A normal lymphocyte range is generally between 20 and 40 percent in healthy individuals. A lymphocyte range is part of a blood differential test, which measures the percentage of each kind of white blood cell in the blood. It is used to diagnose and monitor anemia, leukemia and infection.
Lymphocyte cells, which are classified as T cells or B cells, determine the body's immune response to infections and foreign substances. Some possible causes for an increased percentage of lymphocytes in the blood include multiple myeloma, chronic bacterial infections, lymphocytic leukemia and viral infections. The percentage of lymphocytes may decrease as a result of chemotherapy, HIV infection, leukemia, radiation therapy and steroid use.