B12 test is considered an advancement, but that advancement is not being compared to the accuracy of the schilling test. It's merely an advancement over the imprecise antibody testing that is currently standard. (/end of personal rant over testing)


I found this on the PAS site:

"The deficiency of intrinsic factor in Pernicious Anaemia can be caused by two mechanisms, either by the progressive destruction and eventual loss of parietal cells, leading to a diminished production of intrinsic factor, or by the presence of blocking antibodies that prevent the bonding of the intrinsic factor to vitamin B12."

So it would definitely make sense to perform BOTH tests, if I am reading this correctly.


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