) in the blood.Many disorders can decrease the number of lymphocytes in the blood, but viral infections (including AIDS) 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 Lymphocytes One of the body's lines of defense ( immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more 
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 Components of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Microorganisms (commonly called germs, such as bacteria, viruses, and fungi) Parasites... read more . 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 Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and can cause acquired immunodeficiency syndrome (AIDS). HIV is transmitted... read more 
(HIV)—the virus that causes AIDS— the influenza virus Influenza (Flu) Influenza (flu) is a viral infection of the lungs and airways with one of the influenza viruses. It causes a fever, runny nose, sore throat, cough, headache, muscle aches (myalgias), and a general... read more , SARS-CoV-2 COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more 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
Causes of acute lymphocytopenia
The number of lymphocytes can temporarily decrease during
Certain viral infections (such as influenza Influenza (Flu) Influenza (flu) is a viral infection of the lungs and airways with one of the influenza viruses. It causes a fever, runny nose, sore throat, cough, headache, muscle aches (myalgias), and a general... read more , hepatitis Overview of Acute Viral Hepatitis Acute viral hepatitis is inflammation of the liver caused by infection with one of the five hepatitis viruses. In most people, the inflammation begins suddenly and lasts only a few weeks. Symptoms... read more , and COVID-19 COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more )
Fasting
Times of severe physical stress
Use of corticosteroids (such as prednisone)
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
Certain autoimmune disorders, such as systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic autoimmune inflammatory connective tissue disorder that can involve joints, kidneys, skin, mucous membranes, and blood vessel walls. Problems in the... read more
(lupus), rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more 
, and myasthenia gravis Myasthenia Gravis Myasthenia gravis is an autoimmune disorder that impairs communication between nerves and muscles, resulting in episodes of muscle weakness. Myasthenia gravis results from malfunction of the... read more Certain chronic infections, such as AIDS Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and can cause acquired immunodeficiency syndrome (AIDS). HIV is transmitted... read more
and miliary tuberculosis Miliary Tuberculosis (TB) Miliary tuberculosis is a potentially life-threatening type of tuberculosis that occurs when a large number of the bacteria travel through the bloodstream and spread throughout the body. Tuberculosis... read more Certain cancers, such as leukemias Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more and lymphomas Overview of Lymphoma Lymphomas are cancers of lymphocytes, which reside in the lymphatic system and in blood-forming organs. Lymphomas are cancers of a specific type of white blood cells known as lymphocytes. These... read more
The number of lymphocytes may be very low permanently in certain hereditary immunodeficiency disorders Overview of Immunodeficiency Disorders Immunodeficiency disorders involve malfunction of the immune system, resulting in infections that develop and recur more frequently, are more severe, and last longer than usual. Immunodeficiency... read more such as DiGeorge syndrome DiGeorge Syndrome DiGeorge syndrome is a congenital immunodeficiency disorder in which the thymus gland is absent or underdeveloped at birth. Children with DiGeorge syndrome are born with several abnormalities... read more , Wiskott-Aldrich syndrome Wiskott-Aldrich Syndrome Wiskott-Aldrich syndrome is a hereditary immunodeficiency disorder characterized by abnormal antibody (immunoglobulin) production, T-cell (lymphocyte) malfunction, a low platelet count, and... read more , severe combined immunodeficiency Severe Combined Immunodeficiency (SCID) Severe combined immunodeficiency is a primary immunodeficiency disorder resulting in low levels of antibodies (immunoglobulins) and low or no T cells (lymphocytes). Most infants with severe... read more , and ataxia-telangiectasia Ataxia-Telangiectasia Ataxia-telangiectasia is a hereditary disorder characterized by incoordination, dilated capillaries, and an immunodeficiency that causes increased susceptibility to infections. In children with... read more 
.
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 Bone Marrow Examination Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Sometimes a sample of bone marrow must be examined to determine... read more ).
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 drug usually begins to resolve within days after a person stops taking the drug. If the lymphocytopenia is the result of AIDS, 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 Stem Cell Transplantation Stem cell transplantation is the removal of stem cells (undifferentiated cells) from a healthy person and their injection into someone who has a serious blood disorder. (See also Overview of... read more .
If an infection develops, a specific antibiotic, antifungal, antiviral, or antiparasitic drug directed against the infective organism is given.
