Sensitivity and Specificity of Xpert MTB/RIF for Diagnosis of Pulmonary Tuberculosis, Detection of RIF Resistance and its Concordance with Gene Sequencing for RIF Resistance

Background: Mycobacterium tuberculosis remains one of the most significant causes of death from an infectious agent. The rapid diagnosis of tuberculosis and detection of rifampicin (RIF) resistance are essential for early disease management. The diagnostic accuracy of GeneXpert need is an important issue to be considered. Objective: To determine the diagnostic accuracy of GeneXpert in the diagnosis of rifampicin resistance in pulmonary tuberculosis keeping the culture-based test as gold standard for drug sensitivity. Material and methods: A cross-sectional validation study was conducted in pulmonology department of PIMS, Islamabad. The study sample size was 352 calculated by using WHO formula. The study duration was 6 months (Oct 2015-March 2016). Non-Probability consecutive sampling was done for selection of participants. Consent forms were taken from all the participants. Results: The study found out that out of all participants 352 (100%), there were 169 (48%) females and 183 (52%) males. The mean age of participants was 29.3 +/- 11.5 SD. The sensitivity of expectorated sputum was 98.5 (94.7-98.2), specificity was 50 (49.2-42.9), positive predictive value was 98 (98.5-99.9) and negative predictive value was 50 (49.3-41.0). A statistically significant association was found between culture, age, gender, recurrence, and treatment failure (p<0.05). Conclusion: Our study highlights that Xpert MTB/RIF has high sensitivity and moderate specificity for diagnosis of pulmonary tuberculosis, high rates of detection of RIF resistance and greater concordance with gene sequencing for RIF resistance when compared with culture.