Is it appropriate to routinely use a nucleic acid amplification test for the diagnosis of tuberculosis?

The purpose of this study was to compare the usefulness of the nucleic acid amplification (NAA) test against conventional tests under normal laboratory operational conditions. The NAA test was performed on the first sputum specimen of all patients. Liquid media culture, solid media culture, and Ziehl–Neelsen stain for an acid-fast bacilli (AFB) smear were performed on three sputum specimens. The results were calculated using the gold standard of either the culture results or the clinical diagnosis. Of the 593 patients tested, 151 (25.5%) were diagnosed with pulmonary tuberculosis. The sensitivity of the first specimen only was 64% for the NAA test, 54% for the AFB smear, 77% for BACTEC MGIT 960 culture, 40% for Lowestain-Jensen (LJ) culture, and 25% for 7H11 culture. The sensitivity when using all three specimens increased to 63% for AFB smear, 87% for BACTEC MGIT 960 culture, 51% for LJ culture, and 40% for 7H11 culture. The specificity was 100% for all culture tests, 99% for the AFB smear, and 99.5% for NAA test. The mean turnaround time was 1.34 days for NAA, 0.59 days for AFB smear, 11 days for BACTEC MGIT 960 culture, 23 days for LJ culture, and 20 days for 7H11 culture. We conclude that the sensitivity of NAA is still far from ideal, and the test is not cost effective. Thus, the COBAS AMPLICOR PCR system is not suitable for routine use in microbiology laboratories.

摘要本研究是比較在實驗室正常運行條件下進行核酸擴增技術(Nucleic acid amplification，NAA)與傳統培養方法對於結核病診斷的評估。 NAA 的測試只做在所有病人的第一套痰檢體。液體培養基（BACTEC MGIT 960），固體培養基(Lowenstein-Jensen，LJ與7H11)與抗酸染色塗片則進行了3套痰檢體。診斷為肺結核的黃金標準是指培養結果或臨床診斷。在593病人中，151（25.5％）診斷為肺結核。在NAA檢測方法中第一套檢體的靈敏度(sensitivity)為64％，抗酸染色塗片為54％， BACTEC MGIT 960為77％， LJ 為40％和7H11為 25％。在所有三套檢體中靈敏度則提高為抗酸染色塗片為63％、BACTEC MGIT 960 為87％、LJ為51％和7H11為40％。特異性(specificity)在所有的培養方法為 100％、抗酸染色塗片為99％和 NAA 為99.5％。平均迴轉時間（TAT）NAA為 1.34天，抗酸染色塗片為0.59天， BACTE MGIT 960為11天、LJ為23天、7H11為20天。我們的結論是NAA的敏感度遠遠不夠理想，也不符合成本效益。因此 COBAS AMPLICOR PCR是不適合常規實驗室使用。