A white blood cell count of 19.9 x 10^9/L over the normal value (4-10) x 10^9/L is relatively serious. Elevated white blood cell count is mostly seen in infections, leukemia, acute hemorrhage and so on. 1. Infection: acute infection caused by pathogens invading the body can lead to elevated white blood cell counts, and when it reaches 19.9×10^9/L, it suggests that the infection is relatively serious, and anti-infection treatment should be actively carried out. 2. Leukemia: Leukemia belongs to the malignant clonal disease of hematopoietic stem cells, due to the uncontrolled proliferation of leukemia cells, differentiation disorders, apoptosis is blocked, and stagnation in different stages of cell development. Routine blood tests show abnormally high platelets, leukocytes, abnormally high leukocyte ratio or count, and the condition is more serious. 3. Acute hemorrhage: acute hemorrhage caused by vomiting blood, urinating blood, or skin bleeding due to trauma, etc. There is usually no blood routine abnormality when the amount of bleeding is small. More bleeding and serious tissue damage can lead to elevated white blood cell count, and the condition is also more serious, which requires timely treatment to prevent deterioration of the condition. Elevated white blood cell counts are also seen in hemolysis and myeloproliferative neoplasms. When the white blood cell count is 19.9×10^9/L, it is recommended to identify the cause and standardize the treatment.