Evaluation of Xpert MTB/RIF Ultra in differentiating tuberculosis from sarcoidosis in patients with mediastinal lymphadenopathy

<b>Background:</b> In patients with intrathoracic lymphadenopathy, differentiating tuberculosis from sarcoidosis is challenging. We evaluated the performance of Xpert MTB/RIF Ultra, a cartridge-based automated molecular test, for this purpose. <b>Methods:</b> This was a prospective study of subjects with intrathoracic lymphadenopathy who underwent endobronchial ultrasound (EBUS)-guided transbronchial needle aspiration (TBNA) and were diagnosed as either tuberculosis or sarcoidosis. The diagnosis was based on clinico-radiologic, pathologic, and microbiologic information. The results of Xpert MTB/RIF Ultra assay and multiplex polymerase chain reaction (mPCR) were compared between the two groups to calculate the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). <b>Results:</b> During the study period, 159 subjects underwent EBUS-TBNA with a clinical diagnosis of granulomatous mediastinal lymphadenopathy (GRAMA). A diagnosis of sarcoidosis (n=109) or tuberculosis (n=37) was made in 146 subjects (mean age 41.0 years; 73 [50.0%]). Xpert MTB/RIF Ultra was positive in 21 (56.8%) and six (5.5%) patients with tuberculosis and sarcoidosis, respectively. The sensitivity, specificity, positive and negative predictive values of Xpert MTB/RIF Ultra for diagnosing tuberculosis were 56.8 %, 94.5%, 77.8% and 86.5%, respectively. The respective performance characteristics for mPCR were 66.7%, 98.0%, 94.4%, and 84.8%. Mycobacterial culture was positive in only 7/37 (18.9%) subjects with tuberculosis. <b>Conclusions:</b> Xpert MTB/RIF Ultra has a low sensitivity and a good specificity for differentiating tuberculosis from sarcoidosis in suspected GRAMA.