(1)A smaller than normal number of white blood cells, lymphocytes, in the blood circulation, occuring as a blood disorder or in association with nutritional deficiency, cancer, or infectious mononucleosis.
(2)Lymphocytopenia is a total lymphocyte count of < 1000/μL in adults or < 3000/μL in children < 2 yr. Sequelae include opportunistic infections and an increased risk of malignant and autoimmune disorders. If the CBC reveals lymphocytopenia, testing for immunodeficiency and analysis of lymphocyte subpopulations should follow. Treatment is directed at the underlying cause.
The normal lymphocyte count in adults is 1000 to 4800/μL; in children < 2 yr, 3000 to 9500/μL. At age 6 yr, the lower limit of normal is 1500/μL. Both B and T cells are present in the peripheral blood; about 75% of the lymphocytes are T cells and 25% B cells. Because lymphocytes account for only 20 to 40% of the total WBC count, lymphocytopenia may go unnoticed when WBC count is checked without a differential.
Almost 65% of blood T cells are CD4+ (helper) T cells. Most patients with lymphocytopenia have a reduced absolute number of T cells, particularly in the number of CD4+ T cells. The average number of CD4+ T cells in adult blood is 1100/μL (range, 300 to 1300/μL), and the average number of cells of the other major T-cell subgroup, CD8+ (suppressor) T cells, is 600/μL (range, 100 to 900/μL).
See also: Lymphopenia