Performance of Xpert MTB/RIF on pleural tissue for the diagnosis of pleural tuberculosis

Abstract

Tuberculosis (TB) remains the second leading cause of death from an infectious disease in adults. Extrapulmonary TB (EPTB) accounts for about 25% of all cases of active TB. Pleural TB is the second most common manifestation of EPTB.Existing tests for the diagnosis of pleural TB have major limitations in terms of accuracy, time to diagnosis and drug resistance testing, and require special expertise for sample acquisition and interpretation of the results. Biopsy of the pleural tissue for combined histological examination and culture is considered the diagnostic gold standard, albeit imperfect [1,2].The Xpert MTB/RIF assay (Xpert; Cepheid, Sunnyvale, CA, USA) is a rapid, World Health Organization (WHO) endorsed, automated PCR test optimised for respiratory specimens that can detect both Mycobacterium tuberculosis (MTB) and rifampicin resistance [3,4]. Given the limitations of available tests for the diagnosis of pleural TB, several studies have evaluated the performance of Xpert using pleural fluid as a sample type. Overall, these studies show limited accuracy with sensitivity averaging around 44% [5][6][7]. However, the preferred specimen for the diagnosis of pleural TB is pleural tissue. To date, the evaluation of Xpert performed on pleural tissue has been limited to isolated samples within larger studies [4,6,7].We enrolled consecutive adult patients that were evaluated for pleural TB in the pulmonary clinic and inpatient ward at the Christian Medical College, Vellore, India. Pleural TB was suspected based on clinical symptoms and radiographic evidence of a pleural effusion. Information on demographics, comorbidities, presenting symptoms and results of diagnostic evaluation were collected prospectively. The institutional review boards of the Christian Medical College and McGill University, Montreal, Canada, approved the study.All recruited patients underwent thoracentesis for evaluation of pleural fluid. One specimen was processed with routine diagnostics including fluorescence smear microscopy, adenosine deaminase (ADA; Diazyme Laboratories, San Diego, CA, USA), liquid cultures (Mycobacterium Growth Indicator Tube; Becton Dickinson, Sparks, MD, USA) and solid cultures (Löwenstein-Jensen medium). The second sample was used for Xpert testing. A pleural biopsy was performed, when clinically indicated and safely feasible. Pleural tissue was evaluated with histopathology, smear microscopy and culture. : sensitivity 0% (none out of 17; 95% CI 0-20%) and specificity 97.4% (37 out of 38; 95% CI 86-100%). 1427Pleural fluid was centrifuged (1370 6g for 15 min) and the concentrated sediment, resuspended in 1 mL of the original supernatant, was used for Xpert [5]. Pleural tissue was finely ground and re-suspended in 1 mL of sterile saline [8]. The Xpert ''sample reagent'' was added (2:1 ratio for both pleural fluid and pleural tissue samples) and, after incubation, 2 mL were transferred into a G4 cartridge.We defined two composite reference standards (CRS) for the diagnosis of TB. The first CRS (CRS-1) identified confirme...

Evaluation of Xpert MTB/RIF assay performance in diagnosing extrapulmonary tuberculosis among adults in a tertiary care centre in India

“…Suboptimal performance of the assay was observed for various body fluids, with sensitivity ranging from 18% to 40%, which is consistent with several previous studies [7][8][9][10][11][12]. The present study also indicates exemplary performance of the assay in patients with cold abscesses and lymph nodes and these findings are similar to previously published literature [7][8][9]13].…”

“…In the present study, we excluded patients who were already on anti-TB treatment for .2 weeks. The overall performance of Xpert MTB/RIF in our study might vary from different studies across the globe because of the variation in proportion of sample types [7][8][9][10][11][12][13][14][15].…”

Xpert MTB/RIF assay for the diagnosis of extrapulmonary tuberculosis: a systematic review and meta-analysis

“…1) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] that included 4461 samples. TB prevalence (based on culture) ranged from 0% to 81%.…”

“…Only four (25%) studies used the protocol (i.e. volume of sample included and sample reagent to sample ratio) recommended by the manufacturer [36] for unprocessed sputum samples [17,19,29,25] (table 2). Most of the studies that included a mechanical homogenisation step (40%) also performed a decontamination procedure with N-acetyl-L-cysteine and sodium hydroxide solution.…”

“…Seven studies included only one sample type (e.g. pleural fluid only) [17,18,21,25,26,30,39] (table 1). The remainder of the studies included different sample types in varying percentages.…”