A novel genetic tuberculosis screen can reduce the time period needed for conclusive diagnosis, researchers in the United States report. Cathal E. O'Sullivan and colleagues at the National Cancer Institute in Bethesda, Md., and the Mayo Clinic and Foundation in Rochester, Minn., evaluated the Amplified Mycobacterium Tuberculosis Direct (AMTD) test from San Diego-based Gen-Probe Inc.

The TB screen was both highly accurate and significantly faster than conventional diagnostic techniques, O'Sullivan and coauthors found. The researchers assessed the AMTD assay's ability to detect TB genetic material in more than 550 clinical samples from patients with suspected TB. The overall sensitivity and specificity of the AMTD test was 91.2 percent and 98.9 percent respectively, compared with the combined results of clinical and culture-based TB tests, they said.

Moreover, the positive and negative predictive values of AMTD test results were 91.7 percent to 99.7 percent for both respiratory and nonrespiratory specimens, study data showed. AMTD assay inhibitors were seen in just over 3 percent of the test samples.

On average, using the AMTD screen for diagnosis saved almost nine days of waiting for test results ("Evaluation of Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test by Using Respiratory and Nonrespiratory Specimens in a Tertiary Care Center Laboratory," Journal of Clinical Microbiology, 2002;40(5):1723-1727).

"The assay, used in a general mycobacteriology laboratory setting, represents an important advance in improving the speed and accuracy of diagnosis in the management of patients with tuberculosis," O'Sullivan and colleagues concluded.

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