Role of CBNAAT in the Diagnosis of Extra-Pulmonary Tuberculosis: Experience from a Tertiary Care Hospital in India

ABSTRACT

Background. Xpert-MTB/RIF assay or Cartridge-Based Nucleic Acid Amplification Test (CBNAAT) helps in rapid diagnosis of tuberculosis (TB). Methods. Specific samples were collected and carried to Regional Medical Research Centre where these were taken up for CBNAAT and culture in Lowenstein-Jensen media. Appropriate samples were sent to the Designated Microscopy Centre (DMC) of our institute for acid-fast bacilli (AFB) smear examination. Diagnostic measures, such as sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of Xpert-MTB/RIF were reported considering mycobacterial culture and a composite reference standard (CRS) as Gold standard. Results. We studied 335 samples. Lymph node fine needle aspirate was the most common sample (32.5%) followed by pleural fluid (29.3%). The overall sensitivity and specificity of Xpert-MTB/RIF was determined to be 26.5% (95% CI [confidence interval] 20.8�.8) and 100% (95% CI 96.8�0), respectively. The sensitivity and specificity of CBNAAT in relation to mycobacterial culture, however, was 78.8% (95% CI 61.1�.0) and 89.1% (95% CI 85�.4), respectively. Both were highest for pus, cerebrospinal fluid and lymph node fine needle aspirate samples. Conclusions. Xpert-MTB/RIF may be useful for samples, like cold abscess and lymph node fine needle aspirate or biopsy specimens. However, its routine use in case of serosal fluids is not recommended because of its lower sensitivity.