Leukocytes are a very important type of blood cell in the human blood, and they carry out many important tasks in the human body. It has the role of phagocytosis and production of antibodies, the ability to heal the body from damage, the ability to resist invasion by pathogens, and the immune resistance to disease. Leukocytes can be subdivided into five types, and counting each of these five types of cells using instruments or manual methods is called leukocyte sorting. Of these five types of leukocytes, neutrophils account for 50-70%, lymphocytes for 20-40%, monocytes for 3-8%, eosinophils for 1-5%, and basophils for no more than 1%. When the body is not well, it usually shows itself through changes in the number of white blood cells. If the number of white blood cells is higher than 10,000/mL, it is an elevated white blood cell count, and if the number of white blood cells is lower than 4,000/mL, it is a decreased white blood cell count.