The TB-Biochip oligonucleotide microarray system is a rapid system to detect mutations associated with rifampin (RIF) resistance in mycobacteria. After optimizing the system with 29 laboratory-generated rifampinresistant mutants of Mycobacterium tuberculosis, we evaluated the performance of this test using 75 clinical isolates of Mycobacterium tuberculosis. With this small sample set, the TB-Biochip system displayed a sensitivity of 80% and a specificity of 100% relative to conventional drug susceptibility testing results for RIF resistance. For these samples (ϳ50% tested positive), the positive predictive value was 100% and the negative predictive value was 85%. Four of the seven observed discrepancies were attributed to rare and new mutations not represented in the microarray, while three of the strains with discrepant results did not carry mutations in the RIF resistance-determining region. The results of this study confirm the utility of the system for rapid detection of RIF resistance and suggest approaches to increasing its sensitivity.The emergence of multidrug-resistant tuberculosis (MDR TB) presents a threat to global TB control efforts (15,19,20). MDR TB is defined as resistant to at least isoniazid and rifampin (RIF), the two most active first-line antimicrobial agents against TB (19,20). Rapid and reliable drug susceptibility testing is essential for the prompt initiation of appropriate therapy, which rapidly renders patients noninfectious and hence facilitates infection control measures to halt transmission (1).Rifampin is the mainstay of short-course chemotherapy for TB, and the loss of rifampin as an effective drug leads to a need for a longer duration of therapy and often to a lower cure rate (19,20). In Mycobacterium tuberculosis, resistance to RIF results from mutations in the  subunit of RNA polymerase, which is encoded by the rpoB gene (2,15). Approximately 95% of RIF-resistant strains carry mutations within the RIF resistance-determining region (RRDR), an 81-bp region carrying codons 507 through 533 of the rpoB gene (9,10,15). In this study, the TB-Biochip oligonucleotide microarray system (10) (Engelhardt Institute of Molecular Biology, Moscow, Russia) was used to detect RIF resistance among TB clinical isolates within a 24-hour period.The TB-Biochip oligonucleotide microarray system is designed to detect and identify 29 codon substitutions and 1 codon deletion distributed over 10 codon positions within the RRDR (10) (Fig. 1). These 30 mutations are found in Ͼ90% of RIF-resistant strains that have mutations in the RRDR (3-6, 10, 15). Each element (an acrylamide gel pad) of the microarray contains an immobilized oligonucleotide whose sequence matches that of either a wild-type or mutated segment of the RRDR. The use of acrylamide gel pads reduces the cost of each microarray to less than five U.S. dollars and increases the amount of oligonucleotide target that is present on the microarray, which increases the robustness of the hybridization reaction. Hybridization of the microarray with fluo...
BNP immunoassays. We found better agreement between the results obtained with the IRMA and ADVIA methods ( Fig. 1D; see also Fig. 1D in the online Data Supplement). We also observed a significant difference between the results obtained with these two methods (P ϭ 0.0032); the mean (SD) difference was 2.1 (140.8) ng/L.All immunoassay methods could differentiate between healthy individuals and patients with different degrees of heart failure as well as between patients with mild (NYHA classes I and II) and severe (NYHA classes III and IV) heart failure ( Table 1B).We tested the diagnostic accuracy of immunoassay methods for BNP and NT-proBNP by ROC curve analysis. All immunoassay methods clearly differentiated between the group of healthy individuals and the two groups of cardiac patients with mild (NYHA classes I and II) or severe (NYHA classes III and IV) heart failure [areas under the curves (AUC), 0.865-0.999]. The electrochemiluminescence immunoassay for NT-proBNP (AUC ϭ 0.954; 95% confidence interval, 0.920 -0.978) showed the best power, compared with the other immunoassays (AUC values ranging from 0.865 for the ADVIA to 0.902 for the IRMA; P Ͻ0.01), for separating healthy individuals from patients with mild symptoms of heart failure. The MEIA method showed different diagnostic characteristics compared with other the BNP immunoassays (McNemar 2 test, P ϭ 0.0036 vs ADVIA, 0.0083 vs IRMA, and 0.0153 vs POCT TRIAGE) in this group of patients, whereas there were no significant differences in performance among the other immunoassays. All immunoassay methods performed well (AUC values, 0.982-0.999) in differentiating between healthy individuals and patients with severe heart failure.The main goal of this study was to evaluate the analytical performance of several BNP and NT-proBNP immunoassays in samples subjected to the same preanalytical conditions. This protocol was chosen to better focus on performance differences among the tested methods to reduce as much as possible the other confounding causes of variability typical of multicenter studies or metaanalysis of published data. However, the clinical results of this study cannot be extrapolated to other clinical settings. Comparison of our results with those of other recent studies (7)(8)(9)(10)(11)(12)(13)(14) suggests that diagnostic accuracy can strongly depend on patient selection and on the cardiac natriuretic peptide assayed (BNP, N-terminal pro-A-type natriuretic peptide, or NT-proBNP), as well as on the analytical performance and diagnostic accuracy of the immunoassay chosen.
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