There are three types of lymphocytes in the blood and lymph. B lymphocytes, responsible for the production of specific antibodies (acquired immunity); T lymphocytes, which help distinguish foreign antigens from those specific to the body; and NK (natural killer) lymphocytes capable of destroying cancer cells or cells infected with viruses. The test provides the total for the three subclasses of lymphocyte as a number per litre of blood (lymphocyte #) and as a fraction of the total white blood cells (lymphocyte ratio). Results must be interpreted in light of clinical observations, other results from the current blood count, and variations in results over time.
A high number or ratio of lymphocytes (lymphocytosis) is found in acute viral infections (hepatitis, chicken pox, rubella, etc.) and some bacterial infections (tuberculosis, pertussis/whooping cough, etc.). Lymphocytosis is also found in lymphocytic leukemia and lymphoma.
A reduced number or ratio of lymphocytes (lymphopenia or lymphocytopenia) is found in autoimmune diseases (lupus, rheumatoid arthritis, etc.), certain infections (HIV, tuberculosis, hepatitis, influenza), bone marrow disorders (caused by chemotherapy or radiotherapy, for example) and immune deficiencies like AIDS and certain congenital immunodeficiencies.