Thanks :). There are two test (I know of): a blood test that looks for gluten antibodies (this one can sometimes give a false negative), and an intestinal biopsy (100% accurate). In any case, is extremely important that you don’t go in a gluten free diet beforehand, to avoid masking the symptoms. I mean, a celiac with a perfect diet, won’t have antibodies nor damage in the interstines, making boths test useless.