Diagnosis of extrapulmonary tuberculosis by Truenat® MTB/MTB Plus assay

Abstract

Diagnosis of extrapulmonary tuberculosis (EPTB) is challenging. During the last two decades, several nucleic acid amplification tests have been deliberated to diagnose TB (including EPTB) and drug resistance (DR), i.e. in-house PCR/multiplex-PCR, commercial real-time PCR (e.g. Cobas TaqMan/LightCycler), line probe assay (e.g. GenoType MTBDRplus), GeneXpert®/GeneXpert® Ultra and Truenat®MTB/MTB Plus (TruPlus). However, we still need a simple and reliable diagnostic test especially for remote areas. Markedly, both GeneXpert/Xpert Ultra require a constant power supply and their high cost is a major hindrance in resource-limited settings. To overcome this, Molbio Diagnostics, India, introduced a Truenat/TruPlus assay (the WHO endorsed), which is chip-based micro real-time PCR system that targets nrdB, while TruPlus targets IS6110+nrdZ for the identification of Mtb within 1 h. After a positive result, an ‘add-on’ chip, i.e. Truenat® MTB-RIF Dx (TruRif) is utilized to detect rifampicin-resistance (RIF-R) that takes another 1 h. Although there is adequate literature on the diagnosis of pulmonary TB by Truenat/TruPlus, limited information is available on EPTB diagnosis. In this review, we assessed the performance of Truenat/TruPlus in different EPTB types, i.e. TB lymphadenitis, TB pleuritis, TB meningitis, osteoarticular TB, etc. that exhibits moderate to good sensitivity/specificity. Meanwhile, few false negative/positive RIF-R results are obtained by TruRif. Since Truenat/TruPlus is portable, battery-operated and relatively cost-effective as compared to GeneXpert/Xpert Ultra, it can be utilized for preliminary screening of EPTB specimens in peripheral settings, which may be further confirmed by other tests.