US-based, Prospective, Blinded Study of Thyrotropin Receptor Antibody in Autoimmune Thyroid Disease

Abstract Context Bioassays provide information on the functionality of thyrotropin receptor antibodies (TSH-R-Ab) and thus may offer more clinical utility than binding assays. Objective In this prospective, blinded, US-based study, the clinical performance of several TSH-R-Ab assays was compared. Setting US endocrinology clinic. Subjects One hundred sixty-two unselected, consecutive, well-documented patients with various thyroid diseases and healthy controls. Intervention(s) Blinded TSH-R-Ab measurements. Main Outcome Measure(s) Sensitivity and specificity of 4 TSH-R-Ab assays. Results The 4 TSH-R-Ab assays were negative in all 42 patients without autoimmune thyroid disease (AITD). In 104 patients with Graves’ disease (GD), irrespective of the disease duration, TSH-R-Ab positivity was present in 65 (63%), 67 (65%), and 87 (84%) for the Cobas and Immulite binding assays and stimulatory TSH-R-Ab [thyroid-stimulating immunoglobin (TSI)] bioassay, respectively (TSI vs Immulite P < .0025, TSI vs Cobas P < .0009). Fifteen newly diagnosed GD patients were all positive in the TSI bioassay, but only 11 (73%) were positive in the Cobas and Immulite binding assays. Nine GD patients with biochemical subclinical hyperthyroidism were TSI-positive but Immulite- and Cobas-negative. Two GD patients were blocking TSH-R-Ab [thyroid-blocking immunoglobin (TBI)]-positive and TSI-negative, and the Immulite and Cobas were positive in both. Additional serum samples from AITD patients that consisted of 30 TBI-positive and 10 TSI-positive samples were blindly tested in the binding assays. Only 6 of the 10 TSI-positive samples were positive in both binding assays, and 30 and 28 of the TBI-positive samples were positive in the Cobas and Immulite assays, respectively. Conclusion Binding TSH-R-Ab assays are less sensitive than TSI bioassays and are not specific for stimulating antibodies. Measuring the function of TSH-R-Ab in a bioassay can provide useful information to clinicians.