Platelet aggregation refers to the property of platelets to adhere to each other. In normal blood circulation, platelets are scattered, and when there is a blood vessel rupture and bleeding, platelets will aggregate and adhere to each other, forming platelet thrombus, which plays a role in stopping bleeding. In clinical practice, the platelet aggregation rate is usually measured to reflect the function of platelets. A decrease in platelet aggregation rate makes the patient prone to bleeding, which is commonly seen in primary thrombocytopenic purpura, myelodysplastic syndrome, acute leukemia, and also in platelet anemia and giant platelet syndrome. Also, application of certain anti-platelet drugs such as aspirin, dipyridamole, heparin, etc., can result in a decrease in platelet aggregation. Increased platelet aggregation is commonly seen in pre-thrombotic states or thrombotic disorders, such as acute myocardial infarction, cerebral thrombosis, etc.