Comparison of three competitive immunoassays for measurement of TSH receptor antibodies in patients with Graves' disease.

Thyrotropin (TSH) receptor antibodies (TRAb) mediate the hyperthyroidism of Graves' disease (GD). The aim of the study was to compare the diagnostic performance and assay agreement between three immunoassays for the measurement of TRAb in patients with newly diagnosed GD. TRAb was measured with three different assays [H-TRAb (BRAHMS Diagnostica), M22-Man (RSR Limited) and M22-Aut (Roche Diagnostics)] in 387 participants who were recruited from two Danish population-based studies and diagnosed with GD (n = 101), multinodular toxic goitre (n = 88), primary autoimmune hypothyroidism (n = 100) or included as controls (n = 98). Coefficient of variation for duplicate measurements with each of the three assays were H-TRAb: 3.6%, M22-Man: 9.4%, M22-Aut: 7.7%. Frequency of TRAb positivity in patients with GD were H-TRAb: 95%, M22-Man: 94%, M22-Aut: 96%. Receiver operating characteristic analysis revealed a high sensitivity (H-TRAb: 95%, M22-Man: 93%, M22-Aut: 95%) and specificity (H-TRAb: 99%, M22-Man: 99%, M22-Aut: 97%) for the diagnosis of GD with all assays. Comparison of TRAb levels showed inter-assay variability and values were considerably lower with the M22-Man assay. All TRAb assays showed a high diagnostic performance for GD, but a high inter-assay variability was observed limiting the use of different assays in clinical monitoring of patients with GD.