Report of an Expert Consultation on the Uses of Nucleic Acid Amplification Tests for the Diagnosis of Tuberculosis
Guidelines for the use of nucleic acid amplification (NAA) tests for the diagnosis of tuberculosis (TB) were published in 1996 (1) and updated in 2000 (2). Since then, NAA testing has become a routine procedure in many institutions for the diagnosis of TB, because NAA tests can rapidly and reliably detectMycobacterium tuberculosis bacteria directly in a specimen one or more weeks earlier than culture. Earlier laboratory confirmation of TB can lead to earlier treatment initiation, better patient care and outcomes, greater opportunities to interrupt transmission, and improved public health interventions.
Two NAA tests are approved for use in the United States by the Food and Drug Administration (FDA). The Enhanced Amplified Mycobacterium Tuberculosis Direct Test (E-MTD, Gen-Probe, San Diego, California) is approved for detection of M. tuberculosis complex bacteria in acid-fast bacilli (AFB) smear-positive and smear-negative respiratory specimens from patients suspected of having TB. The E-MTD test combines isothermal transcription-mediated amplification of a portion of the 16S rRNA with a detection method that uses a hybridization probe specific for M. tuberculosis complex bacteria. The MTD test displays a sensitivity of >95% for detecting M. tuberculosis bacteria in respiratory specimens from AFB-smear positive TB suspects and 75% to 90% for detecting M. tuberculosis bacteria in respiratory specimens from AFB-smear negative TB suspects. The Amplicor Mycobacterium tuberculosis Test (Amplicor, Roche Diagnostics) is approved for the detection of M. tuberculosis complex bacteria in AFB smear-positive respiratory specimens from patients suspected of having TB. This test uses the polymerase chain reaction (PCR) to amplify a portion of the 16S rRNA gene that contains a sequence that hybridizes with an oligonucleotide probe specific for M. tuberculosis complex bacteria. The Amplicor test displays a sensitivity of >95% for detecting M. tuberculosis bacteria in respiratory specimens from AFB-smear positive TB suspects and a sensitivity of 60% to 70% for detecting M. tuberculosis bacteria in respiratory specimens from AFB-smear negative TB suspects.
In response to a request from the Advisory Council for the Elimination of Tuberculosis (ACET), the Association of Public Health Laboratories (APHL) and CDC convened an expert panel to evaluate the evidence and propose new guidelines for the use of NAA tests for the diagnosis of TB in the United States. The panel included TB clinicians; TB control officials; laboratory directors or supervisors from small, medium and large public health laboratories, hospital laboratories, and commercial laboratories; and representatives from the Regional Training and Medical Consultation Centers, APHL, and CDC. Meeting on June 13, 2008, the panel reviewed available publications and guidelines to discuss applications of NAA testing for TB diagnosis and control and to propose recommendations.