Lymphocytopenia
Lymphocytopenia is an abnormally low number of lymphocytes in the blood.
Lymphocytes usually constitute 20 to 40% of all white blood cells in the bloodstream. The lymphocyte count is normally above 1,500 cells per microliter of blood in adults and above 3,000 cells per microliter of blood in children. A reduction in the number of lymphocytes may not cause a significant decrease in the total number of white blood cells.
A variety of diseases and conditions, including infection with human immunodeficiency virus (HIV)--the virus that causes AIDS, can decrease the number of lymphocytes in the blood. Also, the number of lymphocytes can decrease briefly during times of severe stress and during use of corticosteroids (such as prednisone), chemotherapy for cancer, and radiation therapy. Severe reduction in lymphocytes can occur in certain hereditary disorders (the hereditary immunodeficiency diseases (see Section 16, Chapter 184)).
There are three types of lymphocytes: B lymphocytes, T lymphocytes, and natural killer cells, all of which have very important functions in the immune system. Too few B lymphocytes can lead to a decrease in the number of plasma cells and reduced antibody production. People who have too few T lymphocytes or too few natural killer cells have problems controlling certain infections, especially viral, fungal, and parasitic infections. Severe lymphocyte deficiencies can result in uncontrolled infections that can be fatal.
 See the sidebar Causes of Lymphocytopenia.
Symptoms and Diagnosis
Mild lymphocytopenia may cause no symptoms and is usually detected by chance when a complete blood cell count is conducted for other reasons. Drastically reduced numbers of lymphocytes lead to infections with bacteria, viruses, fungi, and parasites.
When the numbers of lymphocytes are drastically reduced, a doctor usually takes a sample of bone marrow to examine under a microscope (bone marrow biopsy). The number of specific types of lymphocytes (T lymphocytes, B lymphocytes, and natural killer cells) can also be determined in the blood. A decrease in certain types of lymphocytes may help a doctor diagnose some diseases, such as AIDS or certain hereditary immunodeficiency disorders.
Treatment
Treatment depends mainly on the cause. Lymphocytopenia caused by a drug usually begins to resolve within days after a person stops taking the drug. If the lymphocytopenia is the result of AIDS, combination therapy with at least three antiviral agents of different classes can increase the number of T lymphocytes and improve survival.
Gamma globulin (a substance rich in antibodies) may be given to help prevent infections in people with too few B lymphocytes (who therefore have a deficiency of antibody production). People with a hereditary immunodeficiency may benefit from bone marrow (stem cell) transplantation. If an infection develops, a specific antibiotic, antifungal, antiviral, or antiparasitic drug directed against the infective organism is given.
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