The Tissue Transglutaminase (TTG) Antibody, IgA (CLIA) test is used to help diagnose celiac disease, an autoimmune condition in which the body reacts to gluten. It detects the presence of IgA antibodies against the enzyme tissue transglutaminase, which are often elevated in people with celiac disease. This test is highly sensitive, reliable and commonly used as the first step in screening for celiac disease.