The white blood cell differential assesses the ability of the body to respond to and eliminate infection. It also detects the severity of allergic and drug reactions plus the response to parasitic and other types of infection. It is essential in evaluating the reaction to viral infections and response to chemotherapy. It can also identify various stages of leukemia. There are five types of white blood cells, each with different functions: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The differential reveals if these cells are present in normal proportion to one another, if one cell type is increased or decreased, or if immature cells are present. The count can be expressed as a percentage (in relation to the total WBC) or as an absolute value (percentage x total WBC). Of these, the absolute value is much more important than the relative value. NEUTROPHILS increase in response to bacterial infection or inflammatory disease. EOSIONOPHILS increase in response to allergic disorders, inflammation of the skin, and parasitic infections. BASOPHILS increase in cases of leukemia, chronic inflammation, the presence of a hypersensitivity reaction to food, or radiation therapy. LYMPHOCYTES can increase in cases of viral infection, leukemia, cancer of the bone marrow, or radiation therapy. MONOCYTE levels can increase in response to infection of all kinds as well as to inflammatory disorders. See Leukocytes Count, Total