Evaluation of GeneXpert MTB/RIF Assay for the Diagnosis of Tuberculosis and Rapid Detection of Rifampicin Resistance in Clinical Specimens

Abstract

Objectives: The aim of this study was to determine the performance of GeneXpert MTB/RIF (Xpert; Cepheid, Sunnyvale, CA) assay for the diagnosis of tuberculosis and rapid detection of rifampin resistance in clinical specimens. Materials and Methods: A total of 232 clinical specimens of 228 patients were included in the study. The GeneXpert MTB/RIF was used according to the instructions of the manufacturer. The results obtained by the GeneXpert MTB/RIF assay were then compared with the results obtained by culture, clinical diagnosis and phenotypic drug susceptibility testing (DST). Diagnosis of respiratory and nonrespiratory tuberculosis were confirmed by clinical (productive cough, hemoptysis, weight loss), pathological and radiographic findings and/or positive culture and microscopy tests. The final diagnosis for the culture-negative patients was established by the clinicians. Results: A total of 232 clinical specimens which 28 smear-positive and 204 smear negative were included in the study. Among all culture positive clinical specimens direct MTB/RIF test identified 56 of 69 specimens (NPV: %92,4 PPV: %93,3). In 27 of 28 (26 culture positive) smear positive specimens and 30 of 204 (42 culture positive)smear negative clinical specimes were correctly identified by the test. GeneXpert MTB/RIF assay detected 41 of 137 (40 culture positive) respiratory specimen (NPV: %94,8, PPV: %97,6). In 19 of 95 (16 culture positive) nonrepiratory specimens PCR was positive (NPV: %89,5, PPV: %84,2). When we evaluate the performance of PCR for the diagnosis of clinically diagnosed 83 tubercuosis cases (71 culture positive, 12 culture negative) NPV: % 87,3 and PPV: % 100. It had lower sensivity in nonrespiratory specimens (Table1). GeneXpert MTB/RIF assay did not detect any RIF resistance and it was confirmed by DST. Discussion: In conclusion, GeneXpert MTB/RIF assay could be useful to rapidly diagnose M. tuberculosis especially for smear negtive and smear positive respiratory specimens. However, in nonrespiratory specimens it has lower sensivity.