Leukopenia refers to a condition where the absolute count of white blood cells in peripheral blood persistently falls below 4.0×10^9/L, commonly known as leukopenia. There are many causes of leukopenia, which can generally be divided into two categories: defects in white blood cell production, and excessive destruction or consumption. Common causes include certain chemicals, radiation, cytotoxic drugs, some hematological diseases such as aplastic anemia and myelodysplastic syndrome, as well as Vitamin B12 deficiency, and drugs used to treat hyperthyroidism. Additionally, viral infections can lead to excessive white blood cell consumption and result in leukopenia. Therefore, when leukopenia occurs, it is crucial to actively search for the underlying causes and treat the primary condition. Meanwhile, if the patient's white blood cell count is significantly reduced, drugs that increase white blood cells may be temporarily administered to elevate the patient's white blood cell count.