Woods G L
Department of Pathology, University of Texas Medical Branch, Galveston 77555-0740, USA.
Arch Pathol Lab Med. 1999 Nov;123(11):1002-6. doi: 10.5858/1999-123-1002-MMITDA.
Nucleic acid amplification (NAA) tests for direct detection of Mycobacterium tuberculosis complex in respiratory specimens have the potential to provide a more rapid diagnosis of pulmonary tuberculosis (TB) than is currently possible by conventional stain, culture, and identification tests. Currently, 2 NAA tests-enhanced Amplified Mycobacterium Tuberculosis Direct (MTD) Test (Gen-Probe, Inc) and Amplicor Mycobacterium tuberculosis Test (Roche Molecular Systems, Inc)-have been approved by the Food and Drug Administration for testing respiratory specimens that are smear positive for acid-fast bacilli (AFB). This restriction to AFB smear-positive specimens was based on data from the initial clinical trials conducted to evaluate these products that showed low sensitivity (ie, 48%-53%) and less-than-optimal specificity (ie, 96%-99%) in AFB smear-negative specimens. Data from the clinical trial for the enhanced MTD test and from 2 subsequent studies, however, suggest that this version of the MTD test is a reliable tool for rapid diagnosis of pulmonary TB, regardless of the AFB smear result. Both NAA tests have been evaluated for diagnosis of extrapulmonary TB, and results were comparable to the results of tests performed with respiratory specimens. The NAA tests also appear to be reliable for rapid identification of M tuberculosis complex in positive broth cultures of all specimen types except blood. The impact of the NAA tests on patient outcome varies based on the AFB smear result. With smear-positive results, public health and hospital infection control resources are predominantly affected. With smear-negative results, however, the potential for affecting patient outcome is much greater. In patients with smear-negative results, the NAA test can result in earlier diagnosis of TB and subsequent initiation of therapy. Use of these tests also may eliminate the need for invasive diagnostic procedures, which are costly and pose an added risk to the patient, and they may allow earlier discharge of hospitalized patients.
用于直接检测呼吸道标本中结核分枝杆菌复合群的核酸扩增（NAA）试验，有可能比目前通过传统染色、培养和鉴定试验更快速地诊断肺结核（TB）。目前，两种NAA试验——增强型结核分枝杆菌直接扩增（MTD）试验（Gen-Probe公司）和Amplicor结核分枝杆菌试验（罗氏分子系统公司）——已获得美国食品药品监督管理局批准，用于检测抗酸杆菌（AFB）涂片阳性的呼吸道标本。对AFB涂片阳性标本的这种限制是基于评估这些产品的初始临床试验数据，这些数据显示在AFB涂片阴性标本中敏感性较低（即48%-53%）且特异性不够理想（即96%-99%）。然而，增强型MTD试验的临床试验数据以及随后的两项研究表明，无论AFB涂片结果如何，这种版本的MTD试验都是快速诊断肺结核可靠工具。两种NAA试验均已用于肺外结核诊断评估，结果与呼吸道标本检测结果相当。除血液外，NAA试验在所有标本类型的阳性肉汤培养物中快速鉴定结核分枝杆菌复合群方面似乎也很可靠。NAA试验对患者预后的影响因AFB涂片结果而异。涂片结果为阳性时，主要影响公共卫生和医院感染控制资源。然而，涂片结果为阴性时，影响患者预后的可能性要大得多。对于涂片结果为阴性的患者，NAA试验可导致更早诊断结核病并随后开始治疗。使用这些试验还可能无需进行侵入性诊断程序，这些程序成本高昂且会给患者带来额外风险，并且可能使住院患者更早出院。
