美国最新的HIV诊断实验室测试，英国性健康协会窗口期，WHO窗口期

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HIV感染后，HIV-1的RNA（核糖核酸）立即断断续续地出现，但血浆中没有病毒标识物可以持续检测到。在感染近似10天后，血浆中的HIV-1的RNA可以通过NAT（核酸测试）检测出，并且数量上升到很高的水平。接着，p24抗原开始表达，在RNA最初检测后的4到10天内，通过4代免疫测定检测出。然而，p24抗原免疫测定是短暂的，因为当抗体开始发展后，抗体与p24抗原结合，形成免疫复合物。该免疫复合物妨碍p24化验检测，除非化验包括分解抗原-抗体复合物的步骤。接着免疫球蛋白IGM抗体表达，可以在p24最初可检测到的3至5天后，通过3代和4代免疫测定检测出，即在RNA出现的10至13天后。最后，IGG抗体出现并在HIV感染的整个过程中持续存在。第一和第二代免疫测定设计为仅检测IGG抗体，其在感染早期，在敏感性方面展示相当大的易变性，第一和第二代免疫测定在RNA最初的测定后的18至38天或更长时间变得有反应性。
（从上面的图中和描述中可以看到，各试剂可以检测到的日期：
RNA: 感染后10天，核酸测试
P24: 感染后14～20天，四代试剂
IGM抗体：感染后20～25天，三代和四代试剂
IGG抗体：28～48天，第一和第二代试剂）

下面是英国性健康对窗口期的看法：
HIV testing using the latest (fourth generation) tests is recommended in the BHIVA / BASHH / BIS UK guidelines for HIV testing (2008). These assays test for HIV antibodies and p24 antigen simultaneously. A fourth generation HIV test on a venous blood sample performed in a laboratory will detect the great majority of individuals who have been infected with HIV at 4 weeks after specific exposure.
Patients attending for HIV testing who identify a specific risk occurring less than 4 weeks previously should not be made to wait before HIV testing as doing so may miss an opportunity to diagnose HIV infection (and in particular acute HIV infection during which a person is highly infectious). They should be offered a fourth generation laboratory HIV test and be advised to repeat it when 4 weeks have elapsed from the time of the last exposure.
A negative result on a fourth generation test performed at 4 weeks post-exposure is highly likely to exclude HIV infection. A further test at 8 weeks post-exposure need only be considered following an event assessed as carrying a high risk of infection.
四代四周绝大部分排除了。八周后复测仅仅为了高度感染事件的评估。

世界卫生组织WHO：
Most individuals develop antibodies to HIV-1/2 within 28 days and therefore antibodies may not be detectable early after infection, the so-called window period. This early period of infection represents the time of greatest infectivity; however HIV transmission can occur during all stages of the infection.
大部分人在28天内出现抗体。