Determining the diagnostic potential of Truenat MTB Plus for Tubercular lymphadenitis and detection of drug resistance and a comparison with GeneXpert Ultra

Abstract

Setting: Tubercular lymphadenitis (TBLA), the most common form of extrapulmonary tuberculosis, is a diagnostic challenge.

Objective: Truenat MTB Plus (TruPlus) along with Truenat Rif assay (TruRif) was evaluated for detection of TBLA and rifampicin resistance and compared with GeneXpert Ultra (Xpert Ultra).

Design: 100 fine-needle aspirated specimens [50 confirmed by culture/smear/cytology, 20 clinically suspected, and 30 controls], processed in the mycobacteriology division of department of microbiology were subjected to TruPlus and TruRif, Xpert Ultra and multiplex PCR. The results of TBLA detection were compared against composite reference standard (CRS) and those of rifampicin resistance were compared against phenotypic drug susceptibility testing and rpoB gene sequencing.

Results: In comparison to CRS, the diagnostic yield of TruPlus, Xpert Ultra and MPCR was 77.14%, 59.18% and 84.28%, respectively; with substantial agreement for TruPlus (k = 0.66) and MPCR (k = 0.76) and moderate for Xpert Ultra (k = 0.60). TruRif reported four cases as RifR and Xpert Ultra reported two. On comparing with phenotypic DST and gene sequencing, only two cases of RifR were confirmed, hence TruRif reported false-RifR in two cases.

Conclusion: TruPlus could be used as a reliable tool for diagnosing TBLA. The reporting of RifR by TruRif should be confirmed by phenotypic DST or gene sequencing.

Keywords: Drug resistant TB; Lymph node tuberculosis; Lymphadenopathy; Molecular diagnosis; Rapid diagnosis.