A person who has lymphocytosis, or a high lymphocyte count, likely suffers from an infection, autoimmune disorder or cancer of the lymphatic system or blood. Physicians perform a variety of tests on patients presenting with a high lymphocyte count, depending on factors that indicate specific conditions, according to Mayo Clinic.
In the majority of cases, a high lymphocyte count is not cause for serious concern. When the body is fighting an infection, lymphocyte counts go up as the body sends this type of cell to fight the invading viral or bacterial infection. As soon as the body defeats the infection, the lymphocyte count resolves to normal levels, explains Mayo Clinic.
When lymphocyte counts remain elevated for an extended period of time, physicians run tests to find the underlying cause. Sometimes the cause is a bacterial or viral infection that has gone undetected. However, conditions such as chronic or acute lymphocytic leukemia, mononucleosis, tuberculosis, vasculitis and HIV/AIDS also present with a high lymphocyte count, notes Mayo Clinic. Each of these conditions has its own testing protocol; doctors look at other symptoms to determine the proper course of action. A high lymphocyte count is often one of the first clues that helps doctors identify serious conditions in patients.