Rapid diagnosis of drug-resistant TB using line probe assays: from evidence to policy.

Growing concerns about the spread of multidrug-resistant tuberculosis (MDR-TB) and the emergence of extensively drug-resistant TB have triggered substantial interest in the development and application of rapid tests for the detection of drug-resistant TB. Molecular assays to detect gene mutations that signal drug resistance are widely recognized as being most suited for rapid diagnosis. Among molecular assays, line probe assays have shown great promise. Currently, two line probe assays are commercially available: the INNO-LiPA Rif. TB kit (Innogenetics NV, Gent, Belgium) and the GenoType MTBDRplus assay (Hain Lifescience GmbH, Nehren, Germany). Evidence from a systematic review suggests that INNO-LiPA is a highly sensitive and specific test for the detection of rifampicin resistance in culture isolates. The test, however, appeared to have relatively lower sensitivity when used directly on clinical specimens. Another meta-analysis showed that the GenoType MTBDR assays had excellent accuracy for rifampicin resistance, even when used directly on clinical specimens. While specificity was excellent for isoniazid, sensitivity estimates were modest and variable. Based on evidence and expert opinion, the WHO recently endorsed the use of molecular line probe assays for rapid screening of patients at risk of MDR-TB. Special initiatives have been announced to make these assays accessible and affordable for countries with high MDR-TB prevalence. With strong evidence and new policy directives, the stage is now set for the use of rapid tests for MDR-TB diagnosis. Whether molecular tools, such as line probe assays, will actually make a clinical and public-health impact remains to be determined.