Role of CBNAAT in diagnosis of new pulmonary TB cases under RNTCP: A Retrospective analysis from Ahmedabad, India

Abstract

Introduction and Aim: The World Health Organisation (WHO) TB statistics for India for 2016 give an estimated incidence of 2.79 million cases. CBNAAT (Cartridge based nucleic acid amplification Test) helps to diagnose upfront drug resistance within two hours of sample submission. Materials and Methods: We collected data from RNTCP laboratory for all newly diagnosed cases of Pulmonary TB registered from December 2018 to July 2019 who underwent sputum microscopy by LED FM and CBNAAT testing. Result: Out of 333 patients, 241 (72%) were sputum microscopy positive while CBNAAT detected Mycobacterium TB (MTB) in 289 (86.8%) patients of whom Rifampicin resistance was detected among 15 patients (4.5%). This included 12/240 sputum positive patients in whom MTB was detected by CBNAAT and 3/49 sputum negative patients in whom MTB was detected by CBNAAT. There is moderate agreement for diagnosis of MTB by CBNAAT and sputum microscopy (Kappa = 0.55, CI: 0.449 to 0.655). Conclusion: Universal upfront sputum CBNAAT in all new suspected cases of pulmonary TB according to current guidelines of RNTCP shows moderate agreement with LED-FM and yields a elevated percentage of patients being diagnosed with pulmonary sputum positive TB. Keywords: New Pulmonary TB, Sputum Microscopy, CBNAAT, Drug Resistant TB.