Certain blood tests may confirm a suspicion of celiac disease. Primary among these is the highly reliable and automated test for antitransglutaminase antibodies (antitTG) of the IgA class. An equally effective, though less widespread, test is for anti-endomysial antibodies (EMA). Tests for antigliadin antibodies (AGA) of the IgA and IgG classes are particularly conclusive in children under the age of three. An isolated change in AGA-IgG does not generally carry diagnostic weight except in children with a deficiency in serum IgA.
In the event that the blood tests are positive, the next step is to perform an intestinal biopsy, a procedure in which a tissue sample from the small intestine is taken by means of an endoscope and then analysed. If the characteristic alterations in the intestinal lining (atrophy of the villi and an increase in intraepithelial lymphocytes) are found, a definitive diagnosis of the celiac disease can be made.
The gluten challenge
In cases of doubt, it is customary to carry out a gluten challenge, which involves re-exposing the subject to gluten after at least two years of dietary treatment. The diagnosis of celiac disease is confirmed if the test, which is done under medical supervision, causes a clinical and histological relapse within a span of several months or, rarely, over a period of years.