Comparative evaluation of two commercial amplification assays for direct detection of Mycobacterium tuberculosis complex in respiratory specimens

Abstract

Two commercial assays detecting the presence of Mycobacterium tuberculosis complex in clinical specimens by rRNA target amplification (Gen-Probe Amplified M. tuberculosis Direct Test [AMTD]) and PCR (Amplicor) were evaluated. The tests were applied to 327 digested, decontaminated respiratory specimens collected from 236 patients. Results were compared with those of acid-fast staining and culture. The combination of culture and clinical diagnosis was considered the "gold standard." A total of 60 specimens were collected from 27 patients with a diagnosis of pulmonary tuberculosis. Thirteen of these specimens were from patients receiving standard antituberculosis therapy and therefore were not included in the comparison. Of the remaining 47 specimens, 33 were smear positive, 40 were culture positive, 45 were AMTD positive, and 39 were Amplicor positive. After resolution of discrepant results, the overall sensitivities, specificities, and positive and negative predictive values were 77, 100, 100, and 95 for staining; 87, 100, 100, and 97.4 for culture; 95.9, 98.9, 94, and 99.2 for AMTD; and 85.4, 99.6, 97.9, and 97.1 for Amplicor, respectively. Agreement between AMTD and Amplicor assay results was 96.8%. It is concluded that although both nucleic acid amplification methods are rapid and specific for the detection of M. tuberculosis complex in respiratory specimens, AMTD appeared to be more sensitive than Amplicor.

Evaluation of a commercial ligase chain reaction kit (Abbott LCx) for direct detection of Mycobacterium tuberculosis in pulmonary and extrapulmonary specimens

“…Our data appear comparable to those reported for other commercially available amplification systems. Our overall resolved sensitivity of 95.53% is within the range (91.0 to 98.4%) reported for the Gen-Probe assay (1,9,14,15,19) and better than the 67.6 to 86.0% reported for the Amplicor Direct test (4-6, 10, 17).…”

“…Among true-positive LCx results, most samples came from tuberculous patients under treatment. Such an occurrence is well documented both for DNA-and RNA-based amplification systems (2,10,11,15); the long-lasting detectability of nucleic acids after the culture becomes negative makes LCx unsuitable for the monitoring of therapeutic efficacy.…”

Evaluation of the semiautomated Abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis in respiratory specimens

“…In a further study (30), AMTDT was evaluated with 1,117 specimens from 988 patients, with a positivity rate of 12% and a staining sensitivity of 40%; the sensitivities values obtained with smear-positive and smear-negative specimens (100 and 81%, respectively) were higher than those reported in our study. A comparative evaluation between AMTDT and the Amplicor test was recently carried out with 327 specimens from 236 patients (31). With a prevalence of 15%, the sensitivities, specificities, PPVs, and NPVs were 95.9, 98.9, 94 and 99.2%, respectively, for AMTDT and 85.4, 99.6, 97.9 and 97.1%, respectively, for the Amplicor test.…”

PCR-based diagnostics for infectious diseases: uses, limitations, and future applications in acute-care settings

“…One of the earliest recognised applications of PCR for clinical practice was for detection of Mycobacterium tuberculosis. 54,55 Disease characteristics favouring the development of a non-culture-based test for tuberculosis included week-long to month-long delays associated with standard testing, and the public-health imperative associated with early recognition, isolation, and treatment of infected patients. Two PCR-based assays are approved by the FDA for direct detection of M tuberculosis from clinical specimens (table 1).…”