There is a long list of problems indicated by a positive ttg IgA but remember that the ttg IgA is up to 95% specific to celiac - meaning if 100 people have a positive ttg IgA, 95 of them will be celiacs. I have seen (somewhere) that the specificity of ttg to celiac is as low as 75% but i can't find that info again...The following link discuses the ttg test:
I agree that it is more specific to Celiac than any other disease but there is a point to looking at it by a patient by patient basis. Theoretically 95 out of 100 patients with elevated TTG have Celiac but the University of Chicago used these theories to also swing the ball the other way:
"tTG are thought to be 97-98% specific, but by definition this means that 3 in 100 persons who don’t have celiac disease will have elevated tTG (biological variations, nothing more). If you consider that celiacs are 1% of the general population, it follows that out of 100 persons tested for tTG: 1 has celiac disease and 3 do not. This could mean that only 1 out of 4 of those with positive antibodies will have celiac disease as the cause." - http://www.curecelia...luten-free-diet
The study you read with 75 percent specificity may have come from me, I had an article on hospitalized patients with life threatening infections/conditions not related to Celiac and although they did end up finding some undiagnosed Celiac they also saw high elevations during hospital stay. These antibodies also respond to inflammation, I recall talking to a surgeon at a dinner gathering once and he brought up how they use some specific autoantibodies to help them know how the surgery went. For example, people undergoing intestinal removal and receiving ostomy bags have a high rate of elevated TTG.