Evaluation of two commercial amplification assays for detection of Mycobacterium tuberculosis complex in respiratory specimens.

To evaluate the usefulness of two standardized commercially available amplification assays for the detection of Mycobacterium tuberculosis: Amplicor test (Roche) and MTD-Amplified direct test (Gen-Probe) a total of 281 respiratory specimens from 198 patients with symptoms of pulmonary diseases were examined and compared with conventional methods. Fifty-seven specimens were positive and 218 negative by both amplification assays. Three specimens were reactive by Amplicor only, and three by MTD only. In comparison with culture, the sensitivity, specificity, positive predictive value and negative predictive value were 96.0, 94.8, 80.0, and 99.1%, respectively, for the Amplicor test; the corresponding values were 94.0, 94.4, 78.3, and 98.6%, respectively, for the MTD. However, when 28 specimens from 14 patients on antituberculous therapy were excluded the improvement in PPV and specificity of both assays was obtained. In conclusion, both commercially available amplification tests are almost equally sensitive and specific and are suitable for the implementation in daily routine work in the specialized clinical laboratories.