Parents often ask: Why are my 3-year-old’s lymphocytes so high? First of all, it is important to introduce the composition of blood cells: blood cells include red blood cells, white blood cells and platelets, and white blood cells are further divided into: neutrophils, lymphocytes, monocytes, eosinophils, basophils, etc. The leukocyte classification in a child’s blood test is to see what percentage of these different types of leukocytes are present. It follows that if the percentage of neutrophils increases (e.g., 80%), the percentage of lymphocytes and other white blood cells (20%) naturally decreases. The proportion of leukocytes in normal children varies with age. In newborn infants, the proportion of granulocytes is in the majority (>60%), after 6 days the proportion of granulocytes decreases and the proportion of lymphocytes is in the majority. 4-6 years old, the proportion of granulocytes and lymphocytes is basically 50% each, and after 6 years old the proportion of granulocytes is in the majority again. Parents can simply remember: for children under 6 years old, the percentage of lymphocytes is 50-70% and the percentage of granulocytes is 30-50%. For children over the age of 6, the reverse is true: 30-50% lymphocytes and 50-70% granulocytes.