Platelets 491 x 10^9/L may indicate thrombocytosis, etc. Whether or not it is dangerous depends on the severity of the patient’s condition and cannot be determined by a single value. Normally, platelets in the blood are (100~300) x 10^9/L. When the platelet count is greater than 400 x 10^9/L, it is a case of thrombocytosis. Thrombocytosis may be caused by primary thrombocythemia or by diseases such as primary myelofibrosis, true erythrocytosis, myelodysplasia, chronic thrombocythemia, and other myeloproliferative abnormalities. In addition, thrombocytosis can occur in diseases such as anemia, acute blood loss, infections, and malignancies. However, the specific seriousness of the patient’s condition should be considered comprehensively according to his or her own condition, personal constitution, and whether there are serious complications, and cannot be clarified by only one indicator. It is recommended that the patient should consult a doctor for examination in time, and after clarifying the specific cause of the disease, actively carry out treatment.