Setting: Nucleic acid amplification tests can detect Mycobacterium tuberculosis complex rapidly and reliably.
Objective: To compare the diagnostic performance of the artus M. tuberculosis PCR Kit and COBAS AMPLICOR Mycobacterium tuberculosis Test. In the artus assay, an appropriate cycle threshold (Ct) value was determined for positivity.
Design: A total of 238 clinical respiratory specimens were analysed using both the artus and COBAS AMPLICOR assays. In 221 specimens, these results were further compared with culture results.
Results: The overall agreement between artus and COBAS AMPLICOR was 96.2% (229/238). Among the nine (3.8%) discrepant specimens, three (1.3%) were artus-positive and COBAS AMPLICOR-negative, while the other six (2.5%) were artus-negative and COBAS AMPLICOR-positive. Using culture as a standard, the sensitivity and specificity of the artus assay were 97.8% and 85.1%, and those of COBAS AMPLICOR assay were 100% and 86.2%, respectively. The difference was not statistically significant. In the artus assay, the minimum Ct value for the positivity determination was 38.
Conclusion: The artus and COBAS AMPLICOR assays showed comparable diagnostic performance and can be confidently used for detection of M. tuberculosis complex. In the artus assay, a Ct value of 38 could be suggested as an appropriate cut-off value.