Evaluating Diagnostic Performance of Extrapulmonary Tuberculosis Using Cartridge-Based Nucleic Acid Amplification Test Assay: A Retrospective Cross-Sectional Study at a Tertiary Health Care Setup in India

Background: Extrapulmonary tuberculosis (EPTB) diagnosis is difficult due to its subclinical or nonspecific clinical symptoms, paucibacillary nature, and difficulties in obtaining qualified pathological specimens for Mycobacterium tuberculosis detection. Given the paucibacillary nature of EPTB, and drug resistance as high as 19%, rapid diagnostic methods like Xpert MTB/RIF (Cepheid, Sunnyvale, California, USA) can make a significant clinical impact. In this study, the authors aim to determine the positivity rate of Mycobacterium tuberculosis in EPTB samples by Xpert MTB/RIF or cartridge-based nucleic acid amplification test (CBNAAT) in a tertiary healthcare setup. Materials and methods: This was a retrospective cross-sectional study where presumptive extrapulmonary cases of any age were considered for inclusion. A total of 688 suspected extrapulmonary samples were analysed by CBNAAT over a period of 7 months. Result: A total of 25% (170/688) of the cases were reported to be positive, while the combined rate of Error, Invalid, and No result was 8.5% (59/688). Rifampicin resistance was seen in 14 isolates, while four isolates showed indeterminate results. Conclusion: Varied clinical presentations and the paucibacillary nature of the extrapulmonary samples often lead to the failure of diagnosis by conventional diagnostic tests (smear microscopy and culture). Hence, molecular diagnostic techniques play a crucial role in rapid diagnosis. The present study thus highlights the impact of CBNAAT in the definite diagnosis of extrapulmonary tuberculosis in a tertiary healthcare centre.