The normal value of neutrophils is 40%~75% of the total number of white blood cells, and the normal count of healthy adults is (1.80~6.30) x 10^9/L. Neutrophils are non-specific immune cells in the human body, which have strong chemotaxis, phagocytosis and bactericidal effects, thus clearing up foci of infection in the body. Elevated or decreased neutrophil counts are important indicators of disease: 1. Neutrophilia is common in acute septic infections, uremia, lead poisoning, mercury poisoning, malignant tumors, leukemia and so on; 2. Neutropenia is common in typhoid fever, paratyphoid fever, measles, influenza and other infectious diseases, malignant tumors after chemotherapy or radiotherapy, certain blood diseases (such as aplastic anemia, granulocyte deficiency, myelodysplastic syndromes, etc.) and hypersplenism. Neutrophils play a huge role in the human body, and when neutropenia or hyper neutrophilia occurs, further examination should be actively conducted to find out the cause, so that timely intervention can be made under the guidance of physicians at the early stage of the disease to prevent aggravation of the condition.