Leukopenia is a disease caused by unknown reasons and secondary to other diseases. It is divided into two categories: primary and secondary. A decrease in the number of white blood cells will weaken the body's ability to resist bacteria and make it more susceptible to infection. However, leukopenia does not necessarily require treatment. First, it depends on the degree of reduction; second, it depends on the cause of the reduction. When the number of white blood cells in the peripheral blood is continuously lower than 4x109/L, it is generally called leukopenia. If the total number of white blood cells is significantly reduced, lower than 2x109/L, the absolute value of neutrophils is lower than 0.5x109/L, or even disappears, it is called agranulocytosis.