The rapid molecular test Xpert MTB/RIF ultra: towards improved tuberculosis diagnosis and rifampicin resistance detection

Abstract

Background: Tuberculosis diagnosis has dramatically improved since the introduction of the rapid molecular test Xpert MTB/RIF (Xpert) detecting M. tuberculosis and rifampicin resistance directly from clinical specimens, therefore shortening the turnaround time, reducing patient's isolation period and decreasing the time to start anti-TB drugs. The new version, Xpert MTB/RIF Ultra (Ultra), displays a higher sensitivity and an improved rifampicin resistance detection. Both tests have been endorsed by the World Health Organisation.

Aims: Xpert and Ultra rapidly became widespread and paved the way for new approaches and new paradigms as well as for the development of molecular point-of-care tests (POCTs). In this narrative review, we aimed to address their performance in the diagnosis of tuberculosis and to discuss the expectations of these tests as well as their limits and the unmet needs.

Sources: Peer-reviewed publications addressing the diagnostic performance of Ultra and Xpert.

Content: We focused on publications that evaluated the performance of Ultra and Xpert on the same group of patients or the same set of specimens in different tuberculosis-burden settings.

Implications: The studies published so far reported an increased sensitivity of Ultra when compared to Xpert, which represents a benefit for tuberculosis diagnosis. The fact that such a sensitive assay cannot distinguish between alive and dead bacilli emphasizes that caution should be exercised regarding indications and interpretation of results. Additional studies are needed to determine the true performance for the diagnosis of extrapulmonary tuberculosis because of the great diversity of the specimens.

Keywords: HIV; Molecular diagnostics; Paediatric tuberculosis; Pleural tuberculosis; Point of care test; Rifampicin resistance; Tuberculosis; Tuberculous meningitis; Xpert MTB/RIF; Xpert MTB/RIF Ultra.