The usual term blood picture generally refers to the white blood cells in the blood count. Low blood count also refers to leukopenia. Clinical causes of leukopenia are many, in general, there are several reasons: 1, infectious diseases, viral infections are the most common causes of leukopenia, such as influenza, measles, viral hepatitis and so on. In addition, some bacterial infections, such as typhoid fever bacillus infection can also cause leukopenia. 2, for the elderly and frail or chronic wasting disease, malignant tumors, in serious infections, white blood cells sometimes do not rise rather than fall. 3, blood system diseases, such as aplastic anemia, granulocytopenia, granulocyte deficiency, and some patients with leukemia, white blood cells can also be reduced. 4, the blood system diseases, such as aplastic anemia, granulocytopenia, granulocyte deficiency, leukocytes can be reduced. 4, exposure to radiation or certain drugs, such as antipyretic and analgesic drugs, antitumor drugs, antithyroid drugs, can also cause a decrease in white blood cells.