Evaluation of Xpert MTB/RIF assay performance in the diagnosis of abdominal tuberculosis

Abstract

Background/AimsThe 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.MethodsOf 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.ResultsOf 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.ConclusionsThe 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.

Multiplex Polymerase Chain Reaction for diagnosis of gastrointestinal tuberculosis

“…However, the yield of culture and histopathology is generally quite low in GITB, which is generally a paucibacillary disease. Response to empirical antitubercular therapy or a therapeutic trial has also been considered as an important diagnostic tool in studies . To deal with these problems and to compare recent upcoming molecular methods, recent studies have used a composite diagnostic standard for the evaluation of new diagnostic tests .…”

“…16 To deal with these problems and to compare recent upcoming molecular methods, recent studies have used a composite diagnostic standard for the evaluation of new diagnostic tests. 16 We used similar criteria for the diagnosis of GITB. A confirmed diagnosis of GITB was made if any one of the following four criteria were met, that is, (i) histopathology of intestinal tissue showed caseating granulomas, granulomas with acid-fast bacilli; (ii) granulomatous inflammation without caseation or acid-fast bacilli (AFB) but good clinical response to antitubercular therapy (ATT); (iii) isolation of AFB bacilli in samples obtained from extraintestinal sites like sputum, resected tissues, lymph nodes, etc.…”

Making a Positive Diagnosis of Intestinal Tuberculosis with the Aid of New Biologic and Histologic Features: How Far Have We Reached?

“…Among the latter, the sensitivity of the Gene Xpert assay was 88% and its specificity was 91%. Kumar et al [36] found that the sensitivity, the specificity, the positive predictive value, and the negative predictive value of the Gene Xpert assay were 8.1, 100, 100, and 64.2%, respectively, in intestinal TB cases.…”

Recent advancements in management of gastrointestinal tuberculosis

“…31 Although the Xpert® MTB/Rif has emerged as an important tool for the diagnosis of pulmonary TB and some forms of EPTB (lymphadenitis), the reports on the use for ATB have indicated a limited benefit. 32 In a report on the use of Xpert in peritoneal TB, the test was positive in only 4 out of 21 patients who were diagnosed with peritoneal TB. 33 Similarly, in a report on ITB, only 3 out of 37 patients had a positive Xpert MTB/Rif test, suggesting that the sensitivity of the test for ATB would be low.…”

“…33 Similarly, in a report on ITB, only 3 out of 37 patients had a positive Xpert MTB/Rif test, suggesting that the sensitivity of the test for ATB would be low. 32 The yield of an in-house PCR (using three genes: hsp-66, esat-6, and ITS MAC) was also reported to be low. 34 The bulk of evidence therefore suggests that PCR-based tests also provide a low sensitivity for the diagnosis of ATB.…”