The four coagulation items are tests for coagulation function, including activated partial thromboplastin time (APTT), prothrombin time (PT), fibrinogen (FIB) and prothrombin time (TT). 1. Activated partial thromboplastin time (APTT): a sensitive screening test reflecting the coagulation activity of the endogenous coagulation system. It is used to determine the defects of coagulation factors of endogenous coagulation pathway, and also used for initial screening of bleeding disorders and laboratory monitoring of heparin anticoagulation therapy. The normal value is 23~37 seconds. 2. Prothrombin time (PT): it is a screening test to check the total coagulation status of coagulation factors of exogenous coagulation system. It can reflect the activity of coagulation factors I, II, V, VII and X in plasma. The normal value is 11~13 seconds. 3. Fibrinogen (FIB): it is a glycoprotein synthesized and secreted by liver cells, which is involved in the production of fibrin in the process of coagulation and hemostasis. High fibrinogen indicates that the blood is in a hypercoagulable state, which is an important risk factor for various thrombotic diseases. Normal value in plasma is 2-4g/L. 4. Thrombin Time (TT): It is the time for blood to clot after the addition of standardized thrombin to plasma. In the common coagulation pathway, the generated thrombin converts fibrinogen to fibrin, which can be reflected by TT. The normal value is 16 to 18 seconds, and more than 3s above the normal control is abnormal. Coagulation four can understand the test person coagulation function is normal, but also can determine the use of antithrombotic drugs, such as test results are abnormal need to seek medical help in a timely manner.