Immunoglobulins (IgG,IgA,IgM)

A test for quantitative 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.

Immunoglobulins, also called antibodies, are proteins produced by plasma cells. They target specific "threats" and play a key role in the body's immune system. Immunoglobulins are produced in response to exposure to bacteria, viruses, and other microorganisms as well as other substances that are recognized by the body as "non-self" harmful antigens.

In general, immunoglobulin disorders can be classified as:

• Immunoglobulin excess
  • Polyclonal: Excess is the sum of immunoglobulins from many different immune (plasma) cells
  • Monoclonal: Excess immunoglobulins are from the clones of one plasma cell

• Immunoglobulin deficiency
  • Secondary (acquired)—the most common are caused by an underlying condition or contributing factor
  • Primary (inherited)—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.