Molecular WHO-recommended rapid diagnostic tests for TB

The Xpert MTB/RIF assay is a cartridge-based automated test that uses real-time polymerase chain reaction (PCR) on the GeneXpert® platform to identify M. tuberculosis complex and mutations associated with rifampicin resistance directly from sputum specimens in less than 2 hours (76).

The Xpert MTB/RIF Ultra assay uses the same GeneXpert platform and a new enhanced cartridge developed to improve the sensitivity and reliability of detection of M. tuberculosis complex and rifampicin resistance (76).

Trace results are common with the use of Xpert Ultra in all paediatric specimen types, reflecting the paucibacillary nature of TB disease in children. For children and people living with HIV being evaluated for PTB, and for people being evaluated for EPTB, the “M. tuberculosis complex detected trace” Ultra result is considered bacteriological confirmation of TB (76). This is an important implementation consideration, considering the risk of morbidity and mortality in these populations. Trace results have an indeterminate result for rifampicin resistance, and alternative specimens may need to be collected for Xpert Ultra processing in people with a high likelihood of drug resistance.

The Truenat MTB and MTB Plus assays use chip-based real-time micro-PCR for the semiquantitative detection of M. tuberculosis complex directly from sputum specimens and can report results in less than an hour. The assays use automated battery-operated devices to extract, amplify and detect specific genomic DNA loci. The assays are designed to be operated in peripheral laboratories with minimal infrastructure and minimally trained technicians. If the assay result is positive, an aliquot of extracted
DNA is run on the Truenat MTB-RIF Dx assay to detect mutations associated with RIF resistance (76).

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