To Test or Not? Xpert MTB/RIF as an Alternative to Smear Microscopy to Guide Line Probe Assay Testing for Drug-Resistant Tuberculosis

Abstract

Xpert MTB/RIF (Xpert) revolutionized tuberculosis (TB) diagnosis. Laboratory decision making on whether widely-used reflex drug susceptibility assays (MTBDR plus , first-line resistance; MTBDR sl , second-line) are conducted is based on smear status, with smear-negative specimens often excluded. We performed receiver operator characteristic (ROC) curve analyses using bacterial load information (smear microscopy grade, Xpert-generated semi-quantitation categories and minimum cycle threshold [C Tmin ] values) from Xpert rifampicin-resistant sputum for the prediction of downstream line probe assay results as “likely non-actionable” (no resistance or susceptible results generated).