A retrospective study on Xpert MTB/RIF for detection of tuberculosis in a teaching hospital in China

The Xpert MTB/RIF assay is an automated molecular test that is designed to simultaneously detect Mycobacterium tuberculosis (MTB) complex and rifampin resistance. However, there are relatively few studies on this method in China. Xpert has been routinely used at Peking University People's Hospital (PKUPH) since November 2016. Thus, the aim of this study was to evaluate the performance of Xpert, and provide a reference and guidance for the detection and diagnosis of TB in non-TB specialized hospitals.

The medical records of inpatients simultaneously tested with Xpert, acid-fast bacilli (AFB) smear microscopy, and interferon-gamma release assay (IGRA, by T-SPOT®.TB) at PKUPH from November 2016 to October 2018 were reviewed. Active TB cases were considered according to a composite reference standard (CRS). Then, the three methods were evaluated and compared.

In total, 787 patients simultaneously tested with Xpert, AFB, and IGRA were enrolled; among them 11.3% (89/787) were diagnosed and confirmed active pulmonary TB (PTB, 52 cases), extrapulmonary TB (EPTB, 17 cases), and tuberculous pleurisy (TP, 20 cases). The sensitivity of Xpert in detecting PTB, EPTB, and TP was 88.5, 76.5, and 15.0%, respectively, which was slightly lower than IGRA (96.2, 82.4, and 95.0%, respectively), but higher than AFB (36.5, 11.8, and 0%, respectively); IGRA showed the highest sensitivity, but its specificity (55.9, 67.1, and 45.2%, respectively) was significantly lower than Xpert (99.6, 99.4, and 100%, respectively) and AFB (99.0, 99.4, and 100%, respectively) (P < 0.001). The sensitivity of Xpert in detecting lung tissue, cerebrospinal fluid, lymph nodes, and joint fluid was 100%, followed by sputum (88.5%), alveolar lavage (85.7%), and bronchoscopy secretion (81.2%); the pleural fluid sensitivity was the lowest, only 15.0%. For AFB negative patients, the sensitivity of Xpert in detecting PTB, EPTB, and TP was 84.9, 73.3, and 15.0%, respectively.

Xpert showed both high sensitivity and high specificity, and suggested its high value in TB diagnosis; however, the application of pleural fluid is still limited, and should be improved. Owing to the high sensitivity of IGRA, it is recommended for use as a supplementary test, especially for assisting in the diagnosis of TP and EPTB.