IgA accounts for 13 % of the plasma immunoglobulins and serves to protect the skin and mucosa against microorganisms. It is capable of binding toxins, and in combination with lysozyme develops anti-bacterial and antiviral activity. IgA is the predominant immunoglobulin in bodily secretions such as colostrum, saliva and sweat. Secretory IgA provides defense against local infections and is important in binding food antigens in the gut. In serum, IgA exists in monomeric, dimeric and trimeric forms, whereas in bodily secretions it exists exclusively in dimeric form with an additional chain (secretory component).

Increased polyclonal IgA levels may occur in chronic liver diseases, chronic infections, autoimmune disorders (rheumatoid arthritis, systemic lupus erythematosis), sarcoidosis and Wiscott‑Aldrich syndrome. Monoclonal IgA increases in IgA myeloma.

Decreased synthesis of IgA is observed in acquired and congenital immunodeficiency diseases such as Bruton type agammaglobulinemia. Reduced levels of IgA can be caused by protein-losing gastro-enteropathies and loss through skin from burns.

Due to the slow onset of IgA synthesis, the IgA concentration in serum of infants is lower than in adults.

Use of specific antibodies for quantitation of serum proteins has become a valuable diagnostic tool. Light-scattering properties of antigen/antibody aggregates were first observed by Pope and Healey in 1938, and later confirmed by Gitlin and Edelhoch. Ritchie employed turbidimetric measurements to quantitate specific proteins. Quantitation of immunoglobulins can also be done using nephelometric techniques. Polymeric enhancement with polyethylene glycol (PEG) to improve sensitivity and increase the rate of antigen/antibody complex formation has been described by Lizana and Hellsing.