Performance of Xpert MTB/RIF Assay in Diagnosis of Pleural Tuberculosis by Use of Pleural Fluid Samples

Abstract

Prospectively, 162 pleural fluid samples from patients with probable tuberculous pleural effusion were tested by the Xpert MTB/ RIF assay and the Bactec MGIT-960 culture system. Of these, 43 (26.5%) were positive in the MGIT-960 culture, and 23 (14.2%), in the Xpert MTB/RIF assay. The sensitivity and specificity of the Xpert MTB/RIF compared with the MGIT-960 culture were 54.8% and 100%, respectively. T uberculosis (TB) affects one third of the global population in developing countries, with annual estimates of 9.0 million new cases and 1.5 million deaths (1). While pulmonary tuberculosis (PTB) is the most common presentation, extrapulmonary tuberculosis (EPTB) is also an important clinical condition (2). Pleural TB occurs in up to 30% of patients concomitantly with pulmonary TB and contributes a major portion of extrapulmonary TB (3). The disease remains undiagnosed in the majority of cases due to its paucibacillary nature. The conventional methods of culture on solid and liquid media are gold standard for diagnosis, but the longer turnaround time (TAT) added with the relatively high cost for infrastructure development remain problems in resource-limited settings (4). Interferon gamma (IFN-␥) assay has also been reported as an alternative biological marker for pleural TB diagnosis by some workers (5).The Xpert MTB/RIF assay (Cepheid, Inc., Sunnyvale, CA, USA) is a rapid, automated molecular test with good sensitivity for pulmonary TB. However, on its utility in pleural TB, only a few studies with small sample size have been carried out; most of these were from low-TB-burden countries (6-8), and none were from India.This prospective observational study was conducted at the Government of India-approved culture & drug susceptibility testing (C&DST) laboratory, Division of Clinical Microbiology and Molecular Medicine, All India Institute of Medical Sciences, New Delhi. A total of 162 pleural fluid samples were obtained from patients having high suspicions of pleural TB. Eligibility for enrollment was based on standard clinical and radiological criteria, including a persistent cough of 2 weeks or more, unexplained fever for 2 weeks or more, unexplained weight loss with or without night sweats, chest pain, and radiological evidence of pleural effusion. Thus, no separate ethical clearance was required for this study. Patients who were receiving treatment at the time of enrollment were excluded from the study. All patients included were HIV negative.One aliquot of the sample was used for the MGIT-960 culture, and the other, for the Xpert MTB/RIF assay. The Xpert MTB/RIF assay was performed directly on pleural fluid samples according to the manufacturer's instruction, using the newer version (G4) of cartridges and the newer software version 4.4a, as published earlier (9). Briefly, 1 ml of uncentrifuged pleural fluid sample was lysed with 3 ml of sample reagent (SR) buffer (3:1) and incubated for 15 min at room temperature; finally, 2 ml of mixture was loaded in cartridge. The instrument after DNA amplification detects t...

Evaluation of GeneXpert MTB/RIF assay in diagnosis of extrapulmonary tuberculosis and rifampicin resistance

“…There was no rifampicin resistance in the population studied, all the 23 MTB positive samples detected by Gene Xpert-MTB/RIF assay in our study were sensitive to Rifampicin. This finding was in accordance with Rufai et al [14], who have also reported similar sensitivity of rifampicin, whereas Pravin et al [11] detected Rifampicin resistance in 4 out of 16 MTB detected in the pleural fluid and one rifampicin resistance out of 5 MTB detected in the ascitic fluid samples.…”

“…In a study conducted by Praveen et al [11], they found 10.1% plueral fluid sample positive for MTB by Gene Xpert and Hillemann et al [13] found 3 positive GeneXpert results out of 113 pleural fluid samples (2.9%) all of which were negative on mycobacterial culture, the positivity rate for pleural fluids in our study was 6.06% (8/132) was in accordance with above studies. Rufai et al [14] showed that the Xpert has very low diagnostic sensitivity of 14.2% in pleural fluid, even in culture proven cases. Porcel et al [15] concluded that the Xpert MTB/RIF assay has a limited diagnostic capacity for pleural fluid samples of TB origin.…”

A diagnostic algorithm for tuberculous pleurisy using the ELISPOT assay on peripheral blood and pleural effusion

“…[30] However, its sensitivity for diagnosing TB pleurisy is disappointingly low. [31][32][33][34] Recently, a meta-analysis reported the pooled sensitivity and specificity of Xpert MTB/RIF to be 37% and 92%, respectively, in TB pleurisy. [35] The paucibacillary nature of pleural specimens was considered to be the main reason for this.…”

Rapid Detection of Cell-Free Mycobacterium tuberculosis DNA in Tuberculous Pleural Effusion

“…The definite diagnosis of TP is made by detecting Mycobacterium tuberculosis from the pleural effusion (PE), sputum, or pleural tissue (1,2). However, due to the paucity of M. tuberculosis organisms in PE, culture and molecular tests like the Xpert MTB/RIF assay show poor sensitivities (3)(4)(5).…”