Activated clotting time 激活全血凝固时间（也称活化凝血时间）
首先，ACT，是相对于凝血时间clotting time（CT）来说的。
◆CT指离体的全血置入试管后，凝血因子Ⅻ被异物表面（如玻璃）激活，启动内源性凝血，血液发生凝固所需的时间。
◆ACT是指在待检全血中加入白陶土部分凝血活酶悬液（人为加入激活剂），充分激活F Ⅻ、F Ⅺ，启动内源性凝血途径引发血液凝固所需要的时间。
可见ACT也是走的内源性途径这一派系的，那么ACT与APTT有什么区别呢？
◆ACT加入的是全血，血液中含有内源性凝血所需要的全部凝血因子、血小板及钙离子。
◆APTT加入的是血浆，无血小板，其结果不能反应血小板的情况。
Activated clotting time (ACT), also known as activated coagulation time is a test of coagulation.
The ACT test can be used to monitor anticoagulation effects, such as high-dose heparin before, during, and shortly after procedures that require intense anticoagulant administration, such as cardiac bypass, cardiac angioplasty, thrombolysis, extra-corporeal membrane oxygenation (ECMO) and continuous dialysis. It measures the seconds needed for whole blood to clot upon exposure to an activator of an intrinsic pathway by the addition of factor XII activators. The clotting time is based on a relative scale and requires a baseline value（需要一个基线值） for a point of comparison due to inconsistencies between the source and formulation of the activator being used. It is usually ordered in situations where the partial thromboplastin time (PTT) test may take an excessive amount of time to process or is not clinically useful. Prolongation of the ACT may indicate a deficiency in coagulation factors, thrombocytopenia or platelet dysfunction.
为什么大剂量应用肝素时就不用APTT监测了呢？
