Abstract
Aim: The diagnostic accuracy of interferongamma- based assays for Mycobacterium tuberculosis infection may be improved by using lower cut-off values for the tuberculin skin testing (TST), QuantiFERON-TB Gold (QFT) and Interferon gamma inducible protein (IP)-10.
Methods: A total of 70 adult TB patients and 81 healthy controls were included for this study.Three assays, TST, QFT and (IP)-10, were evaluated for their diagnostic performance with respect to different cut-off values. Test cut-offs were established based on receiver operating characteristic curve analysis.
Results: The sensitivities of the assays were: TST 40 %, QFT 87 % and IP-10 85 %, while their specificities were TST 58 %, QFT 71 % and IP-10 74 %. Both QFT and IP-10 were significantly more specific than TST (both P< 0.001), but were similiar to each other (P > 0.5). Receiver operating characteristic analysis revealed that a cut-off value of 0.29 IU/ml for QFT and 1857 IU/ml for IP-10 maximises specificity without significant loss of test sensitivity. Using lower cut-off values for TST, however, also increased the sensitivity of the assay but resulted in a significant decrease in specificity.
Conclusions: Lower cut-off values for TST, QFT and (IP)-10 increased the sensitivity of each assay, but a lower cut-off value for QFT and (IP)-10 could specificity be maintained.
- © 2012 ERS