Patient education: Lymphocytosis (The Basics)

What is lymphocytosis? — 

This is when the blood has too many "lymphocytes." Lymphocytes are a type of white blood cell. They are part of body's lymphatic system. The lymphatic system is made up of organs all over the body that make and store cells that fight infection (figure 1).

It is normal for the number of lymphocytes to increase when your body is fighting an infection. Usually, the lymphocyte count goes back down again once you are better. Sometimes, other health problems or medicines can also cause lymphocytosis.

What causes lymphocytosis? — 

Lots of different things can cause it. They include:

●Many viral infections, and some infections caused by bacteria or other germs

●An allergic reaction to a medicine

●An injury

●A medical event like a heart attack or seizure

●Surgery to remove the spleen

●Some "autoimmune" conditions, like rheumatoid arthritis

●Hyperthyroidism

●Certain blood cancers, such as some types of leukemia and lymphoma

Is there a test for lymphocytosis? — 

Yes. A blood test called a "complete blood count with white blood cell differential," or "CBC with diff," looks at all of the different types of white blood cells in your blood. It can show if you have lymphocytosis. The important number is the "lymphocyte count," not the percentage.

Your doctor or nurse might order other tests, too. This depends on your age, other symptoms, and individual situation. Some of the things doctors use to find the cause of lymphocytosis include:

●CBC results – Sometimes, there are other clues from the CBC, such as the numbers of other blood cells.

●Blood smear – This lets the doctor look at your blood cells under a microscope. The size, shape, and appearance of your lymphocytes can give information about your health.

●Other lab tests – Sometimes, other lab tests can be helpful. These might include blood tests to check your kidneys or liver, or tests to look for inflammation in your body.

If the cause is not clear and your lymphocyte level does not return to normal, doctors can do other tests to check for more serious causes. These can include tests to analyze your blood cells, genetic testing, and other tests on your blood, bone marrow, or lymph nodes.

How is lymphocytosis treated? — 

The treatment depends on what caused your lymphocytosis. For example, some infections and other problems need specific treatment. If your body is fighting an infection, your doctor will probably check your lymphocyte level again in a few weeks to see if it has returned to normal.

If tests find that you have a more serious health condition, your doctor will talk to you about your treatment options.

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