The normal range of leukocytes is between (4-10) x 10^9/L. Leukocytes below normal values are called leukopenia. The main role of leukocytes is to destroy various pathogenic microorganisms and also to remove allergens as well as senescent, dead and abnormal cells, which play a role in purifying the blood and maintaining the normal functioning of various systems. If leukocytes are reduced, the most important result is susceptibility to various infections, including bacteria, viruses, fungi, tuberculosis, as well as mycoplasma and chlamydia. In mildly depressed leukocytes (leukocytes between (3-4) x 10^9/L), serious infections usually do not occur, and some patients may experience dizziness, weakness, and limb weakness. In this case, when neutrophils (a type of white blood cell) are <0.5×10^9/L, it is called granulocyte deficiency. When this condition occurs, the self resistance is close to 0, which makes it easy to have various infections and life-threatening, and such infections are serious infections that spread more easily and deteriorate rapidly. If toxic shock and multiple organ failure occur, the death rate is high. Therefore, if you find hypocellularity, you should go to the hematology department in time to identify the cause and give timely treatment.