The main danger of high platelets is the easy formation of blood clots, such as cerebral thrombosis, myocardial infarction, lower extremity venous thrombosis, bleeding and so on. The normal value of platelets is (100-300) × 10^9/L. When the patient is mildly high, it usually has little effect on the human body, but if the elevation is serious, it is easy to develop coagulation disorders and blood clots. Platelet increase, the body’s blood will be hyperviscosity blood, blood flow slows down, blood flow to the narrowing of blood vessels will be easily blocked, and the formation of thrombus infarction. 1. Cerebral thrombosis: If the thrombus is obstructed to the brain, symptoms such as dizziness, headache, numbness of hands and feet may occur in mild cases, and hemiplegia may be caused in serious cases, which may even threaten the patient’s life. 2. Myocardial infarction: If the thrombus is obstructed to the cardiovascular system, myocardial infarction will be easily triggered, and the common symptom is angina pectoris or burning sensation in the chest. In severe cases, cardiac arrest and shock may occur, which may endanger the patient’s life. 3. Lower extremity venous thrombosis: Due to the effect of gravity, it is difficult to return blood to the lower extremities, and if the blood is in a high viscous state, the blood flow will be even slower, and it will be easier to form a thrombus, especially for the patients who are bedridden for a long period of time, and who have a history of venous thrombosis, which is more likely to happen. 4. Bleeding: often spontaneous, can be repeated episodes, gastrointestinal bleeding is common, but also epistaxis, gum bleeding, hematuria, skin and mucous membrane petechiae. In addition to the above hazards, high platelets may also cause many diseases. Therefore, if the above test results occur, it is recommended to go to the hospital in time to find out the cause of the disease as early as possible and carry out regular treatment.