For venous blood draws from the skin, at least 5 minutes of compression is required to ensure successful aggregation and adhesion of platelets at the destruction of the vessel, forming microthrombi and providing a complete hemostasis. If the pressure is not strong enough, or if the pressure time is too short, there will be varying degrees of blood leakage into the subcutaneous cavity, forming a local bruise. Platelets produce effects relatively quickly, especially in people with normal coagulation, and the release from platelet adhesion aggregation to form microthrombi is a very rapid process that will begin to form the moment a blood vessel is damaged. But complete hemostasis also requires the fibrinolytic system, as well as most of the coagulation factors in the body to participate together to complete, so it is important to give appropriate pressure and prolong the hemostasis time.