Intest Res  
Evaluation of Xpert MTB/RIF assay performance in the diagnosis of abdominal tuberculosis
Suraj Kumar1, Sawan Bopanna1, Saurabh Kedia1, Pratap Mouli1, Rajan Dhingra1, Rajesh Padhan1, Mikashmi Kohli2, Jigyasa Chaubey2, Rohini Sharma2, Prasenjit Das3, S Dattagupta3, Govind Makharia1, SK Sharma2, Vineet Ahuja1
Departments of 1Gastroenterology, 2Medicine, and 3Pathology, All India Institute of Medical Sciences, New Delhi, India
Correspondence to: Vineet Ahuja, Department of Gastroenterology, All India Institute of Medical Sciences, Room No. 3093, 3rd Floor, Teaching Block, New Delhi 110029, India. Tel: +91-11-26593300, Fax: +91-11-2658663, E-mail: vineet.aiims@gmail.com
Received: May 11, 2016; Revised: July 21, 2016; Accepted: July 21, 2016; Published online: March 20, 2017.
© Korean Association for the Study of Intestinal Diseases. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background/Aims: The use of genetic probes for the diagnosis of pulmonary tuberculosis (TB) has been well described. However, the role of these assays in the diagnosis of intestinal tuberculosis is unclear. We therefore assessed the diagnostic utility of the Xpert Mycobacterium tuberculosis /rifampicin (MTB/RIF) assay, and estimated the prevalence of multidrug-resistant (MDR) TB in the Indian population . Methods: Of 99 patients recruited, 37 had intestinal TB; two control groups comprised 43 with Crohn’s disease (CD) and 19 with irritable bowel syndrome. Colonoscopy was performed before starting any therapy; mucosal biopsies were subjected to histopathology, acid-fast bacilli staining, Lowenstein-Jensen culture, and nucleic acid amplification testing using the Xpert MTB/RIF assay. Patients were followed up for 6 months to confirm the diagnosis and response to therapy. A composite reference standard was used for diagnosis of TB and assessment of the diagnostic utility of the Xpert MTB/RIF assay. Results: Of 37 intestinal TB patients, the Xpert MTB/RIF assay was positive in three of 37 (8.1%), but none had MDR-TB. The sensitivity, specificity, positive predictive value, and negative predictive value of the Xpert MTB/RIF assay was 8.1%, 100%, 100%, and, 64.2%, respectively. Conclusions: The Xpert MTB/RIF assay has low sensitivity but high specificity for intestinal TB, and may be helpful in endemic tuberculosis areas, when clinicians are faced with difficulty differentiating TB and CD. Based on the Xpert MTB/RIF assay, the prevalence of intestinal MDR-TB is low in the Indian population.
Keywords: Tuberculosis, multidrug-resistant; Crohn disease; Xpert MTB/RIF assay


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