Lymphocytosis often results from your immune system fighting off an infection or other disease. White blood cells called lymphocytes increase with these conditions. Lymphocytosis isn’t preventable, but it can be treated by addressing what’s causing your temporary high lymphocyte count.
Lymphocytosis — or high lymphocyte count — means having a higher-than-normal amount of lymphocytes in your blood. Lymphocytes are a type of white blood cell. They play an essential role in your immune system, helping your body fight infections.
Having a temporarily high lymphocyte count usually means that your body is working as it should to protect you from germs that make you sick. Less often, lymphocytosis is a sign of a more serious condition.
For adults, a high lymphocyte count means more than 4,000 lymphocytes in 1 microliter of blood.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Lymphocytosis is very common, especially in people who have:
High lymphocyte blood levels often indicate your body is dealing with an infection or other inflammatory condition. A spike in your lymphocytes typically means that these white blood cells are springing into action to rid your body of an invader that can make you sick. Sometimes a serious condition, like cancers that affect your blood or lymphatic system, may cause elevated lymphocyte levels.
Many medical conditions can cause lymphocytosis:
Lymphocytosis doesn’t cause symptoms. However, you may experience symptoms from what’s causing the spike in your white blood cell count. For instance, the lymph nodes in your neck may feel swollen due to an infection, which may be causing lymphocytosis. Depending on the cause, symptoms may range from no symptoms to severe.
Often, people learn of a high lymphocyte count incidentally after taking a blood test to check for other conditions.
Providers rely on your medical history, current symptoms, medication list, and a physical exam to help determine what’s causing lymphocytosis. They may ask questions about your habits and lifestyle to see if you’re at high-risk for certain infections, such as sexually transmitted infections (STIs). They may perform a blood test to check your lymphocyte count.
If your levels are high, your provider may retest later to see if the spike is temporary. If your levels remain high and your provider is unsure why, they may order additional tests. You may be referred to a blood specialist called a hematologist for a diagnosis.
Your provider may order a blood test called a complete blood count (CBC) with differential. This test shows if you have a higher-than-normal amount of lymphocytes. They may order a flow cytometry test to see 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’s causing the high lymphocyte count. If your body is producing white blood cells to fight a germ, you may not need treatment. In time, your immune system can usually take care of the issue. If the spike in white blood cells is a sign of cancer, you can discuss treatment options with your provider.
Receiving treatment for the underlying cause can help restore your lymphocyte levels to normal.
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. Further tests are usually necessary to rule out other medical conditions and make a firm diagnosis of the cause of lymphocytosis.
Lymphocytosis isn't preventable. You can reduce your risk by taking steps to keep from getting sick:
Lymphocytosis usually goes away after treatment for the condition or disease that caused your body to produce extra white blood cells.
Contact your provider 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 examination.
It can, but this is rare. Sometimes monoclonal B-cell lymphocytosis (MBL) progresses to a specific leukemia called chronic lymphocytic leukemia (CLL). A B-cell is a particular type of lymphocyte. With MBL, you have a higher-than-normal amount of clonal B-cells in your blood.
A note from Cleveland Clinic
Don’t be alarmed if you have lymphocytosis. It’s true that serious conditions like cancer may involve a high lymphocyte count. There’s a much greater chance that an infection is to blame. Your lymphocyte levels will likely return to normal once your immune system has cleared the infection. If your levels remain high, your provider can recommend tests and treatments to address the underlying cause.
Last reviewed by a Cleveland Clinic medical professional on 05/16/2022.
Learn more about our editorial process.