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Definition
By Mayo Clinic staffLymphocytosis (lim-foe-sie-TOE-sis), or a high lymphocyte count, is an increase in white blood cells called lymphocytes (LIM-foe-sites). Lymphocytes are an important part of the immune system. They help fight off diseases, so it's normal to see a temporary rise in the number of lymphocytes after an infection.
A count significantly higher than 3,000 lymphocytes in a microliter of blood is generally considered to be lymphocytosis in adults. In children, the threshold for lymphocytosis varies with age, but may be as high as 7,000 to 9,000 lymphocytes per microliter. The exact thresholds for lymphocytosis may vary slightly from one lab to another.
- Coates TD. Approach to the patient with lymphocytosis or lymphocytopenia. http://www.uptodate.com/home. Accessed May 31, 2013.
- CBC with differential, Blood. Mayo Medical Laboratories. http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/9109. Accessed June 3, 2013
- Lichtman MA, et al. Williams Hematology. 8th ed. New York, N.Y.: The McGraw-Hill Companies; 2010. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=69. Accessed May 31, 2013.
- AskMayoExpert. What is lymphocytosis? Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2012.
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