Xpert Ultra in diagnosing extrapulmonary TB: accuracy and trace calls

INTRODUCTION: Xpert Ultra (Ultra) was developed to improve the detection of TB; however, data on Ultra´s diagnostic accuracy in extrapulmonary TB (EPTB) are limited. METHODS: In this prospective diagnostic accuracy study, 242 EPTB samples were subjected to Ultra and Xpert MTB/Rif (Xpert) testing, and these were compared with both culture and a composite gold standard. RESULTS: Compared to culture, Ultra sensitivity and specificity using bone, cerebrospinal fluid (CSF), lymph node and tissue samples, and overall were respectively 100% and 77.3%, 75% and 100%, 87.5% and 87.5%, 100% and 87%, and 89.7% and 87.4%; in comparison to the composite gold standard, Ultra´s sensitivity and specificity were respectively 66.7% and 100%, 17.6% and 100%, 46.9% and 95.7%, 38.5% and 94.1%, and 46.2% and 96.9%. Using latent class analysis, sensitivity and specificity were respectively 94.5% and 96.3% for Ultra, 65.5% and 99.8% for Xpert, and 58.6% and 99.2% for culture. There were 22/242 (9%) trace calls on Ultra. CONCLUSION: We found improved sensitivity for Ultra compared to Xpert, although Ultra specificity was lower, with a large number of trace results (9%).