Use of the 2nd generation TRAK human assay did not improve prediction of relapse after antithyroid medical therapy of Graves' disease.

OBJECTIVE Antithyroid drug treatment (ATD) is used world-wide in the treatment of thyrotoxicosis in patients with Graves' disease (GD). The main problem is a relapse rate of 30 to 50% within 2 years after the treatment has stopped. The measurement of thyrotropin receptor antibodies (TRAb) in serum has been used to confirm the diagnosis of GD in selected patients with a diagnostic specificity of 70 to 90%. However, in predicting the recurrence of thyrotoxicosis after discontinuing ATD it has been of little value. The aim of this study was to evaluate the ability of TRAb measured by the more sensitive recombinant human TSH receptor method to predict risk of recurrence of GD after discontinuing ATD. MATERIALS, PATIENTS AND METHODS: One hundred and twenty nine patients with newly diagnosed GD were included. Of these, 58 had relapse of hyperthyroidism in a follow-up of at least 11 months (median 18 months, range 11-49) after discontinuing ATD. In 122 Graves' patients TRAb were measured at the time of diagnosis and in all patients when discontinuing ATD by a competitive radioreceptor assay using recombinant human TSH receptors (TRAK human assay). RESULTS We found an increased diagnostic specificity (99%) compared with the old TRAK porcine assay. The predictive values of a positive and negative test in relation to the prediction of a relapse of GD were found to be only 55% and 62% respectively when using a cut-off level of 1.5 IU/l, and the predictive value of a positive test decreased to 49% and of a negative test to 60% at a lower cut-off limit (1 IU/l). CONCLUSION Our study confirms that the new TRAK human assay had a superior diagnostic sensitivity in comparison with the old TRAK porcine assay. Despite the higher diagnostic sensitivity of the TRAK human method, we could not find any improvement of predictive values for relapse of hyperthyroidism in the measurement of TRAb at the end of ATD.