Truenat MTB Plus Assay for Diagnosing Extrapulmonary Tuberculosis and Detecting Resistance to Rifampicin and Isoniazid

Truenat MTB Plus assay along with dedicated chips for rifampicin and isoniazid can aid in TB elimination efforts by establishing diagnosis of drug-resistant extrapulmonary tuberculosis (EPTB). 600 EPTB samples (125 microbiologically-confirmed, 275 clinically-suspected and 200 controls) processed between January 2019 and June 2023 were subjected to Truenat MTB Plus for detection of Mycobacterium tuberculosis. All samples showing presence of M. tuberculosis were subjected to individual chips for rifampicin and isoniazid detection. They were also subjected to Xpert MTB/RIF Ultra assay (XpertUltra). The sensitivity, specificity, positive and negative predictive value of Truenat MTB Plus for detecting EPTB was 73.5%, 100%, 100% and 65.3%, respectively, while that of XpertUltra was 69.2%, 100%, 100% and 61.9%, respectively. Their performance was comparable (p = 0.087), though the overall agreement with composite reference standard was substantial for Truenat MTB Plus (κ = 0.64) and moderate for XpertUltra (κ = 0.60). 18 cases of EPTB were detected only by Truenat MTB Plus and one only by XpertUltra. TruRif reported all 18 cases of RifR while XpertUltra reported 14. Two cases of false-RifR and four of false-InhR were reported by drug chips of Truenat MTB Plus. Truenat MTB Plus, along with its chips for detecting drug resistance, outperformed XpertUltra as it not only detected 18 additional cases but also enabled detecting resistance to isoniazid, in addition to rifampicin.