The conventional drug sensitivity test is traditionally used in Brazil to diagnose drug-resistant tuberculosis. However, the test can take up to 60 days to return a diagnosis, which is considered too long for certain vulnerable populations. Therefore, this study analyzed the available scientific evidence on the accuracy and time to diagnosis of the nitrate reductase assay for diagnosing resistant tuberculosis, compared with the conventional drug sensitivity test.

We searched MEDLINE, Embase, and The Cochrane Library for systematic reviews with meta-analyses. The articles were screened by title and abstract. The full-texts of potentially relevant articles were then screened according to the inclusion criteria.

Three systematic reviews with meta-analyses were selected that compared the nitrate reductase assay with the conventional drug sensitivity test. The accuracy of the nitrate reductase assay was satisfactory in most of the results when compared with the sensitivity test, except for one study that showed low sensitivity for the detection of streptomycin resistance. In addition, the nitrate reductase assay had a shorter time to diagnosis than the drug sensitivity test.

The results of this study reinforce the idea that the nitrate reductase assay may diagnose drug-resistant tuberculosis earlier than the conventional drug sensitivity test and be a helpful strategy for controlling the disease, especially in vulnerable populations that are more likely to be affected by tuberculosis. For a broader analysis of the benefit of the assay, it is suggested that studies investigate the impact of the shorter time to diagnosis on morbidity and mortality in patients with drug-resistant tuberculosis. In addition, economic analyses comparing the nitrate reductase assay with the sensitivity test are recommended to evaluate the cost-benefit ratio.