Evaluation of the diagnostic performance of theXpert® MTB/RIF assay in pulmonary andextrapulmonary samples

Introduction: This study aimed to evaluate the performance of the Xpert\rMTB/RIF assay in the identification of M. tuberculosis in pulmonary and extrapulmonary clinical samples by taking the results of the BACTEC MGIT\r960TB culture system as a reference.\rMaterials and Methods: A total of 11,341 specimens sent to Sivas Cumhuriyet\rUniversity Application and Research Hospital Tuberculosis Laboratory for\rmicrobiological examination with suspicion of tuberculosis infection between\rJanuary 2013 and December 2019 were examined, and 6847 clinical specimens that underwent culture (BACTEC MGIT 960TB), Xpert MTB/RIF and\rAFB (Acid-fast bacilli) testing were selected and included in our study. Of the\rsamples included in the study, 5096 samples were pulmonary, and 1751 were\rextrapulmonary samples.\rResults: In our study, sensitivity, specificity, PPV and NPV values of Xpert MTB/\rRIF and AFB were calculated by taking TB culture test as reference test. The\rsensitivity of the Xpert MTB/RIF assay was calculated as 96.1%, specificity as\r99.7%, positive predictive value (PPV) as 88.2%, and negative predictive\rvalue (NPV) as 99.9%. These values for pulmonary samples were determined\ras 98.3%, 99.7%, 89.9%, and 99.9%, respectively. For extrapulmonary\rsamples, the sensitivity of the assay was found as 89.4%, specificity as 99.5%,\rPPV as 82.9%, and NPV as 99.7%. The sensitivity and PPV values for AFBpositive samples were found to be 99.0% and 97.1%, respectively. For AFB\rnegative samples, the sensitivity, specificity, PPV, and NPV values were determined as 90.5%, 99.7%, 73.8%, and 99.9%, respectively.\rConclusion: A large number of clinical samples were studied with the Xpert\rMTB/RIF test in our study. It can be a guide in determining the performance\rof the test under the conditions of our country. Especially in the diagnosis of\rextrapulmonary TB, the effectiveness of the Xpert MTB/RIF assay has not been\rcertainly proven in countries having a moderate prevalence of TB, such as Turkey. In most of the published studies, only a small part of the samples is extrapulmonary samples. So, our study provides valuable results in terms of evaluating a large number of extrapulmonary samples.