When platelets are at (400-500) x 10⁹/L, the count is high. As for how serious it is, it needs to be analyzed in the context of the patient’s specific situation, and the cause of the disease needs to be clarified, which is commonly seen in conditions such as blood concentration and primary thrombocythemia. Diarrhea, vomiting, extensive burns, etc. can lead to blood concentration, which in turn causes elevated platelet and red blood cell counts. This elevation is relative. After targeted rehydration, platelets can all return to the normal range and are generally not serious as far as platelets are concerned. Primary thrombocythemia can have absolute elevation of platelets, which can lead to thrombosis, bleeding, etc. Especially for elderly patients, when combined with hypertension, hyperglycemia, hyperlipidemia, coronary artery disease, cerebral thrombosis and other underlying diseases, if the platelets are at (400~500)×10⁹/L, it is easy to induce thrombosis, or even pulmonary embolism, which may jeopardize the patient’s life. s life. This is very serious. In younger people, the effects may not be as severe as in older people. Elevated platelets can be controlled with medication or surgery. Medications include hydroxyurea and aspirin. In addition a small number of primary thrombocythemias can progress to myelofibrosis and AML/MDS and should be of high concern. So when platelets are at (400-500) x 10⁹/L is it serious or not, it needs to be analyzed on a case-by-case basis and cannot be generalized. Specific treatment should be carried out under the guidance of a physician.