Journal of clinical microbiology
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J. Clin. Microbiol. · Jan 1999
False-positive Gen-Probe direct Mycobacterium tuberculosis amplification test results for patients with pulmonary M. kansasii and M. avium infections.
The Gen-Probe Amplified Mycobacterium Tuberculosis Direct (MTD) test has been approved for use in the United States for the rapid diagnosis of pulmonary tuberculosis in patients with acid-fast smear-positive sputum samples since 1996. Four patients infected with human immunodeficiency virus and one chronic pulmonary-disease patient seen in our institutions with abnormal chest radiographs and fluorochrome stain-positive sputa were evaluated for tuberculosis, including performance of the MTD test on expectorated sputum samples. Three of these five patients' sputa were highly smear-positive (i.e. , more than 100 bacilli per high-power field), while two patient's sputa contained 1 to 10 bacilli per field. ⋯ These findings indicate that low-level false-positive MTD results can occur due to the presence of M. kansasii, M. avium, and possibly other Mycobacterium species other than M. tuberculosis in sputum. Low-level positive MTD results of 30,000 to 500,000 RLU should be interpreted in light of these findings. It remains to be determined if the enhanced MTD test (MTD 2) recently released by Gen-Probe will provide greater specificity than that observed in this report with its first-generation test.