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 exposures to other substances that are recognised by the body as “non-self” harmful antigens. This test measures the amount of immunoglobulins A, G, and M (IgA, IgG, IgM) in the blood and, in certain circumstances, in cerebrospinal…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 exposures to other substances that are recognised by the body as “non-self” harmful antigens. This test measures the amount of immunoglobulins A, G, and M (IgA, IgG, IgM) in the blood and, in certain circumstances, in cerebrospinal fluid (CSF) or saliva. The first time a person is infected or otherwise exposed to a foreign substance (antigen), their immune system recognises the microorganism or substance as “non-self” and stimulates B-cells (a type of lymphocyte or white blood cell) to produce specific immunoglobulin(s), also called antibodies, that can bind to and neutralise the threat. With subsequent exposures, the immune system “remembers” the antigen that was encountered, which allows for the rapid production of more antibodies by plasma cells (long lived subset of B-cells that are like antibody factories in the bone marrow) and, in the case of microorganisms, 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 M (IgM) – IgM antibodies are produced as a body’s first response to a new infection or to a new “non-self” antigen, providing short-term protection. They increase for several weeks and then decline as IgG production begins. Immunoglobulin G (IgG) – About 70-80% of the immunoglobulins in the blood are IgG. Specific IgG antibodies are produced during an initial infection or other antigen exposure, rising a few weeks after it begins, then decreasing and stabilising. The body retains a catalogue of IgG antibodies that can be rapidly reproduced whenever exposed to the same antigen. IgG antibodies form the basis of long-term protection against microorganisms. In those with a normal immune system, sufficient IgG is produced to prevent re-infection. Vaccinations use this process to prevent infections adding to the catalogue of IgG antibodies, by exposing a person to a killed or weakened, live microorganism or to an antigen that stimulates recognition of the microorganism. IgG is the only immunoglobulin that can pass through the placenta from the mother to the baby. The mother’s IgG antibodies provide protection to the developing baby during pregnancy and then during its first few months of life after birth. There are four subclasses of IgG: IgG1, IgG2, IgG3, and IgG4. Immunoglobulin A (IgA) – IgA comprises about 15% of the total lung and stomach secretions, and breast milk. IgA provides protection against infection in mucosal areas of the body such as the respiratory tract (sinus and lungs) and the gastrointestinal tract (stomach and intestines). When passed from mother to baby during breast-feeding, it helps protect the infant’s gastrointestinal tract. Significant amounts of IgA are not produced by a baby until after 6 months of age so any IgA present in a baby’s blood before then is from the mother’s milk. There are two IgA subclasses: IgA1 and IgA2. Immunoglobulin D (IgD) – This is not usually a secreted antibody, it is the first antibody produced as a receptor on B-cells (B-lymphocytes), it can be abnormally secreted in rare disorders (Hyper IgD Syndrome or HIDS). 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 because the levels are far too low to be detected by the same methods. Quantitative immunoglobulins testing measures 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 immunoglobulins 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 healthcare professional 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. Is any test preparation needed to ensure the quality of the sample?No test preparation is needed. See MoreSee Less
