Whether platelets above 500 x 10⁹/L are dangerous or not depends on the cause of their elevation, including primary and secondary increases. The normal value of platelets is (100~300)×10⁹/L. Platelets higher than 500×10⁹/L have significantly exceeded the normal range and should be taken seriously. 1. Thrombocytosis can be seen in primary thrombocytosis, commonly seen in myeloproliferative diseases, such as chronic granulocytic leukemia, true erythrocytosis, primary thrombocythemia. 2. Thrombocytosis is also seen in secondary thrombocytosis, which is commonly seen in acute and chronic inflammatory diseases, iron deficiency anemia, and so on. Splenectomy can also lead to thrombocytosis. In the case of leukemia, it is more dangerous and more severe, requiring aggressive chemotherapy and, if necessary, bone marrow transplantation, with drugs such as cytarabine. If it is inflammation, platelets will gradually return to normal after aggressive anti-inflammatory treatment, with drugs including levofloxacin, etc. It is usually less dangerous and the condition is mostly not serious. In case of splenectomy, it is also usually not dangerous, and platelets will slowly fall to the normal range after a period of time. When platelets are higher than 500 x 10⁹/L, patients should do the next step of examination and treatment under the guidance of a doctor.