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Persons using assistive technology might not be able to fully access information in this file. For assistance, please send e-mail to: mmwrq@cdc.gov. Type 508 Accommodation and the title of the report in the subject line of e-mail. Notice to Readers: Update: Nucleic Acid Amplification Tests for TuberculosisOn September 30, 1999, the Food and Drug Administration approved a reformulated Amplified Mycobacterium Tuberculosis Direct Test* (MTD) (Gen-Probe®, San Diego, California) for detection of Mycobacterium tuberculosis in acid-fast bacilli (AFB) smear-positive and smear-negative respiratory specimens from patients suspected of having tuberculosis (TB). MTD and one other nucleic acid amplification (NAA) test, the Amplicor® Mycobacterium Tuberculosis Test (Amplicor) (Roche® Diagnostic Systems, Inc., Branchburg, New Jersey), previously had been approved for the direct detection of M. tuberculosis in respiratory specimens that have positive AFB smears. This notice updates the original summary published in 1996 (1) and provides suggestions for using and interpreting NAA test results for managing patients suspected of having TB. The appropriate number of specimens to test with NAA will vary depending on the clinical situation, the prevalence of TB, the prevalence of nontuberculous mycobacteria (NTM), and laboratory proficiency (2,3). Based on available information, the following algorithm is a reasonable approach to NAA testing of respiratory specimens from patients with signs or symptoms of active pulmonary TB for whom a presumed diagnosis has not been established. Algorithm
NAA tests can enhance diagnostic certainty, but they do not replace AFB smear or mycobacterial culture, and they do not replace clinical judgement. Clinicians should interpret these tests based on the clinical situation, and laboratories should perform NAA testing only at the request of the physician and only on selected specimens. Laboratorians should not reserve material from clinical specimens for NAA testing if this compromises the ability to perform the other established tests that have better-defined diagnostic utility and implications. Specificity of NAA tests varies between laboratories as a result of unrecognized procedural differences and differences in cross-contamination rates (4). Multiple specimens from the same patient should not be tested together to reduce risks of methodologic errors. Laboratory directors should provide to clinicians information on the performance of NAA tests in the local setting, including sensitivity and specificity compared with culture for both smear-positive and smear-negative respiratory specimens. Substantial discrepancies can indicate problems with either culture or NAA technique. The number of NAA tests repeated because of failure of negative and positive controls also should be reported. Clinicians should understand the impact that changes in sensitivity, specificity, prevalence of TB, and prevalence of other mycobacterial diseases can have on the predictive value of the NAA test. Information is limited regarding NAA test performance for nonrespiratory specimens, or specimens from treated patients. NAA tests often remain positive after cultures become negative during therapy and can remain positive even after completion of therapy. References
* Use of trade names and commercial sources is for identification only and does not constitute endorsement by CDC or the U.S. Department of Health and Human Services. Amplicor is not approved for use with smear-negative samples. . Disclaimer All MMWR HTML versions of articles are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the electronic PDF version and/or the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices. **Questions or messages regarding errors in formatting should be addressed to mmwrq@cdc.gov.Page converted: 7/6/2000 |
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