Immunoglobulins (IgA, IgG, IgM Blood Test)

A test for immunoglobulins (Igs) is used to detect an excess or deficiency in the three major classes of immunoglobulins (IgG, IgA, and IgM). It gives important information about the health of an individual’s immune system and is used to help diagnose various conditions and diseases that affect the levels of one or more of these Ig classes.

In general, immunoglobulin disorders can be classified as:

• Immunoglobulin excess
  • Polyclonal—an Ig excess in any or all immunoglobulin classes from many different immune (plasma) cells
  • Monoclonal—the excess immunoglobulins are from the clones of one plasma cell

• Immunoglobulin deficiency
  • Secondary (acquired)—the most common Ig deficiencies are caused by an underlying condition or contributing factor
  • Primary (inherited)—these are rare disorders in which the body is not able to produce one or more classes of immunoglobulins

This test may be ordered along with others, such as a serum and/or urine protein electrophoresis, to help diagnose and monitor conditions associated with abnormal or excessive immunoglobulin production. When this is the case, a urine sample may be collected in addition to blood.

If an excessive amount of one of the immunoglobulin types is present, further testing by immunofixation can be done to determine if the immunoglobulin comes from clones of an abnormal plasma cell (monoclonal gammopathy). Monoclonal gammopathies are seen with multiple myeloma, a malignancy of plasma cells. Serum free light chain testing may also be performed.

This test is ordered when a person has symptoms of an immunoglobulin deficiency such as recurrent infections, especially of the respiratory tract (sinus, lungs) or digestive system (stomach, intestines), and/or chronic diarrhea.

Immunoglobulins testing may also be ordered when a person has signs of chronic inflammation or chronic infection and when a health care practitioner suspects excess or abnormal immunoglobulin production. The test may be ordered periodically to monitor the course of a person’s condition.

This test may also be performed on cerebrospinal fluid (CSF) whenever a health practitioner suspects that a condition affecting the central nervous system may be associated with excess immunoglobulin production.

The results of the tests for IgG, IgA, and IgM levels are usually evaluated together. Abnormal test results typically indicate that there is something affecting the immune system and suggest the need for further testing. Immunoglobulins testing is not diagnostic but can be a strong indicator of a disease or condition. There are a number of conditions that are associated with increased and decreased immunoglobulins.

High levels
Increased polyclonal immunoglobulins may be seen with a variety of conditions.

Monoclonal immunoglobulins are seen in blood cell tumors that involve lymphocytes or plasma cells. In these disorders, there is typically a marked increase in one class of immunoglobulin and a decrease in the other two classes. Although affected people may have an increase in total immunoglobulins, they are actually immunocompromised because most of the immunoglobulins produced are abnormal and do not contribute to the immune response.

The following table lists some examples of conditions that may cause increased immunoglobulins:

Low levels
The most common causes of decreased immunoglobulins are acquired underlying (secondary) conditions that either affect the body’s ability to produce immunoglobulins or that increase the loss of protein from the body. Deficiencies may also be due to drugs such as immunosuppressants, corticosteroids, phenytoin, and carbamazepine or due to toxins.

The table below lists some of the common causes of low levels:

Inherited immune deficiencies are rare and are often referred to as primary immunodeficiencies. They may affect the production of all immunoglobulins, a single class, or one or more subclasses. Some of these disorders include agammaglobulinemia, common variable immunodeficiency (CVID), x-linked agammaglobulinemia, ataxia telangiectasia, Wiskott-Aldrich syndrome, hyper-IgM syndrome, and severe combined immunodeficiency (SCID).

In CSF, immunoglobulins normally are present in very low concentrations. Increases may be seen, for example, with central nervous system infections (meningitis, encephalitis), inflammatory conditions, and multiple sclerosis.

Decreases in salivary IgA may be seen in those with recurrent respiratory infections.

People with conditions that cause decreased immunoglobulin levels often do not have a strong immune response to vaccinations; they may not produce a sufficient level of antibody to ensure protection and may not be able to receive live vaccines, such as those for polio or measles.

Many laboratory tests measure antibodies in the blood. Those with immunoglobulin deficiencies may have false-negative results on these types of tests. For example, one test for celiac disease detects the IgA class of anti-tissue transglutaminase antibody (anti-tTG). If a person has a deficiency in IgA, then results of this test may be negative when the person, in fact, has celiac disease. If this is suspected to be the case, then a quantitative test for IgA may be performed.

If IgG or IgA concentrations are decreased, or a deficiency in one of their subclasses is suspected, then subclass testing may be performed to detect and further define the deficiency. Subclass deficiencies can be present even when an immunoglobulin class concentration, such as IgG, is normal.

Some people with IgA deficiencies may develop anti-IgA antibodies. When those with anti-IgA are given blood component transfusions that contain IgA (such as plasma or immunoglobulin treatments), they may experience a severe anaphylactic transfusion reaction.

Sometimes an IgM test is used to determine whether a newborn acquired an infection before birth (congenital). IgM may be produced by a developing baby (fetus) in response to infection. Due to the size of IgM antibodies, they cannot pass through the placenta from mother to baby during pregnancy. Thus, any IgM antibodies present in a newborn’s blood are not from the mother but were produced by the baby. This indicates that an infection began during pregnancy.

Infants with otherwise normal immune systems may have temporarily decreased IgG levels when production is delayed. Protection from infections is lost as concentrations of the mother’s IgG in the baby’s blood decrease over several months. The level of IgG remains at low concentrations until the baby’s IgM and IgG production ramps up. This creates a period of time during which the baby is at an increased risk for recurrent infections.

However, infants who are breastfed acquire IgA from breast milk. The IgA in breast milk can be protective against infections, particularly in the time between the decrease of mother’s antibodies and the production of the baby’s own antibodies.

In most cases, immunoglobulins do not respond to lifestyle changes. If you are taking a drug that is decreasing one or more of your immunoglobulins, then you and your healthcare practitioner may decide to alter your medications. It is very important, however, NOT to discontinue or change your medication dosage without consulting with your healthcare provider.

Infants gradually lose protection from infections as the levels of IgG they receive through the placenta from their mothers decrease after birth. Greater protection can be provided for babies through breastfeeding since breast milk contains IgA, which protects against infections.

Not specific ones. Unexplained recurrent infections, multiple infections, or opportunistic infections, with or without chronic diarrhea, may indicate a need to check a person’s immune status. A positive family history of an immunodeficiency may also require follow up. A thorough physical examination and a careful medical history can be critical to a diagnosis.

You may have been directed to give a urine sample to check for the presence of protein in your urine and/or to determine the amount and type of protein present in your urine. Your healthcare practitioner may suspect that, based on your medical history, signs and symptoms and/or other test results, you have a condition associated with abnormal or excessive immunoglobulin production. In such cases, a quantitative immunoglobulin test is often performed along with tests such as serum and urine protein electrophoresis to help establish a diagnosis.