Leukocytes are mainly composed of neutrophils, monocytes, eosinophils, basophils and lymphocytes, so two indicators of the percentage and absolute value of these cells are present in routine blood tests. A peripheral blood leukocyte count that is consistently below 3.5 x 109/L is considered below normal and is referred to as leukopenia, the most common of which is neutropenia. There are many causes of neutropenia, and the common causes are as follows: certain viral infections or sepsis can cause excessive depletion of leukocytes at the site of inflammation; autoimmune system diseases such as hypersplenism, certain hepatitis or systemic lupus erythematosus can also destroy leukocytes in the body, leading to a decrease in their number; diseases affecting human hematopoietic stem cells, such as aplastic anemia, myelodysplastic syndrome, and Diseases affecting human hematopoietic stem cells, such as aplastic anemia, myelodysplastic syndrome, metastatic cancer of bone marrow and other neoplastic diseases, can affect the production and maturation of leukocytes, resulting in a decrease in leukocytes. In addition, abnormal distribution of neutrophils in the body can also lead to a decrease in their absolute value, a condition that does not lead to significant complications. Neutrophils ≥1.0×109/L are considered mildly reduced. Patients with mildly reduced neutrophils may not have specific clinical symptoms, or may only have mild discomfort such as low fever and malaise. Neutropenia of (0.5-1.0)×109/L is moderate reduction, and neutrophils <0.5×109/L is severe reduction, of which severe neutropenia is also known as neutrophil deficiency, referred to as "granulocytosis". Moderate and severe neutropenia are prone to infections and non-specific symptoms such as fatigue, weakness, dizziness, loss of appetite, etc. The common sites of infection are respiratory tract, gastrointestinal tract and genitourinary tract, which can lead to headache, high fever, mucosal necrosis, hemorrhagic ulcer, etc., and even severe sepsis or infectious shock, which can be life-threatening. Therefore, patients with granulocytopenia need to seek medical attention immediately once they become febrile. In conclusion, the treatment of leukopenia should be based on the degree and type of reduction, and more importantly, timely improvement of systematic and standardized examination to identify the underlying cause of leukopenia, and relevant treatment to achieve the root cause.