title: Performance of Xpert MTB/RIF on Ascitic Fluid Samples for Detection of Abdominal Tuberculosis.
abstract: BACKGROUND
  Diagnosis of abdominal tuberculosis (TB) from ascitic fluid samples using routinely available diagnostic methods is challenging due to its paucibacillary nature. Although performance of Xpert MTB/RIF assay has been evaluated extensively on pulmonary samples, its performance on extrapulmonary samples is still under evaluation.
  
  
  OBJECTIVE
  The objective of this study was to find out the performance of Xpert MTB/RIF on ascitic fluid samples obtained from suspected cases of abdominal TB. Performance was compared withMycobacteriumgrowth indicator tube-960 (MGIT-960) culture and in-house multiplex polymerase chain reaction (PCR). The latter detects and differentiatesMycobacterium tuberculosisand nontuberculous mycobacteria simultaneously.
  
  
  METHODS
  Sixty-seven patients suspected of probable/possible abdominal TB were included in this observational, prospective study. All samples were tested by Ziehl-Neelsen staining, MGIT-960 culture, in-house multiplex PCR, and Xpert MTB/RIF assay.
  
  
  RESULTS
  All 67 samples were smear negative. Seventeen (25.4%) were MGIT-960 culture positive while 12 (17.9%) were detected positive by the Xpert MTB/RIF assay and 9 (13.4%) by in-house multiplex PCR. Sensitivity and specificity of the Xpert MTB/RIF assay compared with the MGIT-960 culture were 70.6% (95%, confidence interval [CI]: 44.1-89.7) and 100% (95%, CI: 92.8-100) and that of in-house multiplex PCR were 52.9% (95%, CI: 30.9-73.8) and 100% (95%, CI: 92.8-100), respectively.
  
  
  CONCLUSIONS
  Diagnostic yield of Xpert MTB/RIF assay on ascitic fluid samples was lower than MGIT-960 culture. We thus emphasize on the need for urgent discovery of new biomarkers for paucibacillary TB.
authors.affiliation: Division of Clinical Microbiology and Molecular Medicine, Department of Laboratory Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Syed Beenish
authors.initials: SB
authors.lastname: Rufai
authors.affiliation: Division of Clinical Microbiology and Molecular Medicine, Department of Laboratory Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Sarman
authors.initials: S
authors.lastname: Singh
authors.affiliation: Division of Clinical Microbiology and Molecular Medicine, Department of Laboratory Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Amit
authors.initials: A
authors.lastname: Singh
authors.affiliation: Division of Clinical Microbiology and Molecular Medicine, Department of Laboratory Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Parveen
authors.initials: P
authors.lastname: Kumar
authors.affiliation: Division of Clinical Microbiology and Molecular Medicine, Department of Laboratory Medicine, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: Jitendra
authors.initials: J
authors.lastname: Singh
authors.affiliation: Department of Medicine, Dr. Ram Manohar Lohia Hospital, PGIMER, New Delhi, India.
authors.forename: Anand
authors.initials: A
authors.lastname: Vishal
keywords: Abdominal tuberculosis; Mycobacterium growth indicator tube-960 culture; Xpert MTB/RIF; ascitic fluid; multiplex polymerase chain reaction