Immunoglobulins (also called immune system in response to bacteria, viruses, or other foreign substances (such as fungus and animal dander). Antibodies attach to the foreign substances, causing them to be destroyed by other immune system cells.

Antibodies are usually specific to each type of foreign substance. For example, antibodies produced in response to a tuberculosis infection attach only to tuberculosis bacteria. Antibodies also play a role in allergic reactions. Occasionally, a person may produce antibodies against tissues in his or her body (called autoimmune disease).

A person whose immune system produces low levels of antibodies may be at an increased risk of developing repeated infections. A person may be born with an immune system that produces low levels of antibodies, or the immune system may produce low levels of antibodies in response to certain diseases (such as cancer).

The five major types of antibodies are:

• IgA. IgA antibodies are found mainly in areas of the body such as the nose, breathing passages, digestive tract, ears, eyes, and vagina. IgA antibodies protect body surfaces that are exposed to the outside from foreign organisms and substances. This type of antibody is also found in saliva and tears. About 10% to 15% of the antibodies usually present in the body are IgA antibodies. A small percentage of people do not make IgA antibodies.
• IgG. IgG antibodies are found in all body fluids. They are the smallest but most abundant of the antibodies, normally comprising about 75% to 80% of all the antibodies in the body. IgG antibodies are considered the most important antibodies for fighting bacterial and viral infections. IgG antibodies are the only type of antibody that can cross the placenta. Therefore, the IgG antibodies of a pregnant woman can also help protect her fetus.
• IgM. IgM antibodies are the largest type of antibody. They are found in blood and lymph fluid and are the first type of antibody produced in response to an infection. They also cause other immune system cells to produce compounds that can destroy invading cells. IgM antibodies normally comprise about 5% to 10% of all the antibodies in the body.
• IgD. IgD antibodies are found in small amounts in the tissues that line cavities inside the body. The function of IgD antibodies is not well understood. They appear to play a role in allergic reactions to some substances such as milk, some medications, and some poisons.
• IgE. IgE antibodies are found in the lungs, skin, and mucous membranes. They help protect the body against foreign substances such as pollen, fungus spores, and animal dander. IgE antibody levels are often high in people with allergies.

The relative numbers of each type of antibody can give information about the cause of a medical problem.

Immunoglobulins
Results

Children have slightly different immunoglobulin values than adults.

Normal

Normal values may vary from lab to lab.

Greater than normal values may mean

• IgA. High levels of IgA may indicate multiple myeloma. Levels of IgA also increase in some autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus (SLE), and in liver diseases, such as cirrhosis and long-term (chronic) hepatitis.
• IgG. High levels of IgG may indicate a long-term (chronic) infection, such as AIDS. Levels of IgG also increase in multiple myeloma, long-term hepatitis, multiple sclerosis (MS), and some autoimmune diseases. In multiple myeloma, tumor cells produce only one type of IgG antibody (monoclonal). The other conditions cause an increase in many types of IgG antibodies (polyclonal).
• IgM. High levels of IgM can indicate macroglobulinemia, early viral hepatitis, mononucleosis, rheumatoid arthritis, kidney damage (nephrotic syndrome), or a parasite infection. Because IgM antibodies are the type that form when an infection occurs for the first time, high levels of IgM can indicate a new infection is present. High levels of IgM in a newborn usually indicate that the baby has an infection.
• IgD. The role of IgD in the immune system is not well understood. A high level of IgD may indicate multiple myeloma.
• IgE. A high level of IgE can indicate a parasite infection. Also, high levels of IgE are found in people who have allergic reactions,asthma, atopic dermatitis, some types of cancer, and certain autoimmune diseases.

Lower than normal values may mean

• IgA. Low levels of IgA occur in some types of leukemia, kidney damage (nephrotic syndrome), a problem with the intestines (enteropathy), and a rare inherited disease that affects muscle coordination (ataxia-telangiectasia). Some people are born with low levels of IgA antibodies, which increases their chances of developing an autoimmune disease.
• IgG. Low levels of IgG occur in macroglobulinemia. In this disease, the high levels of IgM antibodies suppress the growth of cells that produce IgG. Other conditions that can result in low levels of IgG include some types of leukemia and a type of kidney damage (nephrotic syndrome). Rarely, some people are born with a deficiency of IgG antibodies.
• IgM. Low levels of IgM occur in multiple myeloma and some types of leukemia.
• IgE. Low levels of IgE can occur in a rare inherited disease that affects muscle coordination (ataxia-telangiectasia).