Stability of TSH receptor antibody concentrations and comparability of its immunoassays.

Background And Aims: Graves' Disease (GD) is an autoimmune form of hyperthyroidism where autoantibodies are directed against the TSH-receptor (TSH-receptor antibodies; TRAb). GD is suspected if TRAb concentrations are above a pre-specified cut-off value. TRAb concentrations are measured using immunoassays. This study aimed to compare the performance of the recently implemented Alinity immunoassay to the KRYPTOR and Cobas TRAb immunoassays.

Materials And Methods: Left-over serum samples in which TRAb concentrations were measured (KRYPTOR) were used. First, TRAb stability at -20 °C for four to six years and up to five freeze-thaw cycles were assessed. Second, TRAb measurements (n = 436) were repeated using the Alinity and Cobas immunoassay and results (scored as positive/negative based on cut-off value) were compared.

Results: TRAb results were stable over five years and up to five freeze-thaw cycles. When comparing immunoassays, 86.2% of the results were similar. Total discrepancy differed between the immunoassays (5.4% Cobas vs Alinity, 8.8% Alinity vs KRYPTOR, 13.3 % Cobas vs KRYPTOR). The KRYPTOR immunoassay showed more negative TRAb results than Cobas and Alinity.

Conclusion: The Alinity immunoassay showed comparable TRAb results, even though slightly more positive results compared to the KRYPTORand slightly more negative results compared to the Cobas immunoassay were seen.