Abstract
Until recently, stimulating TSH receptor autoantibodies (sTRAbs) could only be measured
by bioassays. A new assay system, which directly detects sTRAb in sera by applying
bridge technology, has been established and is now available as automated chemiluminescence
(bridge) immunoassay. We evaluated the automated bridge assay in clinical routine
and compared it with a conventional automated TRAb assay (competition assay). Altogether,
226 Graves’ disease (GD), 57 autoimmune thyroiditis, 74 non-autoimmune nodular goiter
and 49 thyroid cancer patients, as well as 41 healthy controls were retrospectively
evaluated. ROC plot analysis based on sera of newly diagnosed GD patients revealed
an area under curve of 0.99 (95% CI: 0.99–1.0) indicating a high assay sensitivity
and specificity. The highest sensitivity (100%) and specificity (99%) were seen at
a cut-off level of 0.55 IU/l. The calculated positive predictive value was 94%, whereas
the negative was 100%. Applying a ROC plot-derived cut-off of≥0.30 IU/l, derived from
sera of GD patients already receiving antithyroid drug therapy for≤6 months, the sensitivity
was 99% whereas the specificity was 98%. Detailed comparison of both assay systems
used revealed a slightly different distribution of sTRAb and TRAb. Measurement of
sTRAb during follow-up revealed a steady decline over one year of follow-up. In summary,
our results demonstrate that the new automated bridge assay system for detecting sTRAb
has a high sensitivity and specificity for diagnosing GD and to discriminate from
other thyroid diseases, respectively. Our study, however, does not provide full evidence
that the bridge assay is specific for sTRAb only.
Key words
Graves’ disease - autoimmune thyroiditis - bridge assay
