Lymphocytosis is an increase in the number or proportion of lymphocytes in the blood.

Absolute lymphocytosis is the condition where there is an increase in the lymphocyte count beyond the normal range while relative lymphocytosis refers to the condition where the proportion of lymphocytes relative to white blood cell count is above the normal range.

[1] Lymphocytes normally represent 20% to 40% of circulating white blood cells.

In the elderly, lymphoproliferative disorders, including chronic lymphocytic leukemia and lymphomas, often present with lymphadenopathy and a lymphocytosis.

[13] The lymphocyte count can also be directly measured by flow cytometry.