凝血过程分为血管内与血管外两个系统。一期凝血酶原时间是检查血管外凝血过程的,须有标准化的组织凝血活酶试剂。在此反应中,组织凝血活酶代替了血小板的凝血因子以及凝血因子Ⅷ和Ⅸ。因此,患血小板减少症、血友病甲或乙时,检查凝血酶原时间是正常的。因子Ⅶ作为组织凝血活酶的辅助因子在血管外凝 Blood clotting process is divided into two systems of intravascular and extravascular. A prothrombin time is to examine the extravascular coagulation process, there must be a standardized tissue thromboplastin reagent. In this reaction, tissue thromboplastins replace platelet-derived coagulation factors and coagulation factors VIII and IX. Therefore, with thrombocytopenia, hemophilia A or B, check prothrombin time is normal. Factor Ⅶ coagulation as a cofactor of coagulation in extravascular coagulation