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. 2015 Sep;34(5):395-8.
doi: 10.1007/s12664-015-0599-7. Epub 2015 Nov 4.

Tissue Xpert™ MTB/Rif assay is of limited use in diagnosing peritoneal tuberculosis in patients with exudative ascites

Chinmay Bera  1 , Joy Sarojini Michael  2 , Deepak Burad  3 , Suzana B Shirly  2 , Sridhar Gibikote  4 , Banumathi Ramakrishna  3 , Ashish Goel  5 , C E Eapen  1
Affiliations

Tissue Xpert™ MTB/Rif assay is of limited use in diagnosing peritoneal tuberculosis in patients with exudative ascites

Chinmay Bera et al. Indian J Gastroenterol. 2015 Sep.

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.

Interpretation and conclusion: Tissue Xpert™ MTB/Rif assay was of limited use in diagnosing peritoneal tuberculosis.

Keywords: Granuloma; M. tuberculosis; Omental biopsy; Xpert™ MTB/Rif assay.

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