A low neutrophil percentage of 37% is commonly caused by infections, hematologic diseases, physical and chemical injuries, autoimmune diseases, etc. It is recommended to consult a doctor to find out the cause and diagnose the cause. 1. Infection: bacterial infection, especially gram-negative bacillus infection, such as typhoid fever, paratyphoid fever bacillus; viral infection, such as influenza, viral hepatitis, cytomegalovirus, etc.; certain protozoan infections, such as malaria, black fever and so on. Appropriate anti-infection treatment should be taken according to the source of infection. 2. Blood system diseases: aplastic anemia, severe iron deficiency anemia, paroxysmal sleep hemoglobinuria, lymphoma and so on. The primary disease should be actively treated. 3. Physical and chemical damage: exposure to radioactive physical factors such as X-rays and γ-rays, and chemical substances such as benzene and lead can also cause low neutrophil percentages, and should be kept away from these substances. 4. In addition, hypersplenism and autoimmune diseases, such as systemic lupus erythematosus, can also cause low neutrophil percentage, and the primary disease should be actively treated. Neutrophils are a kind of white blood cells, and the percentage of neutrophils in adults accounts for about 55%~70% of the total white blood cells. Neutrophils play an important role in the body’s anti-infection, in addition to phagocytosis and destruction of invading pathogens, but also release arachidonic acid, promote thromboxane and prostaglandin generation, and regulate the caliber of the blood vessels and permeability has a significant role. When the percentage of neutrophils is low, it is recommended to consult a professional doctor to find out the cause and further diagnosis and treatment, so as not to delay the condition.