Lymphocytes are a type of white blood cell that play an essential role in the immune system, helping the body fight infections. A high lymphocyte count, also known as lymphocytosis, means having a higher-than-normal amount of lymphocytes in the blood. A temporarily high lymphocyte count usually means that the body is working as it should to protect against germs that make you sick. However, a high lymphocyte count can also indicate a more serious condition, such as a blood cancer or a chronic infection.

Some causes of lymphocytosis include:

• Infections, including bacterial, viral, or other types of infections
• Chronic lymphocytic leukemia
• Acute lymphocytic leukemia
• Lymphoma
• Hepatitis
• HIV and AIDS
• Syphilis
• Tuberculosis
• An underactive thyroid (hypothyroidism)
• Mononucleosis
• Whooping cough

It is important to note that a high lymphocyte count does not always indicate a serious condition, and it is usually temporary and harmless. However, if the lymphocyte count remains high, further tests may be needed to determine the cause. If you are concerned about your lymphocyte count, it is best to talk to a healthcare provider to determine the underlying cause and appropriate treatment, if necessary.