Evaluation of BACTEC™ MGIT™ 960 and the nitrate reductase assay in the National Laboratory Network of Colombia

SETTING: The Mycobacteria Group of the National Reference Laboratory, National Laboratory Network, National Institute of Health and the Public Health Laboratories of Antioquia, Atlántico and Valle del Cauca, Colombia.OBJECTIVE: To compare BACTEC™ MGIT™ (Mycobacteria Growth Indicator Tube) 960 and the nitrate reductase assay (NRA) with the proportion method on Löwenstein-Jensen medium and to determine resistance to first-line anti-tuberculosis drugs.METHODS: Evaluation of diagnostic assays using time-adjusted convenience sampling. We analysed 183 isolates of Mycobacterium tuberculosis to compare MGIT 960 and NRA with the proportion method.RESULTS: MGIT 960 had a sensitivity and specificity of 90% for isoniazid (INH), and respectively 100% and 99.4% for rifampicin (RMP). NRA had a sensitivity and a specificity of respectively 86% and 94.7% for INH and 100% and 99% for RMP.CONCLUSION: Given its high sensitivity and specificity, and easy accessibility and interpretation of results, the NRA should be implemented in the National Laboratory Network for the detection of resistance to INH and RMP.