A study to analyze the differences between GeneXpert MTB/RIF assay and LED fluorescent microscopy for the diagnosis of pulmonary tuberculosis in a tertiary care centre

Abstract

Mycobacterium tuberculosis cultures although being the gold standard for diagnosing tuberculosis has its limitations as it is time consuming. Thus newer methods using light-emitting diode fluorescent microscopy (LED-FM) and molecular methods like the GeneXpert MTB/RIF assay are being adopted as a mainstay for diagnosing tuberculosis around the globe. Materials and Methods: This observational descriptive study was carried out for a period of 21 months. Sputum samples from 110 adult subjects with a clinical suspicion of pulmonary tuberculosis (PTB) were stained for LED-FM microscopy and also inoculated into the GeneXpert assay. The positive smears were graded as per the Revised National Tuberculosis Control Programme (RNTCP) guidelines and positive GeneXpert assay results along with Rifampicin resistance were noted and analysed. Results: Out of the 110 samples, (77.2%) were males and (22.7%) females. Of the 110 samples, 75 (68.1%) were positive for Mycobacterium tuberculosis by the GeneXpert assay. In contrast with LED-FM, all 25 smear positive samples were also GeneXpert positive. Additionally, GeneXpert detected 10 smear negative cases. 10 (9%) positive GeneXpert isolates showed resistance to Rifampicin. The overall sensitivity of GeneXpert was greater but its specificity was comparable with LED-FM. Conclusion:The Xpert and LED-FM tests were comparable in specificity, but the GeneXpert assay out did the LED-FM as it was a more sensitive and rapid test for the diagnosis of tuberculosis and additionally detection of Rifampicin resistance. Our study fully agrees that the GeneXpert assay is a step ahead in the early diagnosis of tuberculosis even for smear negative cases of PTB. This assay is also a relatively simple and routine test that staff can perform with minimal training.