Abstract
A rapid and fully automated chemiluminescent immunoassay for the detection of thyrotropin
receptor autoantibodies (TSHR-Ab) based on a bridge technology was compared with two
bioassays that measure either stimulating (TSAb) or blocking (TBAb) antibodies for
the detection and differentiation of TSHR-Ab. A total of 229 patients with various
thyroid disorders [151 with Graves’ disease (GD), 35 with Hashimoto’s thyroiditis
(HT), 32 with nodular goiter, and 11 with thyroid cancer] were included. The bridge
immunoassay was performed according to the manufacturer’s instructions (cut-off>0.55 IU/l).
TSAb and TBAb were measured with reporter bioassays. Blocking activity was defined
as percent inhibition of luciferase expression relative to induction with bovine TSH
alone (cut-off>34% inhibition). TSAb was reported as percentage of specimen-to-reference
ratio (> 140 SRR%). The 3 TSHR-Ab assays were negative in all patients with benign
euthyroid nodular goiter and differentiated thyroid cancer. In contrast, in all patients
with GD, irrespective of the disease duration, TSHR-Ab positivity was present in 127
of 151 (84%) and 140 (93%) for the bridge assay and TSAb bioassay, respectively (p<0.001).
Fifteen of 151 (10%) GD samples were positive in the TSAb bioassay but negative in
the bridge assay. The bridge assay and the TSAb bioassay correlated positively (r=0.39,
p<0.0001) in patients with GD. Both assays detected TSHR-Ab in all ten untreated hyperthyroid
patients with GD. In GD patients with a duration of less than six months, 27/29 (93%)
and 28 (97%) were TSHR-Ab positive with the bridge and TSAb bioassay, respectively.
In comparison, TSHR-Ab were present in two of 35 (6%) and five (14%) HT patients with
the bridge and TSAb bio-assay, respectively. TSHR blocking antibodies were present
in one (3%) patient with HT and in two (1%) patients with GD; these two GD patients
were also bridge assay positive but TSAb bioassay negative. In conclusion, the bridge
immunoassay and both bioassays are highly sensitive for the detection of TSHR-Ab.
The bridge assay is, however, also positive in the presence of TSHR blocking antibodies
detected in a TBAb bioassay.
Key words
TSH receptor functional antibodies - bridge immunoassay - cell-based bioassay
