Anti-transglutaminase antibodies and the serological diagnosis of coeliac disease.

Tissue transglutaminase (tTG) has recently been identified as the antigenic target recognised by anti-endomysial antibodies in patients with coeliac disease. In this study, an enzyme-linked immunosorbent assay (ELISA) is used to measure IgA, IgG and IgM antibodies to tTG in patients with coeliac disease and a variety of other inflammatory disorders; and is compared to the standard immunofluorescence test used to detect endomysial antibodies (EMA). In the samples tested, 3% control sera (n=146), 83% EMA-positive sera (n=29), 9% patients with Graves' disease (n=94), 12% antimitochondrial antibody-positive sera (n=53), 11% rheumatoid arthritis patients (n=53) and 22% systemic lupus erythematosus (SLE) patients (n=46) were positive for anti-tTG antibodies. In contrast, none of the controls, 1% of patients with Graves' disease, 2% antimitochondrial antibody-positive sera, 2% rheumatoid arthritis patients and none of the SLE patients were positive for EMA. Measurement of IgG or IgM antibodies to tTG was much less reliable than IgA anti-tTG antibody for the serological diagnosis of coeliac disease. The addition of calcium to the coating buffer improved the assay characteristics of the anti-tTG ELISA. However, the IgA anti-tTG ELISA, with and without calcium, performed less well than the standard EMA test used for the serological diagnosis of coeliac disease. In particular, the anti-tTG ELISA gave a higher rate of non-specific positive reactions.