Pernicious Anaemia Society
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Repeating IF test


I saw a new GP today, and he suggested a whole new set of bloods, with a possible referral to a haematologist and possible IV iron. So far, so good, apart from the delay for appointments, when I'm feeling so tired, breathless and spacey. However, he was the first GP to wonder why I'm B12 and iron anaemic. The others have all said that the 'why' is not important.

I'm not sure he's really knowledgeable about B12 because he suggested a repeat B12 (I did say this would be high). He also suggested a repeat IF test. Please can someone tell me if this is worth repeating? My first test last summer came back as negative, and that was before I started the injections.

12 Replies

Hi spacey1 I'm not a medically trained person but as I understand it the IF test is notoriously unreliable.

Have you had your Folate tested? Folic acid works closely with vitamin B12 in making red blood cells and helps iron function properly in the body.


I've been taking folic acid daily since Christmas, so I'd be surprised if that was low. I will make sure it's on the list for testing, though.

I know that as a test for PA, the IF test isn't great, but won't a repeat of it just give the same results as last time? I'm happy for them to test it - they can test what they like as long as I end up feeling better! - but I wondered whether it was worth testing again once injections had started.


I had to have the "Schilling" test twice 49 and 45 years ago (which pre-existed the current test) before I got a diagnosis of P.A. in 1972. This was generally held to be more reliable but the NHS had difficulty in sourcing the radioactive isotope used.

I don't understand why the current test is unreliable because as I see it you either have Intrinsic Factor or you don't. Hopefully someone on here will be able to explain.

On page 23 in the book “Could it be B12? – an epidemic of misdiagnoses” by Sally M. Pacholok R.N., B.S.N. & Jeffrey J. Stuart, D.O. there is a list showing:-

Who’s at greatest risk for B12 Deficiency?

Anyone at any age, can become B12 deficient. However, certain people are at an elevated risk. They include the following:

Vegetarians, vegans and people eating macrobiotic diets.

People aged sixty and over

People who’ve undergone any gastric and/or intestinal surgery, including bariatric surgery for weight loss purposes (Gastric bypass).

People who regularly use proton-pump- inhibitors. H2 blockers, antacids, Metformin, and related diabetes drugs, or other medications that can interfere with B12 absorption.

People who undergo surgeries or dental procedures involving nitrous oxide, or who use the drug recreationally.

People with a history of eating disorders (anorexia or bulimia).

People with a history of alcoholism.

People with a family history of pernicious anaemia.

People diagnosed with anaemia (including iron deficiency anaemia, sickle cell anaemia and thalassaemia).

People with Crohn’s disease, irritable bowel syndrome, gluten enteropathy (celiac disease), or any other disease that cause malabsorption of nutrients.

People with autoimmune disorders (especially thyroid disorders such as Hashimoto’s thyroiditis and Grave’s disease) Type 1 diabetes, vitiligo, lupus, Addison’s disease, ulcerative colitis, infertility, acquired agammaglobulinemia, or a family history of these disorders.

Women with a history of infertility or multiple miscarriages.

Do you "see" yourself in any of the above "people"?


I've been vegetarian for 30+ years, but I do eat dairy - and marmite! Apart from meat and fish, my diet is varied and it's healthy.

I've also had IBS for about 20 years, and I recently saw a gastro who explained that iron and B12 are absorbed in different places in the gut. As I was also VitD deficient, he thought it was possible I don't absorb nutrients very well.

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"I don't understand why the current test is unreliable because as I see it you either have Intrinsic Factor or you don't. Hopefully someone on here will be able to explain."

It is unreliable because the test doesn't look for the presence of the intrinsic factor protein itself. It looks for the body having an autoimmune response (generating antibodies) to that protein.

Now I don't know how scientifically sound this notion is, but I do remember someone suggesting once that, if you're body stops producing any intrinsic factor at all, the immune system response is likely to be zero - meaning there would be no antibodies produced because the offending protein doesn't exist. Either way, the test banks on the idea that you are constantly generating antibodies to IF if you have PA, but that turns out not to be true. The immune response appears to fluctuate.

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I think Martyn Hooper was tested 4 times before IF finally came back positive - so may be worth doing it again. Basically a negative doesn't rule out PA but a positive (unless the sample was taken shortly after a shot/high dose supplementation) would show that you do.

If last time gave a false negative then that doesn't mean this time would also give a false negative. There's a 50% chance that it will give the right answer - think of it as tossing a coin - 50/50 on whether it comes up heads or tails and the result of the second toss isn't dependent on the first toss. Sometimes the test will give the right result.



It's possible to have Antibody Negative Pernicious Anaemia (PA where IFA test result is negative). It's possible that your GP may not have heard of Antibody Negative PA.

Link below to flowchart from BSH Cobalamin and Folate Guidelines; mentions Antibody Negative Pernicious Anaemia.

BSH Cobalamin and Folate Guidelines

I am not medically trained, just someone who has spent years trying to find out was is wrong with me.

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Thanks, all, that's so interesting. I'd no idea that IF antibodies could fluctuate. As I self-inject, how long do I need to leave after a shot until I have the IF test? The surgery don't know I supplement and think I have one every eight weeks. I'm injecting once a week at the moment, although I think perhaps I felt better on twice


Link below mentions leaving between 48 hours and 2 weeks after a B12 injection.

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well I have just come off the phone for my DD results to be told that although she has a positive result for Intrinsic factor it doesn't necessary mean she has PA.... going round and round in bloody circles


The intrinsic factor test is very accurate for PA if it comes back positive. Something like 95% accurate. There are very few false positives.

False negatives are a different story.


thats what I thought. Just have to wait to see what happens at the haematologist appt


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