Comparison of the Xpert MTB/RIF Assay and Real-time PCR for the Detection of Mycobacterium tuberculosis

Introduction. We compared the Xpert MTB/RIF assay with a real-time PCR assay using samples from culture-positive patients with TB. In addition, drug susceptibility test results were compared to evaluate the usefulness of these methods. Materials and Methods. Fifty-two clinical specimens were analyzed by standard smear-microscopy, mycobacterial growth indicator tube (MGIT) culture, solid culture, MGIT drug-susceptibility testing, TB real-time PCR, and the Xpert MTB/RIF assay. Results. Diagnostic sensitivity of AdvanSure TB/NTM real-time PCR was 80.0%. As shown from smear positive and negative specimens, sensitivities were 87.5% and 75.9%, respectively. The diagnostic sensitivity of Xpert MTB/RIF assay was 75.5%, and from smear positive and negative specimens, sensitivities were 93.8% and 65.5%, respectively. There were 10 cases with discrepant results between two methods. 2 cases were found resistant to rifampin, although Xpert MTB/RIF assay was able to detect rifampin resistance in only one specimen. Discussion. Xpert MTB/RIF assay is an easier method to conduct and while its ability to detect rifampin resistance simultaneously is a benefit, its sensitivity from smear negative-culture positive specimens was lower than Advansure TB/NTM real-time PCR. Further investigation to increase the sensitivity and detect other drug resistances by kit-based assays is required for the rapid and accurate diagnosis of tuberculosis.