FV is a cofactor that can enhance the activity of FXa 350,000 times after forming a complex with calcium ions and phospholipids. 2. Clinical manifestations Only pure congeners have bleeding manifestations, mostly caused by trauma. Spontaneous bleeding is rare, as mucosal and subcutaneous bleeding, and excessive menstruation in women. Hematuria and joint cavity bleeding are rare. Heterozygotes usually have no bleeding symptoms, and the bleeding symptoms of pure congeners can be mild and are not related to the plasma FV level. The prolonged clotting time of pure congeners, mainly prolonged prothrombin time (PT), can be corrected by normal adsorbed plasma. Partial thromboplastin time (PPT) is prolonged. Plasma factor V (V:C) activity is measured to be decreased. 4. Treatment overview When there is active bleeding, transfusion of normal fresh frozen plasma or whole blood or cold precipitate for treatment, the biological half-life of FV is about 12~36h, but there is no definite conclusion as to what level of FV is needed to achieve the purpose of hemostasis, and it is generally believed that 25% is sufficient. In general, fresh plasma should be transfused 10~15ml/kg each time when bleeding, and once in 12 h if necessary; plasma should be transfused 15~25ml/kg before surgery and 10~15ml/kg after surgery for 5~10d.