A high percentage of lymphocytes in a blood differential is an indicator of chronic bacterial infection, lymphocytic leukemia, multiple myeloma and viral infections, reports MedlinePlus. Lymphocytes are a type of white blood cell.
Because lymphocytes help fight infection, it is normal to see an increased number of lymphocytes in the blood following an infection, according to Mayo Clinic. Cytomegalovirus, tuberculosis, mononucleosis and whooping cough are some of the infections associated with an increased lymphocyte count. A person's lymphocyte count may also be elevated due to the chronic inflammation caused by an autoimmune disorder or due to the presence of lymphatic cancer or blood cancer.