Thyrotropin Receptor Antibody Assays

In this issue of the Journal, Leschik and colleagues1 compare the analytical performance and the clinical utility of a commercially available thyroid-stimulating immunoglobulin (TSI) reporter bioassay with an automated thyrotropin-binding inhibitory immunoglobulin (TBII) electrochemiluminescent immunoassay. The TSI reporter bioassay is a cell-based assay (or “bioassay”) that uses a genetically engineered cell line capable of specifically detecting serum TSI using cyclic AMP–dependent luciferase activity as the readout. The TBII assay is an anti–thyrotropin receptor (TSHR) electrochemiluminescent immunoassay that uses a porcine TSHR and human anti-TSHR autoantibody M22. The authors report that the TSI bioassay is able to detect lower levels of anti-TSHR autoantibodies than the TBII assay and exhibits better precision, but they do not present data indicating whether either assay is more predictive than the other in determining patients’ responses to antithyroid treatment. However, they clearly establish the sensitivity of both assays. TSHR autoantibody (TRAb) measurements (as either TSI or TBII) generally have few potential clinical applications: confirming the diagnosis of Graves disease, the prediction of risk for Graves disease in a neonate born to a mother with Graves disease in pregnancy or in the past, and the prediction of relapse in the medical treatment of Graves disease.