Evaluation of Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test and PCR for direct detection of Mycobacterium tuberculosis in clinical specimens

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Abstract
The Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test (AMTD) is a direct specimen assay for the identification of Mycobacterium tuberculosis from respiratory samples. rRNA is amplified, and the product is detected with a specific chemiluminescent probe. We performed a retrospective evaluation of three separate respiratory specimens from each of 250 patients by using the AMTD and compared the results with those of microscopy, culturing, and a patient chart review. From the latter results, 198 patients (594 specimens) were found negative for M. tuberculosis by culturing and clinical criteria. The overall specificity of the AMTD after discrepancy resolution was 98.5% (585 of 594). There were 52 patients with culture-proven and/or clinically diagnosed tuberculosis. Of these 156 specimens, the organism was cultured from 142 (91%), and acid-fast microscopy was positive for 105 (67.3%). The AMTD was positive for 142 (91%) specimens from these patients. Tuberculosis patient samples were tested by a PCR assay which uses primers for amplification of the IS6110 insertion sequence of the M. tuberculosis complex. The PCR assay detected 144 of the 156 (92.3%) specimens. Overall, when three specimens per patient were examined, the AMTD found all 52 patients positive for tuberculosis, while the PCR assay found 51 patients positive by agarose gel analysis and all 52 patients positive by Southern blot hybridization.