Rapid diagnosis of pleural tuberculosis by Xpert MTB/RIF assay using pleural biopsy and pleural fluid specimens

BACKGROUND Early pleural tuberculosis (TB) diagnosis is particularly difficult. The aim of this study was to investigate the diagnostic accuracy of the Xpert MTB/RIF (Xpert) (Cepheid, Sunnyvale, CA) assay using pleural biopsy and pleural fluid specimens in patients with suspected pleural TB but who had a negative sputum acid-fast bacilli (AFB) smear. MATERIALS AND METHODS In this study, 134 sputum smear-negative suspected pleural TB patients were selected. Paired pleural fluid and pleural biopsy specimens were tested for Mycobacterium tuberculosis by standard smear-microscopy, Lowenstein-Jensen and mycobacterial growth indicator tube (MGIT) culture, and the Xpert assay. Mycobacterial culture from pleural biopsy specimens was used as a reference standard for sensitivity and specificity calculations. Detection of rifampicin resistance was compared with the MGIT method. RESULTS Of 126 evaluable patients, 55 received a diagnosis of pleural TB. The sensitivity of the Xpert assay using pleural biopsy specimens for the diagnosis of pleural TB was 85.5%, and specificity was 97.2%. The sensitivity and specificity of the Xpert assay in pleural fluid were 43.6% and 98.6%, respectively. The Xpert assay correctly identified 90.0% of phenotypic rifampicin-resistant cases and 93.9% of phenotypic rifampicin-susceptible cases. CONCLUSION The Xpert assay on pleural biopsy specimens may provide an accurate diagnosis of pleural TB in patients who had a negative AFB smear.