Endocrine Abstracts

Background: Thyrotropin receptor (TSH-R) blocking autoantibodies (TBAb) are present in 10-15% of patients with autoimmune thyroid disease (AITD). TBAb are functional and clinically relevant. This multicenter study compares the sensitivity and specificity of five immunoassays for the measurement of TBAb and introduces a novel and ultra-rapid TBAb bioassay.

Methods: Serum samples from AITD patients were tested with two TSH-R binding immunoassays (Cobas e411, Roche and ALINITY I, Abbott), an established cell-based TBAb reporter bioassay (Thyretain®, QuidelOrtho) with expression of a Luciferase transgene as readout and a new ‘TurboTM’ TBAb bioassay (QuidelOrtho) 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 stimulatory TSH-R-Ab (TSAb, Thyretain®).

Results: Of 1011, unselected, consecutive AITD patients (Graves’ disease and Hashimoto’s thyroiditis), 131 patients and 212 samples were TBAb positive. Median age was 33 years (25/75 percentile 13/48 years) and female: male ratio was 2.9:1. Of 212 samples, 149 (70.3%), 47 (23.1%) and 16 (7.5%) were hypothyroid, euthyroid and hyperthyroid, respectively. Thyroperoxidase and thyroglobulin autoantibodies were present in 136 (64.2%) and 70 (33%) samples, respectively. The five TSH-R-Ab assays were negative in 90 control subjects devoid of autoimmune thyroid and endocrine disorders. In contrast, the TurboTM cAMP TBAb, Luciferase TBAb and the binding assays detected TBAb in 212 (100%), 168 (79%) and 138/180 (65.1%) samples, respectively (Chi-square test P < 0.001). The TurboTM TBAb bioassay highly correlated with thyroid function (P = 0.007). Furthermore, the magnitude of percentage inhibition in both TurboTM 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 11 (5.2%) samples showed dual positivity for TSAb and TBAb in all four bioassays. The two TBAb bioassays positively correlated (Spearman’s r =0.8, P < 0.001). All bioassay measurements were done in duplicate. Intra-assay validation demonstrated adequate precision at 92% and 44% inhibition (serum TBAb positivity) with very low (3.95% inhibition) and low (6.5% inhibition) standard deviation (SD), respectively. Inter-assay validation showed 92% and 44% inhibition with SD of 7.1% and 4.9% inhibition, respectively.

Conclusions: This is the largest reported collective of TBAb-positive samples in AITD. TBAb markedly affects thyroid function. The easy-to-perform TurboTM blocking bioassay detected significantly more TBAb than the established immunoassays demonstrating higher analytical performance and clinical utility in the management of AITD patients.