Infections, blood or lymphatic cancers, and autoimmune disorders that lead to chronic inflammation are possible causes of a high lymphocyte count, also called lymphocytosis, states Mayo Clinic. In particular, conditions associated with lymphocytosis include cytomegalovirus infection, chronic or acute lymphocytic leukemia, and AIDS.
Whooping cough, vasculitis, tuberculosis and multiple myeloma may also cause a low lymphocyte count, according to Mayo Clinic. Patients with lymphocytosis sometimes exhibit few or no symptoms at all. Doctors order further tests to diagnose the condition accurately and determine if the high lymphocyte count is a benign, short-term condition or if it indicates a serious underlying cause.
Lymphocytes are white blood cells that play an essential role in combating illnesses, which is why the body's lymphocytes count sometimes increases temporarily after an infection, notes Mayo Clinic. Adults with lymphocytosis generally have a lymphocyte count above 3,000 lymphocytes per microliter of blood. The range of high lymphocyte count in children differs according to age, but it typically reaches around 7,000 to 9,000 lymphocytes per microliter.
The blood differential test measures white blood cell count and involves obtaining blood from the vein and storing the blood sample in an airtight container, explains MedlinePlus. A low lymphocyte count may occur in patients with leukemia or HIV infection or patients who are exposed to chemotherapy or radiation therapy.