Second generation assay for thyrotropin receptor antibodies has superior diagnostic sensitivity for Graves' disease

Detection of autoantibodies to the TSH receptor (TSH-R) in Graves' disease has found widespread use in clinical routine and is performed mostly by com mercial RRAs measuring TSH binding inhibitory activity. We report in this s tudy on a second generation TSH binding inhibitory assay using the human re combinant TSH-R with two major improvements: 1) superior diagnostic sensiti vity for Graves' disease, and 2) for the first time, nonradioactive and rad ioactive coated tube (CT) technology. Full-length human recombinant TSH-R w as expressed in the K562 leukemia cell line and grown in suspension at a hi gh density. A murine monoclonal antibody was selected for binding to the na tive TSH-R without interfering with autoantibodies or TSH and was coated to polystyrene tubes. After detergent extraction, TSH-R was affinity immobili zed on antibody-coated tubes. The binding of TSH to the TSH-R could be demo nstrated by the addition of I-125 or acridinium ester-labeled bovine TSH, a nd this binding could be inhibited by sera from patients with Graves' disea se up to 95%. Subsequently, these novel assays, a CT RRA and a CT luminesce nce receptor assay, were compared to the conventional RRA based on porcine antigen in a blinded clinical multicenter trial. Sera from 328 patients wit h Graves' disease (86 untreated, 116 treated, and 126 in remission) and 520 controls (comprised of healthy blood donors and patients with autoimmune d iseases or goiter) were tested in all 3 assays. Receiver-operating characte ristic plot analysis resulted in a specificity of 99.6% with a sensitivity of 98.8% for both CT assays, compared to 99.6% specificity and 80.2% sensit ivity for the conventional RRA (P < 0.001). In all 3 groups of patients wit h Graves' disease, the 2 CT assays were significantly more sensitive for th e disease than the conventional assay, without loss of specificity in the c ontrol groups. This increase in sensitivity and the nonradioactive or radio active CT format constitute a significant improvement over the currently av ailable assays.