Comparative Diagnostic Performance of Three Commercial Real-Time PCR Assays for the Detection of Mycobacterium tuberculosis Complex in Bronchial Washing Specimens: A Large Retrospective Study.

Abstract

Background: Molecular assays are essential for the rapid detection of Mycobacterium tuberculosis complex (MTBC). However, head-to-head comparisons of widely used commercial assays remain limited. This study compared the diagnostic performance of three real-time PCR assays-AdvanSure TB/NTM, Cobas MTB, and Xpert MTB/RIF-using bronchial washing specimens.

Methods: We retrospectively analyzed molecular assay results from 3348 bronchial washing specimens obtained between January 2021 and May 2024. Among them, 740 specimens were included in a head-to-head comparison of the three assays. Diagnostic performance was evaluated using culture-confirmed MTBC as the reference standard.

Results: In the head-to-head comparison (n = 740), the overall concordance rate was 93.6%. Using culture-confirmed MTBC as the reference standard, the sensitivities of the AdvanSure, Cobas, and Xpert assays were 49.1%, 96.2%, and 90.6%, respectively. In smear-negative cases (n = 713), AdvanSure showed markedly lower sensitivity (30.8%) than the Cobas (94.9%) and Xpert (87.2%). AdvanSure showed the highest overall specificity (98.7%), followed by Cobas (96.9%) and Xpert (96.4%). The Xpert MTB/RIF assay demonstrated complete concordance with drug susceptibility testing for detecting rifampicin resistance, with a sensitivity of 100% (95% CI, 59.0%-100.0%) and a specificity of 100% (95% CI, 97.3%-100.0%).

Conclusion: In this real-world cohort with a high proportion of smear-negative cases, the Cobas and Xpert assays exhibited significantly higher sensitivity for MTBC detection than the AdvanSure assay. These findings highlight the importance of highly sensitive molecular assays for the early diagnosis of pulmonary tuberculosis, particularly in patients with low bacillary burden.