Non-actionable results, accuracy and effect of the first- and second-line line probe assays for diagnosing drug resistant tuberculosis, including on smear-negative specimens, in a high-volume laboratory.

MTBDRsl did not generate a result in almost half of smear-negative individuals (4/10 failed), resulting in substantial missed resistance. However, if MTBDRsl generates an actionable result, that result is accurate in ruling-in second-line resistance. Isoniazid susceptibility testing remains crucial. This study provides, in the context of WHO guidance, real-world direct second-line susceptibility testing performance data on non-actionable results (which, if unaccounted for, result in an overestimation of test utility), accuracy, and care cascade impact.