Comparison of real-time polymerase chain reaction using the Smart Cycler and the Gen-Probe amplified Mycobacterium tuberculosis direct test for detection of M. tuberculosis complex in clinical specimens.

The performance of a real-time polymerase chain reaction (PCR) assay using the Smart Cycler instrument and a minor groove binding MGB Eclipse probe (Epoch Biosciences, Bothell, WA) for identification of Mycobacterium tuberculosis complex in acid-fast bacillus smear-positive and smear-negative clinical specimens was assessed by comparing results to the Amplified M. tuberculosis Direct Test (MTD) and mycobacterial culture plus clinical diagnosis. After initial testing, the overall sensitivity, specificity, and positive and negative predictive values of PCR for the 172 specimens submitted for mycobacterial culture were 86.3%, 100%, 100%, and 94.5%, respectively. These same values for MTD were 98.0%, 99.2%, 98.0%, and 99.2%. For 83 additional specimens, only MTD and PCR were performed; 5 specimens were positive and 78 were negative by both tests. The sensitivity of the PCR assay was improved by using different primers and probes. The time to a result for real-time PCR, starting with a decontaminated sample, was less than 3 h compared with 5-6 h for the MTD.