A comparative study of the diagnostic efficacy of CB-NAAT and ZN staining

Background:In recent years,cartridge based nucleic acid amplification test(CBNAAT)has been recommended by World Health Organization as a rapid diagnostic test for detection of tuberculosis and rifampicin resistance. Aim: In this study, we retrospectively compared results for diagnosis of suspected pulmonary and Extrapulmonary tuberculosis cases, from March 2020 to September 2020 for Ziehl-Neelsen(ZN)and GeneXpert (Xpert®MTB/Rif assay)taking culture as gold standard. Methods: Performance of Xpert was compared to acid-fast microscopic examinationusingZiehl-Neelsen (ZN) stain in patients with culture-confirmed tuberculosis.Results: Out of total 914 specimens of clinically suspected patients of tuberculosis of all age groups,683(75%) were pulmonary specimens and231(25%)were extrapulmonary. For pulmonary samples, the sensitivity and specificityfor CBNAAT samples were 82.3%and98.5%while that for sputum smear were 63.7% and 99.3% respectively.For extrapulmonary samples,the sensitivity and specificity for CBNAAT samples were 85.7% and 93.5% respectively; while that for sputum smear were 60.7%and100% respectively. Conclusion: Although the development of the Xpert MTB/RIF assay is undoubtedly alandmarkeventina high TB burden country like India as this test will help in rapiddiagnosis of smear-negative and rifampicin resistant TB cases, which were earlier a challenge for the TB control programme