Lymphocytic leukocytosis is an abnormally high number of lymphocytes (a type of white blood cell) in the blood.
The number of lymphocytes can increase in response to infections, especially by viruses. Some bacterial infections, such as tuberculosis, may also increase the number. Certain types of cancer, such as lymphomas and acute or chronic lymphocytic leukemia, may produce an increase in the number of lymphocytes, in part by releasing immature lymphocytes (lymphoblasts) or the lymphoma cells into the bloodstream. Graves disease and Crohn disease may also result in an increase in the number of lymphocytes in the bloodstream.
When the number of lymphocytes increases, symptoms may result from the infection or other disease that has caused the number of lymphocytes to increase, rather than from the increase in lymphocytes per se. When an infection is suspected, doctors may do blood tests. When doctors discover an increased number of lymphocytes, a blood sample is examined under a microscope to determine if the lymphocytes in the bloodstream appear activated (as occurs in response to viral infections) or if they appear immature or abnormal (as occurs in certain leukemias or lymphomas). They can also identify the specific type of lymphocyte (T cells, B cells, natural killer cells) that is increased to help determine the underlying problem.
Treatment for lymphocytic leukocytosis depends on the cause.
Last full review/revision January 2013 by Mary Territo, MD