Comparison of enhanced Mycobacterium tuberculosis amplified direct test with COBAS AMPLICOR Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis complex in respiratory and extrapulmonary specimens

The new Roche COBAS AMPLICOR Mycobacterium tuberculosis Assay was compared to the Gen-Probe enhanced Mycobacterium tuberculosis Amplified Direct Test (AMTDII). A total of 486 specimens (296 respiratory and 190 extrapulmonary) collected from 323 patients were tested in parallel with both assays. Resu lts were compared with those of acid-fast staining and culture, setting the combination of culture and clinical diagnosis as the "gold standard." Afte r resolution of discrepant results, the sensitivity, specificity, and posit ive and negative predictive values for AMTDII were 85.7, 100, 100, and 90.4 % for respiratory specimens and 82.9, 100, 100, and 95.5% for extrapulmonar y specimens, respectively. The corresponding values for AMPLICOR were 94.2, 100, 100, and 96.6% for respiratory specimens and 85, 100, 100, and 96.1% for extrapulmonary specimens, respectively. No significant differences were observed between the results of both assays or, within each one? between r espiratory and extrapulmonary specimens. The difference between AMTDII and AMPLICOR sensitivities was related to the presence of inhibitory samples, w hich the former assay, lacking an internal amplification control (IAC), cou ld not detect. The overall inhibition rate for the AMPLICOR assay was 3.9% (19 specimens). It is concluded that, although both amplification assays pr oved to be rapid and specific for the detection of M. tuberculosis complex in clinical samples, AMPLICOR, by a completely automated amplification and detection procedure, was shown to be particularly feasible for a routine la boratory setting. Finally, AMTDII is potentially an excellent diagnostic te chnique for both respiratory and extrapulmonary specimens, provided that an IAC is included with the assay.