The normal value of prothrombin time is 13-16 seconds. If it exceeds the normal control by more than 3 seconds it has clinical significance. The method of measuring prothrombin time is to add tissue factor to the plasma and then observe the time required for the plasma to clot. Prothrombin time is a screening test for the body to respond to the exogenous coagulation pathway. If the prothrombin time is prolonged, it indicates a dysfunction of the coagulation factors involved in the body’s exogenous coagulation pathway. A prolonged prothrombin time is seen clinically in a variety of diseases, such as vitamin K deficiency, severe long-term liver disease such as cirrhosis, and disseminated intravascular coagulation. In addition, prothrombin time is also significantly prolonged in patients who are clinically anticoagulated with oral warfarin, and the dosage of warfarin can be adjusted according to the degree of prolongation of prothrombin time.