The four coagulation tests include prothrombin time, prothrombin time, partially activated prothrombin time, and fibrinogen. If these four items are normal, the following diseases can be ruled out: i. Hemophilia. Either hemophilia A, hemophilia B, or vascular hemophilia can be ruled out. II. Disseminated intravascular coagulation. Because the activity of various coagulation factors is significantly reduced in disseminated intravascular coagulation, the patient will have a significantly prolonged prothrombin time and partially activated prothrombin time. If all are normal, diffuse intravascular coagulation can be excluded. Third, vitamin K deficiency. In vitamin K deficiency, the patient will have abnormalities in the exogenous coagulation pathway, endogenous coagulation pathway, and prolonged PT and APTT due to vitamin K-related coagulation factor deficiency. If normal, vitamin K deficiency can be excluded. IV. Severe liver disease. In severe liver disease, the activity of coagulation factors producing is decreased and coagulation dysfunction can also occur. If the four coagulation items are normal, severe liver disease can also be ruled out.