Lymphocytes: What Normal, Low and High Levels Mean

Medically Reviewed By William C. Lloyd III, MD, FACS
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What are lymphocytes?

Lymphocytes are a type of white blood cell, which are part of the body’s immune system. There are three types of lymphocytes and they make up from 20 to 40% of the total blood volume. Blood tests indicate how many lymphocytes are circulating through the body.

Too many lymphocytes in the blood is called lymphocytosis. The most common cause of excessive lymphocytes is an infection, but lymphocyte levels can also rise if there are other conditions, such as leukemia.

Too few lymphocytes is called lymphocytopenia or lymphopenia. Although a viral infection can cause it, other factors, such as fasting or severe physical stress can reduce lymphocyte numbers as well.

Lymphocytes develop in the bone marrow, the soft spongy tissue inside bones, and in the thymus. The thymus is a small organ behind the breast bone, just above the heart.

Treatment for high or low levels of lymphocytes in the blood depends on the cause. Promptly treating infections will help prevent serious complications. Treatment of lymphoma and other types of cancer in the early stages is often successful.

If a blood test shows your lymphocyte level is out of the normal range, your healthcare professional will discuss next steps with you, which may include additional tests to determine an underlying cause and, if necessary, guide treatment.

What are the different types of lymphocytes?

There are three types of lymphocytes. The two main types are B cells and T cells. The third is the NK, or natural killer cell. This is a brief explanation of their function:

  • B cell lymphocytes are produced in the bone marrow. They make antibodies against foreign antigens like bacteria.

  • T cell lymphocytes are either helper cells or killer cells. The helper T cells help the B cells make antibodies. Killer T cells directly kill antigens, usually viruses. T cells may also kill cancer cells.

  • NK cells kill antigens, particular cancer cells.

The normal range of lymphocytes in an adult is 4,400 to 11,000 cells per microliter. Less than that is lymphocytopenia or lymphopenia. More than that might indicate lymphocytosis.

What are the symptoms of low or high levels of lymphocytes?

There are several potential causes for lymphopenia and lymphocytosis.

Symptoms of lymphopenia 

The most common symptoms of lymphopenia/lymphocytopenia are:

  • Enlarged lymph nodes, usually noticeable in the neck and groin

  • Enlarged spleen, which the doctor or nurse practitioner can feel during a physical exam

  • Rash

  • Signs of a viral infection, such as fever, but specific symptoms depend on the type of infection

  • Sore joints

Symptoms of lymphocytosis

Lymphocytosis does not usually cause symptoms. Medical professionals most often discover it during blood tests for a routine doctor’s appointment or a diagnostic work up for another condition.

What causes low or high lymphocytes?

There are several potential causes for lymphopenia and lymphocytosis.

Common causes of lymphopenia

The most common causes of lymphopenia/lymphocytopenia are:

Common causes of lymphocytosis

The most common lymphocytosis causes are:

How do doctors diagnose the cause of low or high levels of lymphocytes?

Once a blood test reveals an abnormal number of lymphocytes in the blood, the doctor needs to do more investigations to determine why.

Your doctor might ask questions like:

  • Have you been sick or exposed to any contagious illnesses recently?

  • What symptoms are you experiencing, if any?

  • How long have you had these symptoms?

Tests will depend on what the doctor suspects. You may need more blood tests as well as imaging (X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) and ultrasounds).

Other tests could include swabs of discharge and biopsies.

What are the treatments for low or high lymphocyte counts?

Treating lymphocyte abnormalities depends on the cause. For example, medical professionals treat infections with antimicrobials and cancers with chemotherapy, radiation therapy, surgery, or targeted therapies. Lymphocyte counts should return to the normal range after treatment.

Sometimes, treatment is as simple as discontinuing a medication that is causing lymphocytopenia. Other times, treatment is lifelong, especially if the cause is a chronic illness like lupus.

If the lymphocyte count is too low, doctors may administer gamma globulin, by intravenous (IV), to help boost the body’s immunity against disease. Gamma globulin contains antibodies. This will help reduce the risk of infections.

What are the potential complications of low or high lymphocyte counts?

Since lymphocytes are part of the immune system, too few in the blood system means that there is a higher-than-average risk of infection. In cases of lymphocytosis, an excess number of circulating lymphocytes could lead to rupture of the spleen, reduced levels of gamma globulin to fight infection, and leukostasis (sluggish blood flow), which could cause stroke, myocardial infarction, and loss of vision.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Dec 15
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