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Abstract
Introduction: In recent years, different non-competitive immunoassays have been developed for the measurement of anti-TSH receptor antibodies (TRAbs), the main autoantigen of Graves’ Disease (GD). The aim of this study was to evaluate the analytical and clinical performance of two non-competitive methods for TRAbs measurement, in patients with and without GD. Materials and Methods: Serum samples were evaluated in a retrospective, observational, cross-sectional study. TRAbs were measured using Maglumi (Snibe) and TSI Immulite(Siemens). Pearson’s correlation coefficient, Bland-Altman plot analysis, Passing- Bablok regression, and kappa coefficient were determined. ROC curve analysis was determined for diagnostic validity. Results: The Pearson linear correlation coefficient was 0.93 (p= <0.0001). The Bland- Altman plot demonstrated a mean difference of 0.69. The Passing-Bablok regression proved the presence of constant and proportional differences between methods. The kappa was 0.59. The sensitivity of TSI Immulite was 84.6%, whereas that of Maglumi was 57%. Discussion: The methods demonstrated excellent correlation and acceptable diagnostic concordance with good sensitivity and specificity for the diagnosis and monitoring of GD. However, the methods are not interchangeable. Monitoring should be done using the same methodology. TSI Immulite detected a higher percentage of positive samples than Maglumi. Low concentration of thyroid-stimulating immunoglobulin was found in patients with GD in remission. It would be necessary to research a prognostic cut-off value for remission before suspension of antithyroid drugs in this population.
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