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

Our plain-English summary of Tissue Xpert™ MTB/Rif assay is of limited use in diagnosing peritoneal tuberculosis in patients with exudative ascites, by C. Bera, J.S. Michael, D. Burad, et al (Indian Journal of Gastroenterology, 2015).

The study

• Authors: C. Bera, J.S. Michael, D. Burad, S.B. Shirly, S. Gibikote, B. Ramakrishna, A. Goel, C.E. Eapen
• Journal: Indian Journal of Gastroenterology
• Published: 2015;34(5):395-8
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

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.

In plain English

This study, from the liver clinic of Christian Medical College, Vellore, India, tested how well a rapid DNA-based tuberculosis test (Xpert MTB/Rif) diagnosed tuberculosis of the abdominal lining when run on omental biopsy tissue. It enrolled 28 outpatients between January 2012 and July 2013. All had exudative ascites, a protein-rich fluid build-up in the abdomen. On three repeated fluid tests, smears were stained for acid-fast bacilli (the group of bacteria that includes tuberculosis) and for cancer cells, and found neither. The test was compared against a combined standard of culture, biopsy findings and response to tuberculosis treatment. By that standard, 21 patients had peritoneal tuberculosis. Seven had other diagnoses, including mesothelioma in 2. The article does not discuss asbestos. The test was positive in 4 of the 21 tuberculosis patients and in none of the 7 others. That gave a sensitivity of 19% (95% C.I: 6% to 42%) and a specificity of 100% (95% C.I: 59% to 100%). The authors concluded that the tissue test, though specific, cannot be recommended for diagnosing peritoneal tuberculosis. They noted that the study included only a small number of patients.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Diagnostic accuracy study comparing the tissue Xpert MTB/Rif assay against a composite reference standard (microbiology, histology, treatment response)
• Who was studied: 28 outpatients (20 male, 8 female; mean age 43, SD 15 years) with exudative ascites attending the liver clinic of Christian Medical College, Vellore, India, January 2012 to July 2013. Their ascitic fluid was negative on three repeated smears for acid-fast bacilli (auramine O fluorescence stain) and for malignant cells (Papanicolaou stain). 4 had underlying cirrhosis.
• Exposure: No asbestos or other exposure was studied; the study evaluated the Xpert MTB/Rif test performed on ultrasound-guided omental biopsy tissue
• Main results:
  • 21 of the 28 patients were diagnosed with peritoneal tuberculosis by the reference standard
  • 7 patients (25%) had alternative diagnoses on omental biopsy: metastatic carcinoma 2, adenocarcinoma 2, mesothelioma 2, systemic lupus erythematosus 1
  • The Xpert test was positive in 4 of the 21 patients (19%) with peritoneal tuberculosis
  • The Xpert test was negative in all 7 patients with alternative diagnoses
  • For diagnosing peritoneal tuberculosis, the tissue Xpert test had sensitivity 19% (95% C.I: 6% to 42%), specificity 100% (95% C.I: 59% to 100%), positive predictive value 100% (95% C.I: 40% to 100%) and negative predictive value 29% (95% C.I: 13% to 51%)
  • Among the 4 culture-positive patients, the Xpert test was positive in 2 (50%)
  • The Xpert test detected rifampicin resistance in two patients
• The authors' conclusion: The authors concluded that the tissue Xpert MTB/Rif assay, though specific, cannot be recommended for diagnosing peritoneal tuberculosis
• Limitations the authors state:
  • The estimates are based on a small number of patients and need validation in larger samples
  • Laparoscopy-assisted peritoneal biopsy, which might increase microbiological yield, was not done
  • Ascitic fluid adenosine deaminase (ADA) testing was not done

Topics

Medical terms in this study, explained in our Lexicon: Ascites, Fluid Cytology, Ultrasound, Biopsy, Inflammation, Histology, Carcinoma, Adenocarcinoma.

Related studies

• Expression Profiles of Cytokine mRNAs in the Pleural Fluid Reveal Differences Among Tuberculosis, Malignancies, and Pneumonia-Exudative Pleural Effusions — D.L. Espósito, V.R. Bollela, et al. (2015)
• A Single-Center Experience: The Diagnostic Role of Peritoneoscopy in Patients with Exudative Ascites — B. Abaylı, G. Gençdal (2019)
• An unusual case of ascites: pitfalls in diagnosis of malignant peritoneal mesothelioma — J.R. Clark, W.B. Ross (2000)
• The role of peritoneal biopsy in the diagnosis of ascites — P.F. Jenkins, M.J. Ward (1980)
• The role of "closed abdomen" hyperthermic intraperitoneal chemotherapy (HIPEC) in the palliative treatment of neoplastic ascites from peritoneal carcinomatosis: report of a single-center experience — L. Orgiano, F. Pani, et al. (2016)
• "Signet-ring" cells--a caveat in the diagnosis of a diffuse peritoneal mesothelioma occurring in a lady presenting with recurrent ascites: an unusual case report — B. Rekhi, S. Pathuthara, et al. (2010)

Browse return to medical research.