g We compared 14 molecular assays for their ability to detect the Mycobacterium tuberculosis complex in bronchoalveolar lavage fluid samples. Three approaches were followed. First, by using DNA from Mycobacterium bovis BCG, we determined the detection limits of the assays using routine molecular methods. Second, in order to determine the analytical sensitivities of the assays, we added one of four M. tuberculosis isolates with various numbers of the insertion sequence IS6110 to N-acetyl-L-cysteine (NALC)-NaOH-treated bronchoalveolar lavage fluid samples in dilutions of 1:10 to 1:10,000,000. Third, intertest variabilities were measured and defined by the standard deviations for the quantitation cycle (Cq) values of three positive test results per dilution per assay. The 14 assays tested had similar analytical sensitivities, except for GeneXpert, which had an analytical sensitivity that was 10-to 100-fold lower than that of the other assays. The MP MTB/NTM test and the in-house TaqMan-10 revealed the best performances for the detection limit and had the highest analytical sensitivities. Most of the tests performed well regarding detection limit and analytical sensitivity for the detection of the M. tuberculosis complex in serial dilutions, and the differences were small. The MP MTB/NTM and the in-house TaqMan-10 assays revealed the best, and GeneXpert the worst, overall performances. I n 2011, 6.2 million patients were diagnosed with tuberculosis (TB) worldwide and reported this to the national tuberculosis control programs (NTP) (1). Control of this high-burden disease heavily depends on improved rapid diagnosis and optimal treatment. Real-time (RT)-PCR is the standard DNA amplification technique currently used in TB laboratories. In a short time span, a substantial number of commercial nucleic acid amplification tests for Mycobacterium tuberculosis complex (MTC) infections have become available. However, these assays have not been compared in a systematic manner. The clinical sensitivity of a part of the assays has been reported in only a few studies, using culture positivity and/or clinical diagnosis as the "gold standard" (2-6).The insertion sequence IS6110 has long been appreciated as a target in the molecular detection of the M. tuberculosis complex in clinical material, and it is the most abundant IS element in the genome of M. tuberculosis. However, among clinical isolates worldwide, the number of IS6110 copies in the genome of M. tuberculosis varies from 0 to 25, potentially influencing the detection limits of related assays (7-10).In this study, we compared the analytical performances of 14 assays for the molecular detection of MTC in three different approaches. We hypothesized that not all assays would have equally good analytical sensitivities and that the analytical sensitivity of assays targeting IS6110 would depend on the number of target copies in the genomes of M. tuberculosis strains studied. We therefore compared IS6110-targeting tests with those not targeting this element or that explored unkno...