Whether platelet high 421 x 10^9/L is serious or not needs to be judged in conjunction with the original disease, such as platelet high caused by iron deficiency anemia, acute infection, and primary thrombocythemia, when the original disease is corrected, the prognosis is better, and it is usually not serious. But platelet rise caused by chronic granulocytic leukemia, etc. is more serious and has a poorer prognosis. 1. Iron deficiency anemia: it will lead to platelet rise, usually manifested as a mild rise, resulting in such phenomenon as high platelet 421×10^9/L. Generally, it can be treated with oral iron, such as ferrous sulfate, and combined with vitamin C to promote the absorption of iron, the prognosis is better, and this condition is not serious. 2. Acute infections: some acute infections, such as pneumonia, acute enteritis, etc. may lead to platelet rise, platelet high 421×10^9/L, after actively controlling the primary disease, such as levofloxacin anti-infection treatment, platelets will be reduced back to the normal level, does not affect the life, generally not serious. 3. Primary thrombocythemia: hydroxyurea, aspirin and other drugs can be given to control the platelet level, it is difficult to completely cure, but can be effectively prolonged survival through drug treatment. 4. Chronic granulocytic leukemia: mainly manifested as anemia, recurrent infections, bleeding tendency, splenomegaly and other symptoms, which are more serious and need to be treated with drugs such as imatinib and hydroxyurea in time. Platelet high 421×10^9/L, and other conditions, it is recommended to consult a doctor in a timely manner to identify the causes and cooperate with the doctor for treatment. The above medication is in accordance with the doctor’s prescription.