So, how do we diagnose coeliac disease? Well, the gold standard method would simply be to take a piece of the small intestine out and give it to the pathologists. This would be accomplished by means of endoscopy. Coeliac disease generates a particular histological picture, with villous atrophy, crypt cell hyperplasia and a lymphocytic infiltrate. Although highly suggestive, this profile is not unique to coeliac disease, but what really clinches the diagnosis is if this pathological histological picture resolves once the patient stops eating any gluten.
OK, that's all very well, of course, but sending every person with bloating for an endoscopy is a bit silly. Fortunately, there are also several serological tests that one can do, with excellent sensitivity and specificity. All of these blood tests measure an IgA antibody to a particular small bowel antigen, and include antigliadin, antiendomysial and anti-tissue transglutaminase. (Tissue glutaminase is the enzyme responsible for modifiying the gliadin in the intestine.) These antibodies, if present, should also resolve on elimination of gluten from the patient's diet.
So the bottom line is this: on history or examination, you can usually only get as far as to say that you might be dealing with gluten enteropathy. If this is the case, the usual next step is to do the blood tests. Should they come back positive, an endoscopic biopsy of the duodenum is warranted. Both of the latter two pathological indicators should resolve on a gluten-free diet in order to clinch the diagnosis.