Normal lymphocyte counts in an adult range from 1,000 to 4,800 lymphocytes per microliter of blood, according to the National Heart, Lung and Blood Institute. Lymphocytes are certain kinds of white blood cells that comprise 20 to 40 percent of the total white blood cell count.
Lymphocytes, produced in the bone marrow with other types of blood cells, help prevent infection in the body. There are certain conditions, either inherited or acquired, that can cause problems leading to lymphocytopenia, or low counts of lymphocytes, states the National Heart, Lung and Blood Institute. While lymphocytopenia may not cause any symptoms or problems, it can lead to serious infections that require medication or treatment.