The normal range of white blood cell count is (4~10)×10⁹/L. Low white blood cell count means that the absolute value of white blood cells is below the lower limit of the normal range. Common causes include infections, hematologic diseases, autoimmune diseases and other factors. 1. Infection: pathogenic infections, especially gram-negative bacteria and viral infections, may occur in patients with low white blood cells, such patients need to choose appropriate antibiotics according to the site of infection and type of infection, such as levofloxacin. 2. Blood system diseases: when patients suffer from aplastic anemia, hemophagocytic syndrome and other blood system diseases, it will also cause a decrease in the value of white blood cells, such patients should further improve the relevant examinations to clarify the diagnosis and receive treatment. 3. Autoimmune diseases: such as systemic lupus erythematosus, rheumatoid arthritis patients will also have leukopenia. 4. Other factors: long-term use of certain drugs such as chloramphenicol, cyclophosphamide, isoniazid, etc. can also trigger a decrease in white blood cell count; some physical factors such as repeated radiation therapy patients, may also appear white blood cell count decrease. Warm reminder: when patients have low white blood cell count, they should go to the hospital in time for examination to find out the cause of the disease, and under the guidance of the doctor, to prevent the condition from worsening and delaying the condition.