For children and adolescents with strong clinical suspicion for celiac disease, repeated transglutaminase-2-IgA (TG2-IgA) levels that are more than 10 times higher than the upper limit of normal often suffices for diagnosis, according to an American Gastroenterological Association clinical practice update and expert review.
This approach precludes the need for esophagogastroduodenoscopy (EGD) in about 30%-50% of cases, wrote Steffen Husby, MD, PhD, of Odense University Hospital (Denmark), together with his associates in. “When such a strongly positive TG2-IgA is combined with a positive endomysial antibody in a second blood sample, the positive predictive value for celiac disease is virtually 100%.” But for adults, they recommend confirmatory histologic analysis of duodenal biopsies with Marsh classification, counting of lymphocytes per high-power field, and morphometry.
Transglutaminase-2 is the major autoantigen present in celiac disease and can now be assessed with accurate, convenient, high-throughput tests, such as enzyme-linked immunosorbent assays. To maximize test TG2-IgA accuracy, Dr. Husby and his associates recommend testing patients who have compatible signs and symptoms of celiac disease or are asymptomatic but have other risk factors, such as confirmed autoimmune diseases (type 1 diabetes, autoimmune thyroid or liver diseases), chromosome abnormalities (Down or Turner syndrome), or first-degree relatives with celiac disease.
Several other serologic tests are available but have a more limited role in diagnosing celiac disease, according to the practice update. Perhaps most useful is the endomysial antibody (EMA) test, which evaluates tissue-bound TG2-IgA. This test is highly specific but labor-intensive and user-sensitive and thus is best used to confirm a positive TG2-IgA result. Deamidated gliadin peptide antibody assays are less accurate than TG2-IgA, while HLA-DQ2/DQ8 testing is best reserved for cases where the diagnosis is complicated by a prior gluten-free diet or inconclusive antibody titers or histology.