title: Tissue Xpert™ MTB/Rif assay is of limited use in diagnosing peritoneal tuberculosis in patients with exudative ascites.
abstract: BACKGROUND
  Xpert™ MTB/Rif is a multiplex hemi-nested real-time PCR-based assay to detect presence of M. tuberculosis within 2 hours of sample collection. The present study aimed at assessing efficacy of Xpert™ MTB/Rif assay for diagnosing peritoneal tuberculosis.
  
  
  METHODS
  Patients with exudative ascites, fluid negative for acid-fast bacilli on auramine O fluorescence staining and unyielding fluid cytology for malignant cells, were included. Ultrasound-guided omental biopsy samples were obtained in all. Xpert™ MTB/Rif assay on tissue samples was assessed against a composite "reference" standard for diagnosis of peritoneal tuberculosis, defined as presence of any of the three-culture showing M tuberculosis, granulomatous inflammation on histology or resolution of ascites with 2 months of antitubercular therapy.
  
  
  RESULTS
  During January 2012-July 2013, 28 patients (age:43 ± 15 years; mean ± SD; male:20) were recruited. Serum ascitic albumin gradient was <1.1 in all except in four patients with underlying cirrhosis. Twenty-one of the 28 patients had peritoneal TB as diagnosed by composite reference standard (histology:18; culture:4; treatment response:3). Seven patients (25%) had an alternative diagnosis (metastatic carcinoma 2, adenocarcinoma 2, mesothelioma 2, and systemic lupus erythematous 1). Xpert™ MTB/Rif assay was positive in 4/21 patients with peritoneal tuberculosis and in none of the 7 patients with alternative diagnosis. Thus, sensitivity, specificity, positive, and negative predictive values for tissue Xpert™ MTB/Rif assay in diagnosing peritoneal tuberculosis were 19% (95% C.I: 6% to 42%), 100% (95% C.I: 59% to 100%), 100% (40% to 100%), and 29% (95% C.I: 13% to 51%), respectively.
  
  
  CONCLUSIONS
  Tissue Xpert™ MTB/Rif assay was of limited use in diagnosing peritoneal tuberculosis.
authors.affiliation: Department of Hepatology, Christian Medical College, Vellore, 632 004, India.
authors.forename: Chinmay
authors.initials: C
authors.lastname: Bera
authors.affiliation: Department of Microbiology, Christian Medical College, Vellore, 632 004, India.
authors.forename: Joy Sarojini
authors.initials: JS
authors.lastname: Michael
authors.affiliation: Department of Pathology, Christian Medical College, Vellore, 632 004, India.
authors.forename: Deepak
authors.initials: D
authors.lastname: Burad
authors.affiliation: Department of Microbiology, Christian Medical College, Vellore, 632 004, India.
authors.forename: Suzana B
authors.initials: SB
authors.lastname: Shirly
authors.affiliation: Department of Radiology, Christian Medical College, Vellore, 632 004, India.
authors.forename: Sridhar
authors.initials: S
authors.lastname: Gibikote
authors.affiliation: Department of Pathology, Christian Medical College, Vellore, 632 004, India.
authors.forename: Banumathi
authors.initials: B
authors.lastname: Ramakrishna
authors.affiliation: Department of Hepatology, Christian Medical College, Vellore, 632 004, India. drashishgoel@cmcvellore.ac.in.
authors.forename: Ashish
authors.initials: A
authors.lastname: Goel
authors.affiliation: Department of Hepatology, Christian Medical College, Vellore, 632 004, India.
authors.forename: C E
authors.initials: CE
authors.lastname: Eapen
mesh_terms: D000328:Adult; D001201:Ascites / Q000382:microbiology*; D005122:Exudates and Transudates / Q000382:microbiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000302:isolation & purification; D009852:Omentum / Q000382:microbiology; D014395:Peritonitis, Tuberculous / Q000175:diagnosis* / Q000382:microbiology*; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D013997:Time Factors
keywords: Granuloma; M. tuberculosis; Omental biopsy; Xpert™ MTB/Rif assay