hi guys,
I had a positive intrinsic factor blood test back in April and this was before any b-12 injections. Since then, the doctors have wanted to do two other intrinsic factor blood tests and both came back negative and the doctors are confused
why is this?
Thanks,
Ella (:
They shouldn't be confused. False negative IFAB results are common for people with PA.
Doctors should know that Pernicious Anaemia patients can get negative Intrinsic Factor Antibodies tests .
As you have received a positive test , it is proof that you have Pernicious Anaemia. Tell the doctors to look up the facts about the IFAB tests . It is so annoying and dangerous for patients that they are not knowledgeable about Pernicious Anaemia.
My G.P also repeated the IFAB test after a positive result. Second one was more positive than the first, so they lucked out there.
Not sure why your Docs are confused with yours coming back different, as it is a notoriously innacurate test - only about 60% accurate, I think.
The senior doc has now put a note on my records saying do not review, to stop them ordering expensive and pointless tests.
Antibody levels [titres] rise and fall, like the tide coming in and out. Method sensitivities cary too.
Good luck.
They need to read the manual for the sensitivity and specificity of the test. Doctors these days. Honestly. *sigh*
That test when it is positive indicates you have a problem. Once you get a positive test result, there is no point in retesting. The test has a very high rate of false negatives.
If it’s a notoriously inaccurate test isn’t it possible it could give false positives too?
If you were in a room with no windows - just a door.
Every so often you open the door. Could be hours, days, weeks between door openings.
If it is dark, you find out nothing. But it just takes one time that it is light to see that there is a sun that can shine!
Here is a way to think about it mathematically. Supposed I have a coin hidden in my hands and it either has heads on both sides or heads on one side and tails on the other. I flip it and you see the result. If it gives you heads, you do not know anything from that experiment. If it gives you tails, you know that the coin has tails on one side of it. I think that the antibody test has close to a 50% false negative rate which is analogous to the coin coming up heads.
If it gives you heads, you do not know anything from that experiment
I do, I know the coin has a head on at least one side
I’m so sorry but I’m not getting it. Please feel free to ignore me though
I understand that when antibodies would normally be present, for whatever reason, on that particular day, other factors are at play that have rendered the antibodies absent or undetectable. Or have I got that wrong? What I don’t understand is why equally it can’t give a positive that’s wrong, a false positive. I.e., that on that particular day, it mistakenly detected antibodies present when normally they’d be absent
You may have lost the will to live by now but if you feel you have a way to make me understand, please save it till tomorrow 😂
I do appreciate your effort
That particular test has a very high false negative rate (around 50%) but I think it is very accurate when you get a positive result (95% chance the positive is correct).
Ok, thank you
From a recent link someone posted: Anti-intrinsic factor antibody (IFA) testing. Although IFA is extremely specific for pernicious anaemia (positive predictive value 95%), it has a low sensitivity of 40–60%, meaning that only about half of people with pernicious anaemia will have anti-intrinsic factor antibody (i.e. its absence does not rule out a diagnosis of pernicious anaemia). For this reason, the routine reflex testing of IFA when vitamin B12 levels are low is expensive with a low detection rate.
Intrinsic Factor test Negative :-(
Positive intrinsic factor 
Negative Intrinsic Factor & Parietal Cells
