Third generation radioimmunoassay (RIA) for TSH receptor autoantibodies (TRAb) - one step less, similar results?

TSH-receptor (TSHR)-autoantibody (TRAb) is the serological hallmark of Graves' disease (GD). Recently, 3^rd-generation radioimmunoassays (RIA) employing monoclonal TRAb such as M22 or T7 instead of TSH for the inhibition of human TRAb binding with solid-phase TSHR (coated tubes) have been introduced into laboratory routine.

As current assays typically employ a consecutive incubation of patient serum and labelled monoclonal TRAb, automation of TRAb RIA is a challenge. Thus, the assay procedure using human TSHR-coated tubes and the mouse monoclonal TRAb T7 was modified by combining both steps. The novel one-step method was compared with its corresponding consecutive 3^rd-generation RIA by investigating 304 individuals encompassing 102 patients with active GD (GD_a), 43 patients with GD after successful therapy (GD_t), 31 with Hashimoto's disease (HD), 28 with non-autoimmune thyroid diseases (NAITD) and 100 healthy subjects (HS).

With the new method, the incubation time was shortened by approximately one hour. Both 3^rd-generation RIAs did not reveal a significantly different assay performance by comparing areas under the curve (AUC) with receiver operating characteristics curve analysis (AUC one-step: 0.94, AUC two-step: 0.96, p > 0.05, respectively). The two-step TRAb RIA demonstrated sensitivity and specificity values of 87.5 % and 96.2 %, respectively, whereas the one-step revealed 84.6 % and 96.2 %, respectively.

One-step 3^rd-generation RIA may be used for the reliable detection of TRAb. The shorter and easier assay design may improve its use and enable automation in routine nuclear medicine laboratories.