Rapid diagnosis of extrapulmonary tuberculosis with Xpert Mycobacterium tuberculosis/rifampicin assay

Abstract

Purpose: XpertMycobacterium tuberculosis/rifampicin (Xpert MTB/RIF) assay has been endorsed by the World Health Organization (WHO) for diagnosis of extrapulmonary tuberculosis (EPTB), while the sensitivity and specificity have not been fully evaluated. We aimed to evaluate the performance of Xpert MTB/RIF assay in the detection of different extrapulmonary specimens.

Methods: A total of 420 nonrespiratory specimens were detected with acid-fast bacilli (AFB) smear microscopy, solid culture, conventional drug susceptibility testing (DST) and Xpert MTB/RIF assay. Using solid culture and conventional DST as the gold standard, we assessed the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of the Xpert MTB/RIF assay for detecting MTB and rifampin resistance, respectively.

Results: When setting the solid culture results as the gold standard, the sensitivity, specificity, PPV, NPV and Kappa value of Xpert MTB/RIF assay and AFB smear results were 70.6 % (48/68), 91.96 % (318/346), 63.2 % (48/76), 94.1 % (318/338), 0.60, respectively. In addition, when compared with conventional DST results, the sensitivity, specificity, PPV, NPV and Kappa of the Xpert MTB/RIF assay for detecting rifampin resistance were 91.7 % (11/12), 100.0 % (47/47), 100.0 % (11/11), 97.9 % (47/48) and 0.95, respectively.

Conclusion: Compared with AFB smear and solid culture, Xpert MTB/RIF assay has high sensitivities and short detection time, so could be used as an alternative for the rapid diagnosis of EPTB and rifampin resistance in clinical practice.