1.Overview Platelet aggregation (PAg) is one of the main functions of platelets, which refers to the adhesion between platelets and platelets, showing the characteristics of activated platelets interacting and aggregating into clusters. This phenomenon can be induced by continuous mixing of platelet-rich plasma (PRP) or whole blood (WB) with an aggregation agent (also called inducer). The maximum aggregation rate of ADP is 62.7±16.1%, and the aggregation curve varies depending on the method and the inducer. 2.Clinical application The main clinical applications are: (1) Routine screening, can be used for health checkups, to detect whether the blood has a tendency to hypercoagulation. (2) Regular testing for hypertension, diabetes, cerebrovascular disease, hyperlipidemia, ischemic encephalopathy, nephrotic syndrome, gestational hypertension and diabetes. (3) Preoperative testing, when platelet coagulation is significantly reduced, or aspirin, if platelet coagulation is significantly reduced then there is a risk of intraoperative bleeding. (4) Efficacy testing of antiplatelet drugs. Because of the long course of antiplatelet drug therapy, monitoring should be given during treatment to avoid the adverse effects of severe bleeding and to facilitate efficacy prediction. 3.Clinical significance Increase: diabetes, acute myocardial infarction, venous thrombosis, high beta lipoproteinemia, antigen-antibody complex reaction, artificial valve, oral contraceptives, high-fat diet and smoking, etc. Decreased: platelet anemia, giant platelet syndrome, storage pool disease, May-Heegglin abnormality, low (no) fibrinogenemia, cirrhosis, uremia, infective endocarditis, taking anti-platelet drugs, etc.