Prothrombin time, abbreviated PT, is an indicator of the exogenous coagulation pathway, with a normal range of 11-13 seconds, and more than 3 seconds above the normal control has clinical significance. The exogenous coagulation pathway refers to the activation of tissue factor, which is coagulation factor III, after the rupture of the blood vessel, then factor VII, then factor X, and then thrombin. Finally, fibrinogen is activated, which then becomes active fibrin and forms a fibrin clot, which results in hemostasis. Prolonged prothrombin time can be seen in cases of coagulation factor III, coagulation factor VII, coagulation factor X, coagulation factor II and fibrinogen deficiency. In clinical practice, prothrombin time is also prolonged in patients taking warfarin, and the International Normalized Index is often used to guide the clinical use of warfarin, with an International Normalized Index of around 2.5 being the appropriate dose.