Platelets up to 1000 x 10⁹/L are considered severely elevated and can often indicate hematological disorders such as myeloproliferative neoplasms, which require high attention. Thrombocytosis can be categorized into primary increase and reactive increase. 1. Primary thrombocytosis is common in myeloproliferative neoplasms, such as true erythrocytosis, primary thrombocythemia, early stage of primary myelofibrosis, and chronic granulocytic leukemia, etc. Reactive thrombocytosis is common. 2. Reactive increase is common in acute infection, acute hemolysis and some cancer patients. However, reactive thrombocytosis is often mild, with counts below 500×10⁹/L. Therefore, platelets up to 1,000×10⁹/L belong to primary thrombocytosis. Severe increase in platelet counts may cause increase in blood viscosity, which may lead to thrombosis and embolic disease, and a large number of platelet aggregates may cause damage to the endothelial cells of blood vessels, which may lead to hemorrhagic disease. Therefore, patients need to consult a doctor in a timely manner, determine the cause of the disease through further examination, and actively treat the disease under the guidance of the physician.