Utility of CBNAAT (GeneXpert MTB/RIF assay) in rapid diagnosis of extrapulmonary tuberculosis in a hepatobiliary tertiary center

Abstract

Objectives Newer diagnostic techniques like cartridge-based nucleic acid amplification techniques (CB NAAT) need to be evaluated for extrapulmonary tuberculosis (EPTB), as being a paucibacillary condition, it is often underdiagnosed with conventional methods. We conducted this study to assess the utility of CB NAAT (GeneXpert MTB/RIF assay) in rapid diagnosis of extrapulmonary tuberculosis. Material and Methods Liver disease patients admitted from June 2019 to June 2020 were investigated for EPTB based on clinical and radiological suspicion. EPTB was diagnosed based on one of the following: (i) histological evidence of caseating granulomas; (ii) smear positivity for acid-fast bacilli; (iii) CB NAAT (GeneXpert MTB/RIF assay, Cepheid, USA). Results A total of 290 EPTB specimens received in the laboratory were included. The extrapulmonary samples that were received included body fluids (n = 143) which included pleural fluid, ascitic fluid, drain fluids, and pus aspirates, followed by biopsies (n = 82), lymph nodes (n = 43), urine (n = 19), and CSF (n = 3). GeneXpert MTB/RIF assay was positive in 10.3% (n = 30) samples, whereas negative in 89.7% (n = 260) samples. The overall sensitivity of GeneXpert MTB/RIF assay was 61.36% (95% CI 46.62%–74.28%), specificity 89.29% (95% CI 72.8%–96.29%), positive predictive value (PPV) 90% (95% CI 74.38%–96.54%), and negative predictive value (NPV) 59.52% (95% CI 44.49%–72.96%). Conclusion The GeneXpert MTB/RIF assay is a valuable tool for extrapulmonary tuberculosis. In addition to other tests like smear, culture GeneXpert MTB/RIF assay helps in the confirmation of diagnosis. Rapid diagnosis of tuberculosis with overall good sensitivity and specificity makes it a beneficial test.