FIND, Foundation for Innovative New Diagnostics, Kampala, Uganda.
BMC Infect Dis. 2011 May 13;11:125. doi: 10.1186/1471-2334-11-125.
Direct sputum smear microscopy is the mainstay of TB diagnosis in most low and middle income countries, and is highly specific for Mycobacterium tuberculosis in such settings. However it is limited by low sensitivity, particularly in HIV co-infected patients. Concentration by centrifugation has been reported to be more sensitive than direct smear preparation, but is only suitable for referral laboratories. Simpler concentration methods that could be applied in peripheral laboratories are urgently needed.
We evaluated the feasibility of an early prototype ligand-coated magnetic bead technology to concentrate M. tuberculosis prior to detection by LED-based fluorescence microscopy compared with direct Ziehl-Neelsen microscopy and direct and concentrated fluorescence microscopy in a reference laboratory in Kampala, Uganda. Results were compared with MGIT 960 liquid culture and Lowenstein-Jensen culture.
Compared to culture, concentrated FM had significantly higher sensitivity than direct ZN (74.8% and 51.4%), magnetic bead-FM (65.4%) and direct FM (58.9%). The sensitivity of magnetic bead FM was significantly higher than direct ZN (p<0.001) but not significantly higher than direct FM (p=0.210). The specificity of magnetic bead FM and concentrated FM was significantly lower than direct ZN (88.6%, 94.3% and 98.9% respectively) and direct FM (99.4%). There was no significant difference in specificity between magnetic bead FM and concentrated FM. Allowing for blinded resolution of discrepant results, the specificity of magnetic bead FM increased to 93.1%. Direct microscopy was simpler than concentrated FM and Magnetic bead FM which both had a similar number of steps.
The sensitivity of the early prototype magnetic bead FM was lower than concentrated FM, similar to direct FM, and significantly higher than direct ZN. Both magnetic bead and concentration by centrifugation led to reduced specificity compared with the direct smear methods. Some magnetic bead FM false positive results were not easily explained and should be further investigated. The prototype version of the magnetic bead procedure tested here was of similar complexity to concentration by centrifugation. As such, if the sensitivity of the magnetic bead FM could be improved in future versions of the technology, this may offer a viable alternative to centrifugation.
直接痰涂片显微镜检查是大多数中低收入国家结核病诊断的主要方法，在这些环境下对结核分枝杆菌具有高度特异性。然而，它的灵敏度有限，特别是在 HIV 合并感染患者中。离心浓缩已被报道比直接涂片准备更敏感，但仅适用于转诊实验室。迫切需要更简单的可在周边实验室应用的浓缩方法。
我们评估了一种早期的配体涂层磁珠技术，用于在乌干达坎帕拉的参考实验室中，通过基于 LED 的荧光显微镜检测之前浓缩结核分枝杆菌，与直接 Ziehl-Neelsen 显微镜检查和直接及浓缩荧光显微镜检查进行比较。结果与 MGIT 960 液体培养和 Lowenstein-Jensen 培养进行了比较。
与培养相比，浓缩 FM 比直接 ZN（74.8%和 51.4%）、磁珠-FM（65.4%）和直接 FM（58.9%）具有更高的灵敏度。磁珠 FM 的灵敏度明显高于直接 ZN（p<0.001），但与直接 FM 无显著差异（p=0.210）。磁珠 FM 和浓缩 FM 的特异性明显低于直接 ZN（分别为 88.6%、94.3%和 98.9%）和直接 FM（99.4%）。磁珠 FM 和浓缩 FM 之间的特异性无显著差异。考虑到对差异结果进行盲法解析，磁珠 FM 的特异性提高至 93.1%。直接显微镜检查比浓缩 FM 和磁珠 FM 都更简单，而后者的步骤数相似。
早期原型磁珠 FM 的灵敏度低于浓缩 FM，与直接 FM 相似，明显高于直接 ZN。与直接涂片法相比，磁珠和离心浓缩均导致特异性降低。一些磁珠 FM 假阳性结果不易解释，应进一步研究。这里测试的磁珠程序的原型版本与离心浓缩的复杂性相似。因此，如果磁珠 FM 的灵敏度能够在该技术的未来版本中得到提高，那么这可能是离心的一种可行替代方法。
