7007 Analytical & Clinical Performance of a Novel Sensitive Rapid Bioassay for Thyrotropin Receptor Antibodies

Abstract Disclosure: P.D. Olivo: Consulting Fee; Self; QuidelOrtho, CA USA. H. Kim: Employee; Self; QuidelOrtho. L. Miao: Employee; Self; QuidelOrtho. J. Houtz: Employee; Self; QuidelOrtho. M. Luffy: None. J. Wolf: None. G.J. Kahaly: Grant Recipient; Self; QuidelOrtho, USA. Background: The role of stimulatory anti-TSH-R-Ab in the pathogenesis of autoimmune hyperthyroidism is well established. A novel and rapid cell-based bioassay, referred to as Turbo TSITM, for measurement of thyroid-stimulating autoantibodies (TSAb) was recently developed. An assessment of the analytical & clinical performance of this bioassay is described herein. Methods: Turbo TSI greatly reduces the complexity and time required to measure TSAb. It avoids the need for cell culture, has no wash or lysis steps, and has a total turn-around-time of less than 90 minutes. Thawed cells from Turbo TSI kits were treated with different concentrations of a World Health Organization (WHO) international standard (IS) TSI or TSAb-positive serum. TSAb was measured as a function of luciferase activity measured as relative light units (RLU) and converted into international units per liter (IU/L). Two users at two sites performed analytical performance studies on numerous samples, over multiple days. Results: The limit of blank, limit of detection and limit of quantitation were determined to be 0.007 IU/L, 0.014 IU/L, and 0.021 IU/L, respectively. Receiver operator characteristics (ROC) analysis determined the cut-off to be 0.0241 IU/L with an area under the curve of 0.984. The linear range was shown to be from 0.015 to 11.958 IU/L. The intra-laboratory precision was ≤15 percent CV. The overall reproducibility of the assay was ≤20 percent CV for five concentrations (0.06 to 5.16 IU/L). Interference and cross reactivity studies with a variety of substances showed that the assay was robust. Turbo TSI demonstrated 95.2% (95% CI 83.3-98.1) sensitivity and 94.8% (95% CI 90.9-97.1) specificity when compared with an FDA-cleared bioassay (Thyretain® TSI) using serum from 295 patients with autoimmune thyroid disease (AITD). When testing 172 unselected, consecutive TSAb+ AITD patients, a US based, prospective, multicenter, blinded study showed a 98% concordance between Turbo TSI and Thyretain® TSI. When comparing Turbo TSI, Thyretain TSI and a TSH-R-Ab binding immunoassay (Cobas) in 670 unselected, consecutive, treated and untreated AITD subjects, sensitivity was 83%, 79% and 68%, respectively (Turbo vs. Cobas, P<0.001). Furthermore, testing 84 patients with naïve, untreated Graves’ hyperthyroidism, detection of TSH-R-Ab was 100%, 98% and 92%, respectively (Turbo TSI vs binding assay, P<0.01). Finally, 95% vs. 73% of 332 patients with Graves’ orbitopathy were TSH-R-Ab+ with Turbo TSI vs. binding assay (P<0.001). Conclusions: The Turbo TSI bioassay exhibits excellent analytical & clinical performance, a high level of reproducibility, and compares well with the FDA-cleared Thyretain® TSI. Presentation: 6/1/2024