Evaluation of analytic and clinical performance of two immunoassays for detecting thyroid‐stimulating receptor antibody in the diagnosis of Graves’ disease

OBJECTIVE: To evaluate the analytical and clinical performance of two immunoassays for diagnosis of Graves’ disease (GD), the Immulite thyroid‐stimulating immunoglobulin (TSI), and Elecsys Anti‐TSH receptor (TSHR) assay. METHODS: Precision and analytical measurement range were assessed using pooled samples of patients. The comparison between the two methods was evaluated using 579 clinical samples, and receiver operating characteristic (ROC) curves were drawn using the final diagnosis as reference. Clinical sensitivity and specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) were calculated for the two tests. RESULTS: The repeatability and intermediate imprecision coefficient of variation (CV%) of the TSI assay were 3.8% and 4.1% at 0.95 IU/L, and 3.5% and3.6% at 19.5 IU/L, respectively. The assays were linear over a range 0.27–38.5 IU/L. There was a high correlation between the quantitative results of the two methods (correlation coefficient r = 0.930). The cut‐off value obtained by ROC analysis for TSI assay was 0.7 IU/L with sensitivity of 93.7% and specificity of 85.1%. An overall qualitative agreement of 91.5% between two methods was observed. Among 44 patients with discordant qualitative results, the TSI assay provided more satisfactory results consistent with clinical diagnoses. CONCLUSION: The TSI assay showed excellent analytical performance and provided a high PPV for GD.