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Tests for IgA Antibodies to Tissue Transglutaminase Vary Too Much For Easy Commutability

Celiac.com 08/26/2015 - People with IgA antibodies to tissue transglutaminase (anti-tTg) likely have a higher risk for celiac disease. Some clinicians and researchers have suggested that common multiples of the upper limit of normal (ULN) be useful tool in improving diagnostic pathways, as well as continuity between tests.

Photo: CC--Alexandre DulaunoyHowever, a new study suggests that both sensitivity and specificity of tests for IgA antibodies to tissue transglutaminase vary widely by individual kit, and that their test values are not easily commutable using common multiples of the ULN to correct for inter-assay variations. Commutability just means the ability to make sure that two different tests really are equal. If results of different tests are commutable, it means that they are equal. In this case, the term applies to test results for various representative samples from healthy and diseased individuals.

For the study, the research team recently looked at the use of immunoassays for the detection of IgA antibodies to tissue transglutaminase, and also sought to better understand of the significance of multiples of the upper limit of normal and inter-assay correlations. The research team included B.B. Suh-Lailam, K.W. Davis, and A.E. Tebo. Using indirect immunofluorescence assay (IFA) as reference, the team assessed characteristics of four anti-tTG IgA assays relative to endomysial IgA (EMA).

They also assessed commutability between anti-tTG immunoassays and/or EMA based on manufacturer's recommended cut-off values and three common multiples of ULN (3×, 5× and 10×). To do this, they analyzed samples from 200 patients and 100 healthy individuals.

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They found that, at manufacturer's cut-off, the sensitivities for the tTG assays ranged from 72.5% to 98.6% and specificities from 60.3% to 99.2%. The percent positive agreements between any anti-tTG and EMA or any two anti-tTG immunoassays varied from 56.7% to 98.0% and 46.7% to 100.0%, respectively.

At 3×, 5× or 10× ULNs, the inter-rater reliability as measured by Cohen κ between any two anti-tTG assays were quite variable and ranged from 0.28 to 0.96, 0.26 to 0.89 or 0.13 to 0.78, respectively.

Furthermore, the percent positive agreements between any two anti-tTg IgA immunoassays ranged from 83.1% to 98.2%, 92.0% to 100%, or 100%, at 3×, 5× or 10×, respectively.

Hence, the team's basic takeaway that result parameters for tTG IgA immunoassays or tTG IgA and EMA vary by kit, and thus common multiples of the ULN are not enough to correct for variation between tests.

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It took me 20 years or more Barry so I wouldn't claim any great insight on this I had a 'eureka' moment, up until then I was walking around with multiple symptoms and not connecting any dots whatsoever. It is very, very difficult to diagnose and that's something that's reflected in so many of the experiences detailed here. A food diary may help in your case. It helped me to connect the gaps between eating and onset. It could help you to track any gluten sources should you go gluten free. It is possible for your reactions to change over time. As to whether its celiac, that's something you could explore with your doctor, stay on gluten if you choose to go that way. best of luck! Matt

I took Zoloft once. Loved it until it triggered microscopic colitis (colonoscopy diagnosed it). Lexapro did the same. However, I have a family member who is fiagnosed celiac and tolerates Celexa well.

Thanks for the update and welcome to the club you never wanted to join! ?

Jmg, I am glad you were able to come to the realisation that the culprit was in fact gluten. For me its not so simple. IBS runs in the family, as do several food intolerances. Its just in the last while that I can finally reach the conclusion that for me its gluten. The fact that it is a delayed effect-several hours after, made it harder. Friday I had some KFC, felt great. Saturday evening felt sleepy, Sunday felt awful and my belly was huge. I think I have gone from mildly sensitive to full blown celiac over the course of five years-if that possible. Thanks for all your help.

I thought I'd take a moment to provide an update, given how much lurking I've done on these forums the last year. It took a long time, but I've since had another gastroenterologist visit, many months of eating tons of bread, and an endoscopy where they took several biopsies. I have to say, the endoscopy was a super quick and efficient experience. During the procedure they let me know that it looked somewhat suspicious, causing them to take many biopsies, and then did comprehensive blood work. About a month later, I received a call telling me that the TTG came back positive a second time, and that the biopsies were a mix of negative (normal) results and some that were positive (showing blunting of the villi). As a result, I've been given a celiac diagnosis. It's been about a month now that I've been eating gluten free. Not sure if I'm really feeling all that different yet. It's a bit twisted to say, but in some way I was hoping for this diagnosis ? thinking how nice it would be to have an explanation, a plan of action, and feeling better. It's certainly no small change to be totally gluten free, but I'm hopeful.