STUDY OF DIAGNOSTIC ACCURACY OF XPERT MTB/RIF IN PULMONARY TUBERCULOSIS IN A TERTIARY CARE TEACHING HOSPITAL, SVIMS, TIRUPATI, ANDHRA PRADESH

Objective: Tuberculosis is one of the major global health problems, while India contributing to a major chunk of the disease burden. A molecular method, the Xpert MTB/RIF (Cepheid, USA) can detect the presence of Mycobacterium tuberculosis DNA and the diagnostic accuracy of Xpert MTB/RIF in pulmonary tuberculosis was evaluated. Methods: This prospective study was conducted from September 2019 to September 2020. Sputum specimens were collected and processed for Ziehl Neelsen staining technique, culture on solid Lowenstein Jensen medium and Xpert MTB/RIF. Differentiation of NTM’s from MTB by was done by performing Rapid test method using TB antigen MPT64 immunoprotein antigen. Drug susceptibility testing by proportion method was performed. The data was compiled and analyzed statistically. The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of Xpert MTB/RIF was calculated using sputum culture for Mycobacterium tuberculosis as a gold standard test. Results: A total of 435 samples satisfying the inclusion criteria were processed and analyzed. Considering Mycobacterial culture as a “gold standard” the sensitivity, specificity and accuracy of Xpert MTB/RIF in the diagnosis of pulmonary tuberculosis was noted as 96.4% (95% CI 87.4%-99.5%), 93.3% (95%CI 93.8%-97.9%) and 96.3% (95% CI 94%-97.8%) respectively. Among 9 rifampicin resistance samples detected by Xpert MTB/RIF, only 7 (77.8%) were rifampicin resistant by DST; additional 2 samples were detected by Xpert MTB/RIF alone. Conclusion: The current study concluded that Xpert MTB/RIF is a first-line diagnostic tool in pulmonary tuberculosis which can be used in field settings as a point-of-care test and to be compared with clinical aspect of the patient as a part of National Tuberculosis Elimination Programme.