Antibodies to TSH-Receptor
Thyrotrophin receptor antibody assays (TRAb) have become readily available, and a positive result strongly supports the diagnosis of Graves’ disease. Determination of TRAb is not required for the diagnosis, but the implied specificity of a positive test provides security in diagnosis, and for this reason the assay is now widely used. The assay is valuable as another supporting fact in establishing the cause of exophthalmos, in the absence of thyrotoxicosis, and high maternal levels predict fetal or neonatal thyrotoxicosis. Measurement of TRAb (TSH-R binding antibodies), any antibody that binds to the TSH-R, is generally available.Assays for Thyroid Stimulating Antibodies (TSAb,TSI) are less available, but are more specific for the diagnosis. Using current tests, both are positive in about 90% of patients with Graves disease who are thyrotoxic. “Second generation” assays becoming available use monoclonal anti-TSH-R antibodies and biosynthetic TSH-R in coated tube assays, are reported to reach 99% specificity and sensitivity. Although rarely required, serial assays are of interest in following a patient’s course during antithyroid drug therapy, and a decrease predicts probable remission.