White blood cells 15×10^9/L is not necessarily leukemia, it can also be caused by infections, drug effects and other reasons. 1. Infection: first of all, white blood cells belong to immune cells, which are an important part of the body’s defense system. When an infection occurs, the white blood cells in the peripheral blood will gradually increase, phagocytose germs and produce antibodies. 2. Drugs: If you use hormone drugs such as dexamethasone for a long time, it is easy to stimulate the human bone marrow, so that the bone marrow will proliferate and produce more white blood cells at the same time. 3. Leukemia: Leukemia belongs to hematopoietic stem cell disease, which will cause cell differentiation to stagnate in the primitive state. And when the primitive cells keep entering the peripheral blood, it will cause leukocytosis. Normally, the white blood cell value of a normal person is around (4~10)×10^9/L. If the white blood cell value is 15×10^9/L, it means that the white blood cell value is in an elevated state, and you should consult a doctor as soon as possible to find out the cause of the disease, and follow the doctor’s instructions to carry out standardized treatment.