Lymphocytosis

Lymphocytosis is a condition in which the number of lymphocytes, a type of white blood cell, becomes higher than the normal range. Lymphocytes play an essential role in protecting the body against infections and supporting the immune system. Lymphocytosis may occur temporarily as the body responds to an infection or inflammation, but persistent elevation can sometimes indicate an underlying medical disorder. Common causes include viral infections such as influenza, infectious mononucleosis, hepatitis, and other respiratory infections.
Certain bacterial infections, chronic inflammatory conditions, and immune-related disorders may also contribute to increased lymphocyte counts. In some cases, persistent lymphocytosis can be associated with blood cancers such as chronic lymphocytic leukemia or other lymphoproliferative disorders.

Many people with mild lymphocytosis have no noticeable symptoms, particularly when it develops during a short-term infection. When symptoms occur, they usually relate to the underlying cause and may include fever, fatigue, swollen lymph nodes, night sweats, or unexplained weight loss. Diagnosis generally involves a complete blood count and differential blood test. If lymphocytosis persists, healthcare professionals may recommend additional investigations, including a peripheral blood smear, flow cytometry, or other specialized tests. Treatment depends on the underlying cause rather than the elevated lymphocyte count itself.