Lymphocytosis

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Overview

Lymphocytosis is an increase in the number or proportion of lymphocytes in the blood, usually detected when a complete blood count is routinely obtained. Lymphocytes normally represent 20 to 40% of circulating white blood cells. The absolute lymphocyte count (ALC) can be directly measured by flow cytometry, or calculated by multiplying the total white blood cell (WBC) count by the percentage of lymphocytes found in the differential count. For example, if the total WBC count is 30,000, and the %lymphocytes is 30, the absolute lymphocyte count is 3,000. In absolute lymphocytosis, the total lymphocyte count is elevated. In relative lymphocytosis, there is a higher proportion of lymphocytes among the white blood cells, but a normal absolute number of lymphocytes. In adults, absolute lymphocytosis is present when the absolute lymphocyte count is greater than 4000 per microliter, while relative lymphocytosis is present if the ALC is normal but the differential percentage of lymphocytes is higher than 40%. Relative lymphocytosis is normal in children under age 2.

Lymphocytosis can be a feature of infection, particularly in children. In the elderly, lymphoproliferative disorders, including chronic lymphocytic leukemia and lymphomas, often present with lymphadenopathy and a lymphocytosis.

Differential diagnosis of causes of lymphocytosis

Causes of absolute lymphocytosis include: acute viral infections, such as infectious mononucleosis (glandular fever), Epstein-Barr virus infection, and hepatitis; other acute infections such as pertussis and toxoplasmosis; chronic intracellular bacterial infections such as tuberculosis or brucellosis.

Causes of relative lymphocytosis include: age less than 2 years; acute viral infections; connective tissue diseases, thyrotoxicosis, Addison's disease, and splenomegaly with splenic sequestration of granulocytes.

In alphabetical order.

• Acute infection
• Addison's Disease
• Adenovirus
• Brucellosis
• Chickenpox
• Chronic and acute lymphocytic leukemia
• Chronic erythroleukemia
• Chronic myelogenous leukemia
• Cytomegalovirus
• Drug hypersensitivity
• Exertion
• Hairy Cell Leukemia
• Hepatitis viruses
• Herpes virus
• HIV
• Hyperthyroidism
• Immunocytoma
• Infectious mononucleosis
• Inflammatory Bowel Disease
• Measles
• Mumps
• Osteomyelofibrosis
• Pain
• Pertussis
• Polycythemia
• Postoperative
• Sarcoidosis
• Stress
• Syphilis
• Toxoplasmosis
• Trauma
• Tuberculosis
• Varicella
• Viral pneumonia
• Waldenstrom's Syndrome