Whether a white blood cell of 1.9 x 10^9/L is serious or not needs to be judged in relation to the cause of the disease, such as drug-induced depression, which is relatively not serious, and blood tumors and other causes of relative seriousness. The normal range of white blood cell count in adults is 4.0~10.0×10^9/L. When the white blood cell count is lower than 4.0×10^9/L, it is considered low. The severity of the condition needs to be judged in relation to the specific cause. Leukopenia can be seen in drug damage, such as isoniazid and rifampicin. When the diagnosis of drug damage leads to a white blood cell count of 1.9×10^9/L, the condition is relatively mild, and the white blood cell count can rise slowly after stopping the drug as prescribed by the doctor. There are also immune disorders such as systemic lupus erythematosus and hematologic tumors such as lymphoma and myeloma that can lead to low white blood cell counts, and the patient’s risk of infection can be significantly increased. When the white blood cell count is 1.9×10^9/L, it often suggests that the condition has become more serious and the primary disease needs to be actively treated. After the white blood cell reduction, it is recommended to consult a doctor in time to clarify the diagnosis and standardize the treatment.