Efficacy of the Xpert Mycobacterium tuberculosis/rifampicin assay for diagnosing sputum-smear negative or sputum-scarce pulmonary tuberculosis in bronchoalveolar lavage fluid

Objective: To evaluate he diagnostic performance of the Xpert Mycobacterium tuberculosis/Rifampin (MTB/RIF) assay in bronchoalveolar lavage fluid (BALF). Methods: We retrospectively reviewed the clinical data from 671 sputum-smear negative or sputum scarce adult patients with suspected pulmonary tuberculosis (PTB) who had an Xpert MTB/RIF assay performed on BALF. The diagnostic performance of the Xpert MTB/RIF assay, smear microscopy (SM) and MTB culture was evaluated using MTB culture or final clinical diagnosis as the reference standard. Results: Compared with MTB culture, the sensitivity and specificity were 87.8% and 72.7% for the Xpert MTB/RIF assay and 11.0% and 99.2% for SM, respectively. Compared with final diagnosis, diagnostic performance was 58.9% and 83.9% for the Xpert MTB/RIF assay, 5.0% and 98.3% for SM, and 43.3% and 100% for culture, for sensitivity and specificity respectively. The Xpert MTB/RIF assay had low specificity and high sensitivity. When very low results were re-evaluated and considered MTB-negative, the specificity increased significantly. The sensitivity remained higher than SM and was similar to that of culture. Conclusions: The Xpert MTB/RIF assay adds microbiologic evidence to clinical decisions; however, close attention should be paid to very low semi-quantitative positive results. (c) 2021 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).

Automated summary

The Xpert MTB/RIF assay demonstrated high sensitivity and moderate specificity in diagnosing pulmonary tuberculosis in bronchoalveolar lavage fluid (BALF), providing valuable microbiological evidence for clinical decisions. Special attention should be paid to re-evaluating very low semi-quantitative positive results to improve specificity.