Comparative Evaluation of Cartridge-based Nucleic Acid Amplification Test Smear Microscopy and Conventional Culture Techniques in Laboratory Diagnosis of Tuberculosis

Aim: This study compared the nucleic acid amplification assay with smear microscopy and culture to assess the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) in patients with suspected pulmonary and extrapulmonary tuberculosis (TB) using pulmonary and extrapulmonary samples.Methods: The information for this retrospective study was collected from the Path Kind Laboratory-a National Accreditation Board for Testing and Calibration Laboratories (NABL) accredited lab in Gurugram, Haryana, India.We evaluated 1,520 samples with suspected TB for smear microscopy, culture, and GeneXpert between January 2019 and December 2020.These samples came from the pulmonary and extrapulmonary areas.Smear microscopy and GeneXpert's diagnostic capabilities for pulmonary and extrapulmonary TB were calculated, with Mycobacterium tuberculosis (MTB) culture from pulmonary and extrapulmonary specimens serving as the gold standard.Results: This study comprised 1,520 clinical samples altogether.Of these, 624 were extrapulmonary specimens, while 896 were pulmonary samples.Overall, acid-fast bacilli (AFB) smear microscopy's sensitivity, specificity, PPV, and NPV were 83.72, 91.91, 71.38, and 95.91%, respectively.Also, GeneXpert has overall values of 96.94, 81.22, 55.42, and 99.10% for sensitivity, specificity, PPV, and NPV, respectively. Conclusion:In both pulmonary and extrapulmonary specimens, the GeneXpert assay was shown to be a quick and reliable approach for detecting M. tuberculosis.Because GeneXpert can detect M. tuberculosis and rifampicin resistance in the same 2 hours as smear microscopy and MTB culture, it offers an advantage over those methods.Clinical significance: The early detection of TB can be greatly aided by the cartridge-based nucleic acid amplification test (CBNAAT).As an important part of the National Tuberculosis Elimination Program gene experts will certainly help in the elimination of tuberculosis from India.