ByDavid C. Dale, MD, University of Washington
Reviewed/Revised Apr 2023

Lymphocytopenia is an abnormally low number of lymphocytes (a type of white blood cell) in the blood.

  • Many disorders can decrease the number of lymphocytes in the blood, but viral infections (including HIV infection) and undernutrition are the most common.

  • People may have no symptoms, or they may have fever and other symptoms of an infection.

  • A blood sample is used to make the diagnosis of lymphocytopenia, but a sample of bone marrow or lymph node may be needed to determine the cause.

  • Doctors treat the cause of lymphocytopenia.

  • Some people are given gamma globulin, and some benefit from stem cell transplantation.

Lymphocytes are a type of white blood cell that plays several roles in the immune system, including protection against bacteria, viruses, fungi, and parasites. Lymphocytes usually constitute 20 to 40% of all white blood cells in the bloodstream. The lymphocyte count is normally above 1,500 cells per microliter of blood (1.5 × 109 per liter) in adults and above 3,000 cells per microliter of blood (3 × 109 per liter) in children. A reduction in the number of lymphocytes may not cause a noticeable decrease in the total number of white blood cells.

Types of lymphocytes

There are three types of lymphocytes:

  • B lymphocytes (B cells)

  • T lymphocytes (T cells)

  • Natural killer cells (NK cells)

All three types have important functions in the immune system. Too few B cells can lead to a decrease in the number of plasma cells, which produce antibodies. Decreased antibody production can cause an increase in bacterial infections.

People who have too few T cells or too few NK cells have problems controlling certain infections, especially viral, fungal, and parasitic infections. Severe lymphocyte deficiencies can result in uncontrolled infections that can be fatal.

Causes of Lymphocytopenia

Various disorders and conditions, including infection with viruses such as human immunodeficiency virus (HIV)—the virus that causes AIDS— the influenza virus, and SARS-CoV-2 (the virus that causes COVID-19) can decrease the number of lymphocytes in the blood. Lymphocytopenia can be

  • Acute: Occurring briefly during certain conditions and then usually resolving

  • Chronic: Occurring for a longer period because of long-lasting disorders

Did You Know...

  • AIDS and undernutrition are the most common causes of chronic lymphocytopenia.

Causes of acute lymphocytopenia

The number of lymphocytes can temporarily decrease during

  • Certain viral infections (such as influenza, hepatitis, and COVID-19)

  • Fasting

  • Times of severe physical stress

  • Chemotherapy and/or radiation therapy for cancer

Causes of chronic lymphocytopenia

The number of lymphocytes can remain low for a long time when people have

The number of lymphocytes may be very low permanently in certain hereditary immunodeficiency disorders such as DiGeorge syndrome, Wiskott-Aldrich syndrome, severe combined immunodeficiency, ataxia-telangiectasia, and WHIMs (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome.

Symptoms of Lymphocytopenia

Mild lymphocytopenia may cause no symptoms. Sometimes, symptoms of the condition that caused lymphocytopenia may be present. For example, people may have

  • Enlarged lymph nodes and an enlarged spleen, suggesting cancer or HIV infection

  • Cough, runny nose, and fever, suggesting a respiratory viral infection

  • Small tonsils or lymph nodes, suggesting an inherited immune system disorder

  • Painful swollen joints and a rash, suggesting rheumatoid arthritis or systemic lupus erythematosus

Drastically reduced numbers of lymphocytes lead to repeated infections with bacteria, viruses, fungi, and parasites and the symptoms of those infections, which vary widely according to the site of infection and the specific microorganism.

Diagnosis of Lymphocytopenia

  • Complete blood count

Mild lymphocytopenia is usually diagnosed by chance when a complete blood count is done for other reasons. Complete blood count testing also is done in people with recurrent or severe infections and in people with infections caused by organisms that do not usually cause infections. Such testing may show severe lymphocytopenia as an explanation for why the person has developed recurrent or unusual infections.

When the numbers of lymphocytes are drastically reduced, doctors usually do a blood test for human immunodeficiency virus (HIV) and other infections and sometimes take a sample of bone marrow to examine under a microscope (bone marrow examination).

The number of specific types of lymphocytes (T cells, B cells, and NK cells) in the blood can also be determined. A decrease in certain types of lymphocytes may help doctors diagnose some disorders, such as AIDS or certain hereditary immunodeficiency disorders.

Treatment of Lymphocytopenia

  • Treatment of the cause

Treatment of lymphocytopenia depends mainly on the cause. Lymphocytopenia caused by a medication usually begins to resolve within days after a person stops taking the medication. If the lymphocytopenia is the result of HIV infection, combination therapy with at least three antiviral drugs of different classes can increase the number of T cells and lengthen survival.

Gamma globulin (a substance rich in antibodies) may be given to help prevent infections in people with too few B cells (who therefore have a deficiency of antibody production).

People with a hereditary immunodeficiency disorder may benefit from stem cell transplantation.

If an infection develops, a specific antibiotic, antifungal, antiviral, or antiparasitic drug directed against the infective organism is given.

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