Lymphocytosis (high lymphocyte count) is often a sign that your immune system is fighting an intruder. Lymphocytes are a type of white blood cell. Viral infections often cause lymphocytosis. Less frequently, a high count is a sign of blood cancer. Lymphocytosis may go away on its own. But you may need treatment for the condition that causes it.
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Lymphocytosis — or high lymphocyte count — means there’s a higher-than-normal number of lymphocytes in your blood. Lymphocytes are a type of white blood cell. They consist of B cells, T cells and NK cells, which help your immune system fight cancer and infections.
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A routine blood test may detect an increase in your white blood cells called leukocytosis. The differential that can be ordered with your routine blood counts will break down the types of white blood cells, including the lymphocytes.
An increase in lymphocytes typically means they’re working to get rid of an invader, like an infection that can make you sick. Healthcare providers may call this reactive lymphocytosis. Less frequently, a high lymphocyte count is a sign of cancer in your blood or lymphatic system. The lymphatic system is a way that immune cells travel through your body.
Healthcare providers measure these white blood cells by the number of lymphocytes in 1 microliter of blood. The normal range for adults is between 1,000 and 4,800 lymphocytes in every microliter of blood. The normal range for children is between 3,000 and 9,500 per microliter. It’s normal for children to have higher levels than adults.
A high lymphocyte count itself doesn’t cause symptoms. But an infection or other conditions that cause high lymphocyte counts can cause symptoms like:
Infections, blood cancers and other issues may increase the number of lymphocytes in your blood.
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Viral infections are the most common cause. But some bacterial infections may also increase your lymphocyte count. Examples include:
Sometimes, lymphocytosis is one of the first signs of certain blood cancers or cancers of your lymphatic system. Cancers associated with high lymphocyte counts include:
Other medical conditions, lifestyle habits and even stress can cause lymphocytosis. For example, some autoimmune diseases or having your spleen removed can increase your lymphocyte count. Other examples are:
Healthcare providers do blood tests to check on your lymphocytes, including:
Your provider may do follow-up tests to see if your lymphocyte levels drop. They may do other tests if your lymphocyte levels stay high. They may also refer you to a hematologist for more tests.
You may have lymphocytosis and not need treatment. For example, your provider may decide your immune system is fighting off an infection.
You may need treatment for the infection if your symptoms don’t get better and you still have high lymphocyte levels. For example, your provider may prescribe an antibiotic to treat a bacterial infection.
If tests detect cancer, your provider will refer you to a hematologist/oncologist for treatment.
Contact a healthcare provider if you have symptoms like a fever that doesn’t go away or swollen lymph nodes. Bacterial and viral infections often cause these symptoms.
It can, but not often. A condition called monoclonal B-cell lymphocytosis (MBL) can lead to chronic lymphocytic leukemia (CLL). Monoclonal refers to a B-lymphocyte that makes clones or identical copies. High numbers of identical B-lymphocytes increases your risk for CLL. Your risk increases if you have a family history of this blood cancer.
Don’t be alarmed if a blood test shows you have lymphocytosis. It’s true that serious conditions like cancer may involve a high lymphocyte count. But 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.
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Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.
Cleveland Clinic’s health articles are based on evidence-backed information and review by medical professionals to ensure accuracy, reliability and up-to-date clinical standards.
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