The normal reference value of prothrombin time is 11-13s, and a prolongation of more than 3s is clinically significant. Prothrombin time is a screening test that reflects the human exogenous coagulation pathway, and also reflects the synthetic function of the liver. Prolonged prothrombin time indicates that the human exogenous coagulation factors are impaired, and prolonged prothrombin time is commonly found in the following conditions: 1. vitamin K deficiency, resulting in reduced synthesis of vitamin K-dependent coagulation factors II, VII, IX, and X. 2. severe acute and chronic liver disease, resulting in decreased liver synthesis of The function of coagulation factors is decreased. 3, Disseminated intravascular coagulation, leading to increased consumption of coagulation factors. 4, Long-term oral anticoagulants, such as warfarin, which can inhibit the synthesis of coagulation factors II, VII, IX, and X in the liver. 5, Rat poisoning, which can interfere with the utilization of vitamin K by the liver and affect the synthesis of vitamin K-dependent coagulation factors.