Pernicious Anaemia Society
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My Intrinsic Factor came back negative, with a range 0-25, does it have to be over 25 to be positive please?

Hi, My result was 4 AU for the IF test and just wondering if this needs to be over 25 to be positive please? I'm gathering the AU stands for what it's measured in? I presumed it would be a positive or negative result as I thought you either have them or don't? Does 4 mean they are present in a low amount?

Many thanks Jo

6 Replies

AU, as far as I understand, AU means 'Arbitrary Units'. Often test results are reported as 'Positive', Negative' or 'Indeterminate' without any numbers. I'll guess that they sometimes add the numbers just because doctors really, really like them.

Yes, 4 means your test is negative. Which tells you nothing as many people with PA get negative results. 

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Thanks, so guess given the range it would need to be more than 25 to be considered positive. I just assumed you either had the antibodies or don't, so don't really understand the number. 

It's a bit of a lottery that test, isn't  it! 

I requested the parietal cell antibody test, but doesn't look like that was done, I guess it's because it isnt considered to be as useful in diagnosing PA?



In any test there will be some background noise. Even a supposedly zero sample might give a small positive response. For most tests that are Yes/No/Maybe a 'Yes' is a big response.

Yes, the anti-IF test is a bit rubbish, but there doesn't seem to be much of an alternative.


Hi. I'm waiting for this result too. You can still have pernicious anemia even with a negative result as only about 50% of PA patients are positive. Look on the mother site and you'll see documents that confirm this.

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Yes, thanks still searching. My Drs first words were that I haven't got PA because negative IF and my Active B12 wasn't low enough- although it was 27, bottom of the range and the MMA was 430 more than top of the range! 

Have you got your result yet?


Not yet. He told me it takes two weeks, so 4 days to go. He didn't accept the private test results for b12.  Are you going to show him the evidence? NICE  no longer recommend the parietel cell test. Look at for evidence. 


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