A persistent total peripheral blood leukocyte count below 4 x 109/L is called leukopenia. Leukopenia is most commonly caused by neutropenia. When the absolute value of neutrophils is below 1.8-2.0×109/L, it is called granulocytopenia. A reduction to less than 0.5-1.0×109/L is called granulocyte deficiency and is often associated with severe uncontrollable infections. The etiology and pathogenesis of the above three types of conditions are roughly the same, but the severity of the condition varies. Xue Mei, Blood Disorders Research Center, Air Force General Hospital