Anti-thyroglobulin antibodies in patients with autoimmune thyroid disease interfere in thyroglobulin immunoassays and, depending upon the assay, may result in falsely low or elevated levels.8 Autoantibodies against T4 and T3 have also been reported, although they are uncommon.4 In one-step competitive immunoassays in which all the reagents are mixed, the autoantibodies bind to the labelled thyroid hormone analogue and less labelled analogue binds to the capture antibody. This evidence concerns the gene TG and autoimmune thyroid disease.