Coll P, Garrigó M, Moreno C, Martí N
Hospital de Sant Pau, Servei de Microbiologia, Barcelona, Spain.
Int J Tuberc Lung Dis. 2003 Sep;7(9):886-91.
Nucleic acid amplification tests, such as the Amplified Mycobacterium Tuberculosis Direct (MTD) Test, may improve early diagnosis of tuberculosis when used in combination with acid-fast bacilli smear examination with a similar turnaround time.
To evaluate the routine use of MTD in respiratory and non-respiratory samples; to investigate the improvement of MTD specificity and positive predictive value by defining an equivocal zone for result interpretation.
MTD was performed according to the instructions supplied by the manufacturer. An equivocal zone was included for interpretation of results. Discordant results with culture were resolved by incorporating clinical data and multiple specimen analysis.
The overall sensitivities, specificities, and positive and negative predictive values for respiratory specimens (n = 3308) were 90.8, 99.9, 99.1, and 99.2%, respectively. With extra-pulmonary specimens (n = 1350) those values were 67.4, 99.9, 98.2, and 97.9%, respectively. By implementing an equivocal zone, the specificity and positive predictive value of MTD were improved (from 99.1% and 88.6% to 99.9% and 98.9% respectively) without significantly altering other performance characteristics.
Amplification assays cannot yet replace the conventional diagnostic techniques. Nevertheless, MTD is a reliable method for the direct detection of M. tuberculosis in clinical specimens. The number of false-positive results can be limited by defining an equivocal zone.
核酸扩增检测，如结核分枝杆菌直接扩增检测（MTD），与抗酸杆菌涂片检查联合使用且周转时间相似时，可能会改善结核病的早期诊断。
评估MTD在呼吸道和非呼吸道样本中的常规应用；通过定义结果解释的可疑区域来研究MTD特异性和阳性预测值的改善情况。
根据制造商提供的说明进行MTD检测。结果解释纳入可疑区域。通过纳入临床数据和多样本分析解决与培养结果不一致的情况。
呼吸道样本（n = 3308）的总体敏感性、特异性、阳性和阴性预测值分别为90.8%、99.9%、99.1%和99.2%。肺外样本（n = 1350）的这些值分别为67.4%、99.9%、98.2%和97.9%。通过设置可疑区域，MTD的特异性和阳性预测值得到了提高（分别从99.1%和88.6%提高到99.9%和98.9%），而其他性能特征没有显著改变。
扩增检测尚不能取代传统诊断技术。然而，MTD是临床样本中直接检测结核分枝杆菌的可靠方法。通过定义可疑区域可以限制假阳性结果的数量。
