Utility of TSH Receptor Antibodies in the Differential Diagnosis of Hyperthyroidism in Clinical Practice.

Graves' disease (GD) is the most common cause of hyperthyroidism in iodine-sufficient areas. It is important to distinguish GD from other causes of hyperthyroidism for optimal management. Thyroid stimulating hormone receptor antibody (TRAb) test is a commonly used test for this purpose. However, the sensitivity for this test in routine clinical practice may be affected by various factors leading to fallacies in diagnosis. Materials and Methods: A retrospective study was performed to assess the utility of an automated electrochemiluminescence TRAb immunoassay (Roche) in differentiating GD from non-Graves' disease (NGD) in routine clinical practice. Results: In 227 subjects, 146 had GD and 81 had NGD. Total T3, Total T4, Free T4, and TRAb were significantly higher in people with GD in comparison to NGD. The area under the receiver operating characteristics (ROC) curve for the assay was 0.96 (95% CI: 0.926 to 0.984, P < 0.0001). The optimal threshold for the test derived from the ROC was 3.37 IU/L, which is more than the cut-off of 1.75 IU/L suggested by the manufacturer. The sensitivity/specificity of TRAb in the diagnosis of GD at presentation was 98.4%/62.9% at 1.75 IU/L and 91.2%/90.12% at 3.37 IU/L, respectively. Conclusion: The TRAb test is a sensitive test to differentiate between subjects with GD and NGD presenting with hyperthyroidism. However, the cutoff (1.75 IU/L) as per the kit manufacturer may lead to a lower specificity for diagnosis. A modified cut-off of 3.37 IU/L should be considered for optimizing the diagnostic efficacy of the test.