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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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The only symptom I know of that is celiac for certain is dh, which must be diagnosed by a dermatologist.

I have both eoe and celiac and now that I have been gluten free for 18 months, my anemia is gone. It is good to get off the iron supliments because mine may have been the cause of my ulcers. It feels good to recover and heal! I may work my way down to fewer supliments and lots of feel great da...

Your daughter does not have a strong positive. I suspect that the GI might do as RMJ suggested which would be to load her up on gluten for six months and retest. On the other hand, with a diagnosed sibling and a very mild positive, your GI might recommend the endoscopy or run the test again to ...

I was diagnosed with celiac last year on an endoscopy looking for the cause of my anemia. At the time, my GI doc tested m for EoE and it was negative. Fast forward 11 months, I developed sudden heart burn, dysphagia out of the blue. My doc thinks it's EoE. Biopsy was last week and I am still wait...

No, the control test is to verify that she will react to that particular type of test. If she didn't, then certain of the bloods would not be applicable to her. They would be false negatives. As far as tests being weak positives, that's like being a little pregnant. A positive is a positive....