FRI537 Thyrotropin Receptor Blocking Antibodies - A Multicenter, 4-Assay Comparison

Disclosure: A. George: None. A.T. Bossowski: None. B. Hatun: None. J. König: None. M.A. Lupo: None. L. Frommer: None. J. Wolf: None. G.J. Kahaly: None. Background: Thyrotropin receptor (TSH-R) blocking autoantibodies (TBAb) are present in 10-15% of patients with autoimmune thyroid disease (AITD). TBAb are functional, impact thyroid function, and are clinically relevant. This multicenter study compares, in a large collective of AITD subjects, the sensitivity and specificity of four immunoassays for the measurement of TBAb and introduces a novel and ultra-rapid TBAb bioassay. Methods: Serum samples from AITD patients were tested with a TSH-R binding immunoassay (Cobas e411, Roche, Penzberg, Germany), an established cell-based TBAb reporter bioassay (Thyretain®, Quidel, San Diego, USA) with expression of a Luciferase transgene as readout and a new “Turbo(TM)” TBAb bioassay (Quidel) with a readout that is based on a cyclic AMP-activated luciferase. A Passing-Bablok regression and intra- and inter-assay validations were performed. All samples were also tested for stimulating TSH-R-Ab (TSAb, Thyretain®, Quidel). Results: Of 1011, unselected, consecutive AITD patients (Graves’ disease and Hashimoto thyroiditis), 132 patients and 212 samples were TBAb positive. Median age was 32 years (25/75 percentile 13.25/46.5 years) and female: male ratio was 2.86:1. Of 212 samples, 149 (70.3%), 47 (23,1%) and 16 (7,5%) were hypothyroid, euthyroid and hyperthyroid, respectively. Thyroperoxidase and thyroglobulin antibodies were present in 136 (64.15%) and 70 (33.02%) samples, respectively. The four TSH-R-Ab assays were negative in 90 control subjects devoid of autoimmune thyroid and endocrine disorders. In contrast, the Turbo(TM) cAMP TBAb, Luciferase TBAb and the Cobas binding assays detected TBAb in 212 (100%), 168 (79%) and 137/180 (76%) samples, respectively (Chi-square test p<0.001). The Turbo(TM) TBAb bioassay highly correlated with thyroid function (p=0.007). Furthermore, the magnitude of percentage inhibition in both Turbo(TM) and Luciferase TBAb bioassays correlated with TSH-R-Ab binding assay positivity (both p<0.001). Seventeen of 212 (8%) samples showed dual TSH-R-Ab positivity in the Turbo TBAb and TSAb bioassays, while 13 (6.1%) samples showed dual positivity for TSAb and TBAb in all three bioassays. The two TBAb bioassays correlated (Spearman’s r =0.59, p< 0.001). Single-user testing and intra-assay validation demonstrated adequate precision with very low coefficient of variation (CV 0.05) and low CV (0.14) at 92% and 44% inhibition (serum TBAb positivity), respectively. Conclusions: This is the largest reported collective of TBAb-positive samples in AITD patients, measured with four different immunoassays. TBAb markedly affects thyroid function. The novel, easy-to-perform, rapid and reliable Turbo(TM) blocking bioassay detected significantly more TBAb than the established immunoassays demonstrating both its higher analytical performance and clinical utility in the management of AITD patients. Presentation: Friday, June 16, 2023