The normal value of leukocytes in children is (5-12) × 10^9/L. If the leukocytes are increased, the majority are infections. Leukopenia: A peripheral blood leukocyte count below 4.0×10^9/L due to various causes is leukopenia, which can be seen in conditions such as hypersplenism, myelodysplastic syndrome, and adverse drug reactions. 1, leukocyte count: The leukocytes that can be seen in the peripheral blood can be divided into five types: neutrophils, eosinophils, basophils, lymphocytes and monocytes. The so-called leukocyte classification count is to calculate the percentage of various leukocytes in its total number, the normal value is: neutrophils: 50% to 70%; eosinophils: 0.5% to 5%; basophils: 0 to 1%; lymphocytes: 20% to 40%; monocytes: 1% to 8%. 2. In addition to the changes that can be caused by disease factors, the value of white blood cells is also affected by physiological factors and other factors. Post-meal and strenuous exercise, cold, pain, and fear can cause an increase in leukocytes; leukocytes are higher in winter than in summer, and the afternoon examination is higher than the early morning. Although external factors have an effect on leukocytes, their values generally do not change much. Leukocyte testing in children is used to initially determine the presence of infections or blood system disorders.