Evaluation of the diagnostic performance of thyroid‐stimulating immunoglobulin and thyrotropin receptor antibodies for Graves' disease

OBJECTIVE: To evaluate thyroid‐stimulating immunoglobulin (TSI) and thyrotropin receptor antibodies (TRAb) diagnostic performance for Graves' disease (GD) and determine clinical cut‐off value for diagnosing GD. METHODS: Of 1369 retrospectively enrolled subjects, 1364 had a definitive diagnosis of untreated GD (GD‐UT, n = 87); treated GD (GD‐T, n = 206); autoimmune thyroid disease (AIT, n = 241); thyroid nodules (TN, n = 677); subacute thyroiditis (ST, n = 28); healthy subjects (HS, n = 125); other diseases with serological hyperthyroidism (n = 5) and were grouped into the following: UT‐GD and control groups (AIT, TN, ST, and HS); and UT‐GD and non‐GD hyperthyroidism groups. Diagnostic performance of TSI and TRAb was evaluated using area under the curve (AUC) of receiver‐operating characteristic (ROC) curve, and optimal clinical cut‐off value was determined using maximization of Youden index. RESULTS: TRAb AUC and clinical cut‐off value for diagnosing GD were 0.981 and 1.245 IU/L (sensitivity, 96.6%; specificity, 97.1%; positive predictive value [PPV], 71.8%; negative predictive value [NPV], 99.9%; positive likelihood ratio [PLR], 33.31; negative likelihood ratio [NLR, 0.035), respectively, for the GD‐UT and control groups. Those for TSI were 0.992 and 0.467 IU/L (sensitivity 98.8%; specificity, 96.4%; PPV, 68.8%; NPV, 99.9%; PLR, 27.472; NLR, 0.011). Those for TRAb in GD‐UT and non‐GD hyperthyroidism groups were 0.923 and 1.78 IU/L (sensitivity, 92.0%; specificity, 89.1%; PPV, 93%; NPV, 87.5%; PLR, 8.44; NLR, 0.089), respectively. For TSI, these were 0.92 and 0.545 IU/L (sensitivity, 97.7%; specificity, 83.6%; PPV, 90.4%; NPV, 95.8%; PLR27.472, NLR, 0.011), respectively. CONCLUSION: TSI diagnostic performance for GD was excellent and had better sensitivity than TRAb.