Measurement of thyrotropin receptor antibodies (TRAK) with a second generation assay in patients with Graves’ disease

Abstract

Summary Aim: The detection of TSH-receptor-antibodies (TRAb) in patients (pts) with Graves’ disease (GD) is routinely used in nuclear medicine laboratories. It is performed by commercial, porcine radioreceptorassays (RRA) measuring TSH binding inhibitory activity. A second generation assay using the human, recombinant TSHreceptor was developed during the last years. The manufacturer composed this new assay as a coated tube RRA (CT RRA) and claimed a higher sensitivity for GD. Methods: TRAb was measured in 207 pts with various thyroid disorders and 205 healthy controls using the new coated tube RRA (Fa. B.R.A.H.M.S. Diagnostica GmbH, Berlin, Germany) as well as a conventional RRA (Fa. Medipan Diagnostica GmbH, Selchow, Germany): 60 pts suffering from GD showing a relapse after antithyroid drug treatment and before radioiodine therapy, 109 pts with disseminated autonomia (DA) and 38 pts suffering from Hashimoto’s thyroiditis. A ROC-analysis was performed to find the optimal decision threshold level for positivity. Results: We found 42/60 TRAbpositive pts with GD in the established RRA (threshold 6 U/L) and 52/60 in the CT RRA, respectively. The sensitivity increased from 70% (RRA) to 86,7% (CT RRA). The CT RRA found 2 false positives (one Hashimoto’s and one healthy control) and the RRA detected 3 Hashimoto’s and 2 healthy controls as false positive. Conclusion: The increased sensitivity of CT RRA for GD provides an advantage compared to conventional RRA, especially in GD-patients relapsing after antithyroid drug treatment. Functional sensitivity and Interassayvariation of CT RRA are very precisely compared to conventional RRA. Handling of the new assay is also improved.