At a Glance
Why Get Tested?
To detect and/or monitor increased or decreased levels of one or more of the immunoglobulin types (IgG, IgA, and IgM) that are used to evaluate a person's immune system status
When to Get Tested?
When you have recurrent infections and/or chronic diarrhea; when your doctor suspects an immunoglobulin deficiency; periodically to monitor a condition that affects immunoglobulin levels that may be genetic or acquired (HIV/AIDS, Multiple Myeloma)
A blood sample drawn from a vein in your arm; sometimes a cerebrospinal fluid (CSF) or saliva sample
Test Preparation Needed?
The Test Sample
What is being tested?
This test measures the amount of immunoglobulins A, G, and M in the blood and, in certain circumstances, in cerebrospinal fluid (CSF) or saliva. There are numerous conditions and diseases that can cause increased or decreased production of immunoglobulins (Igs).
Immunoglobulins play a key role in the body's immune system. They are proteins produced by specific immune cells called plasma cells in response to bacteria, viruses, and other microorganisms as well as substances that are recognized as "non-self" and harmful antigens. The first time a person is infected or otherwise exposed to a foreign substance (antigen), their immune system recognizes the microorganism or substance as "non-self" and stimulates plasma cells to produce specific immunoglobulin(s) or antibodies that can bind to and neutralize the threat. With subsequent exposures, the immune system "remembers" the antigen that was encountered, which allows for the rapid production of more antibodies and helps prevent re-infection.
There are five classes of immunoglobulins and several subclasses. Each class represents a group of antibodies and has a slightly different role. Classes of immunoglobulins include:
- Immunoglobulin G (IgG) – About 70-80% of the immunoglobulin in the blood is IgG. IgG antibodies form the basis of long-term protection against microorganisms. Specific IgG antibodies are produced during an initial infection or exposure, rising a few weeks after it begins, then decreasing and stabilizing. The body retains a catalog of IgG antibodies that can be rapidly reproduced whenever exposed to the same antigen. In those with a normal immune system, sufficient IgG is produced to prevent re-infection. Vaccinations use this process to prevent initial infections and add to the catalog of IgG antibodies, by exposing a person to a weakened, live microorganism or to an antigen that stimulates recognition of the microorganism. IgG is the only immunoglobulin that can pass through the placenta. The mother's IgG antibodies provide protection to the fetus during pregnancy and to the baby during its first few months of life. There are four subclasses of IgG: IgG1, IgG2, IgG3, and IgG4.
- Immunoglobulin A (IgA) – IgA comprises about 15% of the total serum immunoglobulins but is also found in saliva, tears, respiratory and gastric secretions, and breast milk. IgA provides protection against infection in mucosal areas of the body such as the respiratory tract and the gastrointestinal tract. When passed from mother to baby during breast-feeding, it helps protect the infant's gastrointestinal tract. Significant amounts of IgA are not present until after 6 months of age. There are two IgA subclasses: IgA1 and IgA2.
- Immunoglobulin M (IgM) – IgM antibodies are produced as a body's first response to a new infection, providing short-term protection. They increase for several weeks and then decline as IgG production begins. IgM can be produced by a fetus but, due to the size of the IgM molecule, it does not pass through the placenta. IgM antibodies in a newborn can indicate an infection that began during pregnancy.
- Immunoglobulin D (IgD) – the role of IgD is not well defined and IgD is not routinely measured.
- Immunoglobulin E (IgE) – IgE is associated with allergies, allergic diseases, and with parasitic infections. It is almost always measured as part of an allergy testing blood panel, but typically is not included as part of a quantitative immunoglobulins test.
Quantitative immunoglobulin tests measure the total amount of each primary immunoglobulin class, IgA, IgM, and IgG, without distinguishing between subclasses. Separate testing can be performed to measure immunoglobulin subclasses and/or to detect and measure specific antibodies.
A variety of conditions can cause an increase (hypergammaglobulinemia) or decrease (hypogammaglobulinemia) in the production of immunoglobulins. Some cause an excess or deficiency of all classes of Igs while others affect only one class. Some of the conditions are passed from one generation to the next (inherited) and others are acquired.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. When required, a sample of cerebrospinal fluid (CSF) is collected by a doctor from the lower back using a procedure called a lumbar puncture or spinal tap. Saliva or other fluids are collected in a container provided by the laboratory.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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