We evaluated the technical robustness of the new commercial TBII assay using human
recombinant TSH-R, and describe its use for the clinician in the routine laboratory.
The human recombinant TSH-R assay (DYNOtest® TRAK human) was compared to a conventional
TBII assay (TSH-REZAK®). Specificity was adjusted at 99.1% for both assays by ROC
plot analysis including 113 healthy individuals. Sensitivity in 115 patients with
active Graves' Disease (GD) was 98.2% for the DYNOtest® TRAK human compared to 68.4%
for the TSH-REZAK® (p < 0.0001). Comparison of the ROC-calculated cut off confirmed the recommended cut-off
for the DYNOtest®TRAK human, since 11% inhibition of tracer equals 1 IU/L, which is
recommended as the grey zone. At the recommended cut-off (2 IU/I, 22% inhibition),
the sensitivity is still 93.9% with 100% specificity. The ROC plot-derived cut-off
of the TSH-REZAK® (4.4%, 2 to 10 U/L) is below the grey zone of 10-15 U/L. At the
recommended cut off of 15 U/L, the sensitivity is 43.0% with a specificity of 100%.
Both assays showed a good correlation (r = 0.82, p < 0.0001); however, assay comparison revealed a constant bias in favour of the DyNOtest®
TRAK human. Applying the ROC plot-derived cut-off of 11% inhibition (1 IU/L) for the
DYNOtest® TRAK human, we found 15 of 50 patients with autoimmune thyroiditis (AIT)
and 6 of 23 patients with goitre (all < 1.5 IU/L). These patients would have been
missed using the recommended 2 IU/L. The difference in sensitivity between the DYNOtest®
TRAK human and the TSH-REZAK® was highly significant in the GD group, but not in other
groups, indicating that the DYNOtest® TRAK human has a higher sensitivity for GD without
compromising specificity. In summary, the proposed high sensitivity of the new TBII
assay using human recombinant TSH-R could be confirmed with the commercial product.
This method offers a clear advantage over conventional TBII assays to confirm or exclude
the diagnosis of GD. The recommended cut-off is very stringent, and until we have
more information on the clinical relevance of low-level TBII between 1 and 1.5 IU/L,
those patients should be monitored for the development of autoimmune thyroid disease.
Key words
Graves' Disease - Antibodies - TSH Receptor
