Evaluation of the 2nd generation radio-receptional assay for anti-TSH receptor antibodies (TRAb) in autoimmune thyroid diseases. Comparison with 1st generation and anti-thyroperoxidase antibodies (AbTPO).

BACKGROUND: The detection of autoantibodies to the TSH-receptor (TRAb) by radio-receptor assays (RRA) is widely requested in clinical practice for the diagnostic workup of Graves' disease and its differentiation from diffuse thyroid autonomy. Additionally, TRAb measurement can be useful during antithyroid drug treatment of Graves' disease to evaluate the risk of relapse after therapy discontinuation. Nevertheless, some patients affected by Graves' disease are TRAb-negative when 1st generation assay is used. METHODS: In this study we evaluated the diagnostic performance of a newly developed 2nd generation TRAb assay (TRAK human DYNOtest, BRAHMS Diagnostica GmbH, Berlin, Germany) in 74 untreated patients affected by Graves' disease, 53 untreated patients affected by Hashimoto's thyroiditis and 88 patients affected by euthyroid nodular goiter. We also compared the new TRAb assay with the 1st generation test (TRAK Assay, BRAHMS Diagnostica GmbH, Berlin, Germany) and anti-thyroperoxidase assay (AbTPO DYNOtest, BRAHMS Diagnostica GmbH, Berlin). RESULTS: The 2nd generation TRAb assay showed the better diagnostic sensitivity in Graves' disease (97%) with respect to the 1st generation assay (85%) and AbTPO assay (64%). The AbTPO assay was positive in 50 of 53 (94%) patients affected by autoimmune thyroiditis. The 1st and 2nd generation TRAb assays were positive in 4 (7%) and 7 (13%) of 53 patients affected by autoimmune thyroiditis, respectively. No patients affected by nodular goiter showed positive 1st and 2nd generation TRAb assay while AbTPO levels were positive in 8 of 88 patients (specificity 91%). CONCLUSIONS: In conclusion, the 2nd generation TRAb assay is clearly more sensitive than the 1st generation test and should be used in clinical practice to minimize the incidence of TRAb-negative Graves' disease. Long term prospective studies are needed to evaluate the prognostic role of 2nd generation TRAb assay in Graves' disease. The assay of AbTPO is the best marker for autoimmune thyroiditis but is clearly less sensitive than 1st and 2nd generation TRAb assays in Graves' disease. Consequently, AbTPO assay should not be performed in Graves' disease neither alone or in association with TRAb.