Assessment of Laboratory Performance of Nucleic Acid Amplification Tests for Detection of Mycobacterium tuberculosis

Abstract

During implementation of the Centers for Disease Control and Prevention's Mycobacterium tuberculosisnucleic acid amplification (NAA) evaluation program, 27.1% of participants used the same biological safety cabinet for NAA and specimen processing; 28.8% reported not using unidirectional workflow. An association between false positives and adverse responses to quality assurance questions (P ‫؍‬ 0.04) illustrated the need for following NCCLS recommendations.Procedures for rapid laboratory testing for diagnosing tuberculosis (TB) are a major component of public health policy for controlling TB in the United States (17). The nucleic acid amplification (NAA) test for direct detection of Mycobacterium tuberculosis in patient-derived specimens provides a rapid result to determine whether a patient has TB. Information from the M. tuberculosis NAA result may contribute to patient diagnosis and to decisions involving respiratory isolation within a hospital. Two M. tuberculosis NAA tests, Gen-Probe MTD and the Roche Amplicor MTB, were approved by the U.S. Food and Drug Administration in 1995 for use with acid-fast bacilli smear-positive respiratory specimens (3). In 2000, the modified Gen-Probe MTD test was approved for use with smear-negative respiratory specimens (4). The U.S. Department of Health and Human Services has advocated increased use of M. tuberculosis NAA tests for rapid diagnosis and control of TB in the Healthy People 2010 Objectives (18).Commercial development of the Gen-Probe MTD and the Roche Amplicor MTB provides access to M. tuberculosis NAA tests for routine diagnostic testing in laboratories which may not have had experience with molecular testing. The NAA tests, however, require specific quality assurance (QA) practices to prevent contamination. While the performance characteristics of M. tuberculosis NAA tests were documented previously (1, 2, 6-11, 15, 16), there is little knowledge of laboratory practices and performance associated with these tests in routine diagnostic settings (13,14).To assess laboratory practices and performance with M. tuberculosis NAA tests, the Centers for Disease Control and Prevention (CDC) implemented a M. tuberculosis NAA testing performance evaluation program in 1997. This voluntary program uses samples containing M. tuberculosis and nontuberculous mycobacteria (NTM), providing an anonymous challenge for laboratories (http://www.phppo.cdc.gov/mpep/mtbnaa.asp). An aggregate report of results is provided to participants with analyses of common problems. We describe here the laboratory participants, laboratory practices for QA reported, aggregate testing performance, and analyses of the association between performance and QA practices for the combined results from two 1997 shipments.Test samples were developed from patient-derived isolates of M. tuberculosis and NTM (Mycobacterium kansasii and Mycobacterium gordonae). Stock suspensions were prepared from 8-day growth on Lowenstein-Jensen medium and adjusted to an absorbency of 0.2 at 420 nm. Dilutions were made in either ...

Performance of Nucleic Acid Amplification Tests in Patients with Presumptive Pulmonary Tuberculosis in Taiwan

“…Taken together, these findings suggest that it may be beneficial to replace in-house PCR with other NAA platforms in clinical practice. Of note, Xpert may report false-positive results for five NTM species ( M. abscessus , M. marinum , M. smegmatis , M. phlei and M. aurum ) [ 26 , 27 ].…”

roles of laboratories and laboratory systems in effective tuberculosis control

“…25 However, further improvements in the sensitivity, cost and robustness of NAAT must be achieved before it can be generally adopted by most laboratories. 26 For example, cross-contamination of cultures can easily lead to false positives. 27,28 Also, DST and NAAT require training, EQA and standard practices to achieve the levels of accuracy required to establish credibility and to justify the resources needed to further expand services.…”