What are Lymphocytes?

lymphocytes white blood cells leukocytes cbc blood

Lymphocytes represent approximately 20 – 40% of all white blood cells.

The normal reference range for lymphocytes is between 1.5 – 3.6 cells/uL.

There are two main structural categories of lymphocytes: large granular lymphocytes and small lymphocytes.


Low lymphocyte counts are not usually significant.


  • Characteristic decreases in the lymphocyte count are usually seen late in HIV infection, as T lymphocytes (CD4+ T cells) are destroyed.
  • Steroid administration may reduce lymphocyte counts. More rarely lymphocytopenia may be caused by some types of chemotherapy or malignancies. People exposed to large doses of radiation, such as those involved with situations like Chernobyl, can have severe lymphocytopenia.



Increases in the absolute lymphocyte count are usually due to acute infections, such as Epstein-Barr virus infection and viral hepatitis. Less commonly, increased lymphocytes may be the result of pertussis and toxoplasmosis or (rarely) chronic intracellular bacterial infections such as tuberculosis or brucellosis.

The lymphocyte count may also be elevated in:

  • Smoking (reactive)
  • Hyposplenism (usually following splenectomy)
  • Acute stress response – usually seen in hospital setting, uncommon in community, usually resolves within 24 hours
    • Acute cardiac event
    • Trauma
  • Autoimmune thyroiditis

Chronic lymphocytic leukaemia (CLL) and other lymphoproliferative disorders should be considered in patients with a persistent lymphocytosis.

  • CLL is rarely encountered in people under the age of 40. It is often discovered as an incidental finding on a blood count, but may be associated with lymphadenopathy (disease of the lymph nodes), hepatomegaly (abnormal enlargement of the liver) and splenomegaly (abnormal enlargement of the spleen).

For more information on Lymphocytes or other white blood cells, please visit

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