IgG, IgA, IgM

CLINICAL UTILITY:

The fluctuation of serum levels of the immunoglobulins (antibodies) G, A and M, often reflects a response to infections, since their primary function is protection against various foreign agents. Patterns of increase or decrease can be significant in the diagnosis of the monoclonal gammopathies in which only one restricted variant of immunoglobulin is present in large amounts. Polyclonal increases occur in chronic and acute infections and inflammations, conditions associated with a number of parasite, bacterial and viral diseases, autoimmune disorders, and liver diseases. Increases in IgG generally predominate in chronic conditions such as chronic active hepatitis and autoimmune diseases. Since IgM appears in the primary immune response, increases are generally associated with viral infections and biliary cirrhosis. IgA increases often are found with respiratory and gastrointestinal infections and malabsorption or malnutrition.

Each of these immunoglobulins may comprise monoclonal spikes. Decreases usually suggest a disorder in immunoglobulin metabolism or formation, whether of primary or secondary origin. Primary conditions include the genetic immunodeficiencies. The secondary deficiencies usually accompany other diseases, or occur as the result of immunosuppressive therapy.

METHOD DESCRIPTION:

Single radial immunodiffusion (RID) is the method used to quantify the immunoglobulins G, A, and M. If a monoclonal component is present, the RID value is not valid, since different anti-immunoglobulin antisera may react aberrantly with monoclonal immunoglobulins. Therefore, abnormally elevated levels of immunoglobulins are checked with agarose electrophoresis, and with immunofixation, if necessary. Monoclonal immunoglobulins will be quantified by electrophoresis, rather than RID, since protein electrophoresis is the method of choice to follow the levels of a monoclonal spike.

REFERENCE RANGE:

IgG: 650-1600 mg/dl
IgA: 90-425 mg/dl
IgM: 50-300 mg/dl

SPECIMEN REQUIREMENTS:

0.3 ml serum, for individual immunoglobulins, or 1.0 ml serum for IgG, IgA, and IgM ordered together. Freeze.