Lymphocytosis (lim-foe-sie-TOE-sis), or a high lymphocyte count, is an increase in white blood cells called lymphocytes. Lymphocytes help fight off diseases, so it's normal to see a temporary increase 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. It can be as high as 9,000 lymphocytes per microliter. The exact thresholds for lymphocytosis can vary slightly from one lab to another.
July 12, 2019
- Bain BJ, et al., eds. Approach to the diagnosis and classification of blood cell disorders. In: Dacie and Lewis Practical Haematology. 12th ed. London, Eng: Elsevier; 2017. https://www.clinicalkey.com. Accessed June 20, 2019.
- Davids MS. Approach to the adult with lymphocytosis or lymphocytopenia. https://www.uptodate.com/contents/search. Accessed June 20, 2019.
- AskMayoExpert. Lymphocytosis. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2019.
- Coates TD. Approach to the child with lymphocytosis or lymphocytopenia. https://www.uptodate.com/contents/search. Accessed June 20, 2019.
- Kaushansky K, et al., eds. Lymphocytosis and lymphocytopenia. In: Williams Hematology. 9th ed. New York, N.Y.: McGraw-Hill Education; 2016. https://accessmedicine.mhmedical.com. Accessed June 20, 2019.