If the white blood cell count increases, the neutrophil percentage increases, and the lymphocyte percentage decreases, the fever is considered to be caused by a bacterial infection. If the white blood cell count is normal, or if the percentage of neutrophils is decreased and the percentage of lymphocytes is increased, the fever is considered to be caused by a viral infection. If the white blood cell count increases, the lymphocyte percentage increases, and the neutrophil percentage decreases, the fever is considered to be a bacterial infection secondary to a viral infection. Therefore, changes in blood count can determine the cause of fever and then different medications can be given to treat the fever.