Lymphocytosis: Definition, Causes, Symptoms, Diagnosis, Treatment, Complications and Prevention

It is a condition that often results after your immune system works to fight an infection or other disease.

There is an increase in white blood cells with this condition. Although it cannot be prevented, lymphocytosis can be treated by taking care of the underlying cause.

What is lymphocytosis?

Lymphocytosis is a higher than an average number of lymphocytes, a subtype of white blood cells in the body. Lymphocytes are part of your immune system and work to fight infection.

Who is most at risk for lymphocytosis?

Anyone can have lymphocytosis.

How common is lymphocytosis?

Lymphocytosis is very common. It is widespread in people who have:

  • A recent infection (most commonly viral).
  • A medical condition that causes long-lasting inflammation, such as arthritis.
  • A reaction to a new medicine.
  • Medical severe illness, such as trauma.
  • Their spleen was removed.
  • Certain types of cancer, such as leukemia or lymphoma.

What Causes Lymphocytosis?

Lymphocytosis is the result of increased numbers of lymphocytes in the blood. Lymphocytes are a type of white blood cell. They play an essential role in your immune system, helping your body fight infection. Many underlying medical conditions can cause lymphocytosis.

High blood levels in lymphocytes indicate that your body is dealing with an infection or other inflammatory condition.


A temporarily high lymphocyte count is an average effect of how your body’s immune system works. Sometimes lymphocyte levels are elevated due to a severe condition, such as leukemia.

Your doctor may order specific diagnostic tests to help identify the cause of your lymphocytosis.

These tests may include other lab tests to rule out infections or difficulties in looking at other tissues in the body, such as a bone marrow biopsy and looking at your blood under a microscope.

What are the symptoms of lymphocytosis?

Lymphocytosis itself does not cause symptoms. However, you may experience symptoms of the underlying cause of lymphocytosis. Depending on the cause, symptoms can range from no signs to severe.

How is lymphocytosis diagnosed?

Your doctor diagnoses lymphocytosis with a blood test called a complete blood count with differential. This test shows an increase in white blood cells, with more than an average number of lymphocytes.

Your doctor may use other diagnostic blood tests, such as a flow cytometry test, to see if the lymphocytes are clonal (seen in a disorder called chronic lymphocytic leukemia).

Tests may also include a bone marrow biopsy to help determine the root cause of the lymphocytosis. Doctors rely on your medical history, current symptoms, medication list, and physical exam to help determine the underlying cause of lymphocytosis.

How is lymphocytosis treated?

Doctors treat lymphocytosis by working to resolve its underlying cause. For most people, lymphocytosis clears up as the underlying condition improves.

What complications are associated with lymphocytosis?

Lymphocytosis tells your doctor that you have or have had an infection or illness. In many cases, lymphocytosis means that your body has been fighting a viral infection.

In some cases, lymphocytosis is one of the first signs of certain blood cancers, including chronic lymphocytic leukemia (CLL), the most common type of leukemia in adults.

More tests are usually needed to rule out other medical conditions and make a firm diagnosis of the cause of lymphocytosis.

Can lymphocytosis be prevented?

There is no way to prevent lymphocytosis. You can reduce your risk of viral infection by:

  • Wash your hands frequently and often with soap and water.
  • Avoid contact with sick people.
  • Avoid sharing personal items with sick people.
  • Disinfection of surfaces and articles of everyday use.

What is the result after lymphocytosis treatment?

Lymphocytosis usually goes away after treatment for the condition or disease that caused the body to make extra white blood cells.

When should I call my doctor?

Contact your doctor if you have a persistent infection or experience chronic (ongoing) symptoms or symptoms that get worse over time. Your doctor can determine if you have lymphocytosis during a complete medical exam.