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

Aim 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. Methods 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). Results 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. Conclusion 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.