Intrinsic Factor Test

[NJPoet]

If a person is on daily or EOD B12 injections, could that affect an intrinsic factor test? Meaning, could that result in a false positive?

[still_elsewhere]

My understanding is that once injections start, an IF test is likelier to result in a false positive? — but I’m a layperson (have only been in this community and learning since the fall).

On another note, I’m also in NJ and trying to write! (Published a few poems in journals years ago and am trying to rejoin that world, albeit with creative nonfiction this time.) Do you know of any friendly writer’s groups?

[NJPoet in reply to still_elsewhere]

What part of NJ? I’m near Princeton.

[still_elsewhere in reply to NJPoet]

I’m in the Jersey City area!

[Nackapan]

Yes I think if youve a high amount of b12 in your bloodstream this can happen.Mosf doctors if they do it insist on it before loading doses.

Some have more tgzn one test before getting v s positive one. Thdn for some reason doctors retest??

I've never had one. Didn't even know about it at the time

[Hidden]

Yes it can. It is recommended that you stop injections one or two weeks before testing for IFAB.

[jimmel196]

I had the same question when I was first diagnosed a year ago. I researched that very topic and got the following information. I depends on the assay (testing procedure) that is used by the lab performing the test. Most labs will tell you to be off of your b12 injections for at least 1 week prior to your test but they prefer 2 weeks off of b12. My physician uses LabCorp for their outside testing. I contacted the head of the immunoassay dept at my local LabCorp who told me that the assay they use is not affected by b12 levels so it would not matter with them. Apparently different labs use different testing assays. I hope this helps.

[NJPoet in reply to jimmel196]

Thank you so much. This helps tremendously. I used Labcorp as well. That was what I was told, but I wanted to ask around. I appreciate you taking the time to answer my question.

[fbirder in reply to jimmel196]

Yup.

Over the years there have been many assays for these antibodies. The original Radioimmunoassay (RIA) from the early 1980s required a gap of up to 3 weeks between an injection and testing. The later RIA in the late 1980s required a gap of two days (or maybe two weeks). About 13 years ago an Enzyme Linked ImmunoSorbent Assay (ELISA) was developed that suffers no interference from B12 in the blood.

One would hope that all labs were now using the ELISA assay.

[anon4035]

I don't know about if an injection changes the outcome IF, but in general the anti-IF antibody test is "relatively insensitive"

"To afford the distinction between pernicious anemia and other causes of low cobalamin levels, it is necessary to test for serum autoantibodies.5 The anti-IF antibody test is a relatively insensitive (50–70%) yet highly specific (>95%) investigation;5 in contrast, the anti-PC antibody test has a sensitivity of >90% but a specificity of only 50%.8 For this reason, the anti-IF antibody assay is the preferred test according to the BCSH, and assessment of anti-PC antibody titres is not recommended.2 Unfortunately, no test is currently available for FBCM; the Schilling test was used to exclude IF-mediated vitamin B12 malabsorption, but it is not currently clinically available.5"

This quote is from this article, which is a very helpful read, imo on b12 deficiency.

ncbi.nlm.nih.gov/pmc/articl...

The only method I personally (not a doctor!) believe you can take to rule out pernicious anemia is multiple anti-IF antibody tests and an endoscopy to actually check your stomach for h pylori, and take a sample to look at your intrinsic factor.

Something interesting is that " pernicious anemia now accounts for a minority of all [b12 deficiency] cases." I've been trying to learn more about food-bound cobalamin malabsorption, which i'm not sure we can even test for yet, but is a common cause of b12 deficiency.

longdom.org/open-access/foo...