THYROID

TSH Receptor Antibody (TRAb)

There is convincing evidence that antibodies to the TSH receptor (TRAb) are responsible for Graves' hyperthyroidism. These antibodies are detectable in approximately 90% of untreated Graves' patients when measured by receptor assays. The presence of TRAb indicates that the patient's thyrotoxicosis is of autoimmune etiology rather than due to toxic nodular goiter. Because the form of treatment for Graves' disease may differ from the treatment of other forms of thyrotoxicosis, an initial TRAb measurement is clearly of value.

Additionally, TRAb levels tend to fall during antithyroid drug treatment for Graves' disease. The absence of antibodies after a course of drug therapy may indicate disease remission, and the withdrawal of therapy can be considered. If TRAb are still present after a course of antithyroid drugs, the risk of relapse is high, and surgery or radioiodine therapy can be considered.

The measurement of TRAb by receptor assay provides a rapid, sensitive, specific and inexpensive diagnostic marker for Graves' disease.