Test Center

My Recent Searches

  • No Recent Search.

My Tests Viewed

  • No Test Viewed.

IgA Subclasses

IgA Subclasses

Test Highlight

IgA Subclasses


Clinical Use

  • Diagnose IgA subclass deficiencies

  • Determine etiology of recurrent infections

  • Diagnose infection

  • Diagnose inflammation

  • Diagnose IgA monoclonal gammopathy

Clinical Background

IgA is the first line of defense for the majority of infections and consists of 2 subclasses. IgA1 is the dominant subclass, accounting for 80% to 90% of total serum IgA and greater than half of the IgA in secretions such as milk, saliva, and tears. IgA2 is more concentrated in secretions than in blood. IgA2 is more resistant to proteolytic cleavage and may be more functionally active than IgA1.

A deficiency in an IgA subclass may result in a compensatory increase in the other IgA subclass. Also, IgA deficiencies are often associated with a deficiency in one or more IgG subclasses, leading to an additive effect in causing recurrent infections. The majority of published studies address total IgA deficiency, not selective deficiency of either subclass. Diseases associated with IgA deficiency include ataxia telangiectasia, common variable immunodeficiency, and recurrent respiratory tract infections. Immunoglobulin replacement therapy may be of benefit.

Elevated levels of an IgA subclass may reflect infection, inflammation, or IgA monoclonal gammopathy.


Three antibodies—1 anti-IgA, 1 monospecific for IgA1, and 1 monospecific for IgA2—are utilized. These antibodies bind to the IgA, IgA1, and IgA2 antigens, respectively, forming insoluble immune complexes that scatter light. The light-scatter is directly related to the antigen concentration and is determined in a nephelometer. Results are reported as mg/dL.

Interpretive Information

Very high levels of either IgA subclass are associated with IgA myeloma. IgA2 deficiencies may be associated with recurrent sinopulmonary infections.


Content reviewed 04/2013

top of page

* The tests listed by specialist are a select group of tests offered. For a complete list of Quest Diagnostics tests, please refer to our Directory of Services.