What Level of Lymphocytes Is Dangerous? (2024)

High or low lymphocyte levels can indicate a problem with your immune system. Lymphocytes are a type of white blood cell. They play a key role in your immune system by helping your body fight infection and disease.

Normal lymphocyte counts are generally between 1,000 and 4,800 cells per microliter of blood in adults and 3,000 to 9,500 cells per microliter in children.

Your level of lymphocytes can be too low (lymphopenia) or too high (lymphocytosis). These readings are common on blood tests but may require further testing as directed by your healthcare provider.

Normal Lymphocyte Counts

Lymphocytes are measured in cells per microliter of blood (cells/mL). The total lymphocyte count generally goes down throughout a person's life.

Normal lymphocyte counts are as follows:

• Adults: 1,000 cells/mL to 4,800 cells/mL
• Children: 3,000 cells/mL to 9,500 cells/mL

Levels outside the normal range can occur temporarily or indicate a chronic condition. Having too many or too few lymphocytes in your blood can be a sign of infection, autoimmune diseases, and possibly even cancer. Certain medical treatments can also alter your lymphocyte levels temporarily.

Some diseases can cause both lymphocytosis and lymphopenia. For instance, an infection will typically cause lymphocyte counts to increase, but recurrent or severe infections may also cause lymphocyte numbers to plummet.

In other instances, a disease may cause one type of lymphocyte to increase and another type to drop.

High Levels (Lymphocytosis)

Having too many lymphocytes in your blood is called lymphocytosis—an indication that the immune system has been activated in response to a disease or medical condition. Lymphocytosis is defined as a lymphocyte count of:

• Young children: greater than 8,000 cells/mL
• Adults and teenagers: greater than 4,000 cells/mL

High lymphocyte levels are commonly caused by transient (temporary) viral infections, such as those with the Epstein-Barr virus or cytomegalovirus (both causes of infectious mononucleosis, or mono).

Lymphocytosis can also persist with chronic (long-term) infections such as hepatitis B or human immunodeficiency virus (HIV).

It's common to see high lymphocyte levels on a blood test. If that's the case, it's essential to establish the cause and rule out serious conditions like cancer, often with additional tests and examinations.

Lymphocytosis can indicate cancer of the blood or lymphatic system, such as chronic lymphocytic leukemia (a slow-growing type of blood cancer).

Other possible causes of lymphocytosis include:

• Acute lymphoblastic leukemia (a type of blood cancer)
  
• Hepatitis A (a viral infection affecting the liver)
• Hepatitis C (a viral infection affecting the liver)
• Hypothyroidism (low thyroid function)
• Lymphomas (cancers of the lymphatic system)
• Mononucleosis (also known as mono and most commonly caused by the Epstein-Barr virus)
• Pertussis ("whooping cough")
• Syphilis (a sexually transmitted bacterial infection)
  
• Toxoplasmosis (a parasitic infection)
• Tuberculosis (a bacterial infection mainly affecting the lungs)

Lymphocytosis can lead to lymphadenopathy (swollen lymph nodes) and splenomegaly (an enlarged spleen). Splenomegaly can cause dull pain in the upper right portion of the body. Other symptoms may develop depending on the underlying cause.

Low Levels (Lymphopenia)

Having too few lymphocytes is called lymphopenia—an indication that lymphocytes are either being depleted or are not being produced in ample quantities.

Lymphopenia is generally defined by a lymphocyte count of less than 1,000 cells/mL.

Sometimes, lymphopenia can be diagnosed at higher counts as well. A healthcare provider may determine an adult has lymphopenia if they have less than 1,500 cells/mL.

A child age 6 or younger can be diagnosed with lymphopenia if they have less than 2,000 cells/mL.

Low lymphocyte levels may be due to autoimmune diseases, infections, or certain medical treatments. Rare genetic disorders may also interfere with the normal production of lymphocytes.

Possible causes of lymphopenia include:

• Aplastic anemia (a reduction of red blood cells due to bone marrow failure)
• Chemotherapy cancer treatment
• COVID-19
• Hodgkin lymphoma (one of two major types of lymphoma)
• Immunosuppressants (drugs commonly used to treat autoimmune diseases and prevent organ transplant rejection)
• Lupus (a type of autoimmune disease affecting multiple organs)
• Malnutrition
• Radiation therapy
• Severe combined immunodeficiency (a rare inherited disorder characterized by a low immune response)
• Tuberculosis
• Typhoid fever (a tropical bacterial infection)

Treatment

Lymphocytosis and lymphopenia are both treated by addressing the underlying cause. Possible types of treatments include:

• Antibiotics for bacterial infections
• Antiviral medications
• Chemotherapy for cancer treatment
• Bone marrow or stem cell transplant
• Immunoglobulin (an immune system-boosting medication)

Some causes of lymphocytosis or lymphopenia resolve on their own with time, and no treatment is needed.

Testing

Blood tests are routinely performed whenever you have signs of an infection and other illnesses. These include tests that measure how many lymphocytes you have in your blood.

The tests are easy to perform and only require a simple blood draw, typically from a vein in your arm.

They include:

• Complete blood count with differential (CBC w/ diff): Can reveal the percentage of each type of white blood cell in your blood, including lymphocytes. It also measures the amount of red blood cells, platelets, and hemoglobin.
• Flow cytometry: Can identify the individual cells in your blood, including lymphocytes. Your blood is suspended in a fluid and passed through a laser-generating instrument. The light produced from the laser scatters the cells so they can be counted and analyzed.
• B and T cell screen: Counts B cells and T cells in a sample of blood. It can provide information about your immune system and whether a disease is cancerous or not. It can also help evaluate ongoing treatments.

Summary

Lymphocytes are a type of white blood cell. They are produced in the bone marrow and move throughout the lymphatic system to help fight infection and diseases.

A normal lymphocyte count varies by age—the older you are, the lower it typically is.

Adults usually have a lymphocyte count between 1,000 cells/mL and 4,800 cells/mL, but it's common to get a blood test result outside of that range. Your healthcare provider will likely suggest further testing to determine the cause.

Having too many lymphocytes (lymphocytosis) or too few lymphocytes (lymphopenia) is commonly a sign of an infection, but may be due to an autoimmune disease, genetic disorder, or cancer.

Certain medical treatments can also affect lymphocyte counts. Treatment focuses on the underlying cause.