Diagnostic Performance of Xpert MTB /RIF in Comparison with LED Fluorescence Microscopy and Culture in Suspected Cases of Pulmonary Tuberculosis

GeneXpert MTB/RIF assay (GeneXpert) is relatively new technology in India and it is important to generate data on its efficacy for diagnosis of Tuberculosis. Thus; present study was undertaken to compare the diagnostic performance of GeneXpert for diagnosis of pulmonary tuberculosis (PTB) in comparison with Auramine O staining based Light Emitting Diode- Fluorescence Microscopy (LED-FM) considering culture as gold standard. A total of 662 (451 BAL, 211 Sputum) respiratory samples obtained from patients suspected of PTB were tested for smear microscopy and GeneXpert assay and were compared with culture results. Rifampicin resistance was compared with Genotype MTBDR plus assay. Sensitivity, specificity, positive predictive value (PPV) and negative predictive values (NPV) of the assays were calculated using SPSS version 22. On comparing with culture the sensitivity, specificity, PPV and NPV of GeneXpert MTB/RIF was found to be 97.25%, 98.54%, 96.20% and 98.95% respectively whereas sensitivity, specificity, PPV and NPV of smear microscopy was found to be 73.08%, 100%, 100% and 90.74% respectively. Rifampicin resistance was detected in 11 (1.66%) samples by GeneXpert. Five (0.75%) samples among them were found to be MDR whereas one sample showed false positive result for rifampicin resistant when compared by Genotype MTBDR plus assay. GeneXpert MTB/RIF assay offers much higher sensitivity as compared to Auramine O staining based LED-FM and seems to be a promising tool for TB diagnosis. Further longitudinal studies are required to evaluate the potential of this assay at primary health care settings and diagnosis of Extrapulmonary TB