Leukocyte 10.9×10^9/L is a mild increase in the number of white blood cells. Whether leukocyte 10.9×10^9/L is serious or not depends on the specific cause of the mild increase in leukocytes, for example, a healthy person can have a mild increase in leukocytes just after a full meal during a routine blood test, or after strenuous exercise, or when emotionally excited, or in a hot or cold environment. In this case, a leukocyte of 10.9×10^9/L is not a problem and the consequences are not serious. However, if the leukocyte 10.9×10^9/L is accompanied by anemia and thrombocytopenia, leukemia cannot be ruled out, and the diagnosis of acute leukemia can often be confirmed by bone marrow aspiration, through bone marrow morphology, cytogenetics, immunology, molecular biology, etc. The consequences of this condition are very serious. Therefore, the severity of leukocyte 10.9×10^9/L cannot be determined simply by the number of leukocytes, but depends on the specific cause of the increased number of leukocytes.