What is it?

Lymphocytosis, or a high lymphocyte count, is an increase in white blood cells called lymphocytes. Lymphocytes help fight off diseases, so it's normal to see a temporary increase after infection. The exact thresholds for lymphocytosis can vary slightly from one lab to another.

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Signs & symptoms

Lymphocytosis doesn’t cause symptoms. However, symptoms might be connected to the cause of the spike in white blood cell count. Depending on the cause, symptoms may range from no signs to severe. Often, people learn of a high lymphocyte count incidentally after taking a blood test to check for other conditions.


A blood test called a complete blood count (CBC) with differential usually diagnoses lymphocytosis. This test shows if there is a higher-than-normal amount of lymphocytes. Another flow cytometry test might check if the lymphocytes are clonal (seen in cancers like chronic lymphocytic leukemia). Testing may also include a bone marrow biopsy to help determine the root cause of lymphocytosis.


Lymphocytosis treatment involves resolving what is causing the high lymphocyte count. Receiving treatment for the underlying cause can help restore lymphocyte levels to normal.

☝️ This is not a substitute for professional medical advice. Please consult with your physician before making any medical decision.

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