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Selective IgA deficiency

Selective IgA deficiency is a primary immunodeficiency characterized by an undetectable level of immunoglobulin A (IgA) in the blood and secretions but no other immunoglobulin deficiencies.


Individuals with selective IgA deficiency (SIgAD) lack immunoglobulin A (IgA), but they usually have normal amounts of IgG and IgM. SIgAD is relatively common in people of European descent and rare in people of Asian descent. In North America, it is the most common form of primary immunodeficiency (PI), estimated to affect 1 in 500 people. Many affected individuals have no symptoms and do not even know they have a deficiency until the lack of IgA is noted when they are being evaluated for another condition, such as celiac disease. Those people who are symptomatic may develop a variety of significant clinical problems, including infections, allergies, and autoimmune diseases. It is important to know that, with the exception of an undetectable level of IgA, all other components of the immune system are usually functional. 

SIgAD is defined as a primary immunodeficiency characterized by an undetectable level of IgA in the blood and secretions but normal IgG and IgM in an individual age 4 and older. IgM and IgG mainly protect people from infections inside body tissues, organs, and blood. While IgA is present in the blood, most of the IgA in the body is in the secretions of the mucosal surfaces, including tears, saliva, and colostrum, as well as genital, respiratory, and gastrointestinal secretions. The IgA antibodies in these secretions play a role in protecting people from infections in the respiratory tract, gastrointestinal tract, and genitourinary tract. 

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Individuals with SIgAD lack serum (IgA <7 mg/dl) and secretory IgA, but they do make all the other immunoglobulin classes. Some of the individuals with SIgAD also have IgG subclass deficiency. Among the four IgG subclasses, low IgG2 levels are most commonly observed. In those who have associated allergic diseases, serum IgE levels may be increased. In those with SIgAD who have an autoimmune disease, a variety of autoantibodies (like ANA or rheumatoid factor) may be positive. In most people with SIgAD, there are no problems with cellular immunity, the complement system, or white blood cell function.

Secretory IgA has some differences compared to the IgA present in the blood. Secretory IgA is made of two IgA antibody molecules joined together by a protein called the J chain—J for joining. In order for this unit to be secreted, it is attached to another protein called the secretory piece. Therefore, the final secretory IgA unit that protects the mucosal surfaces is actually composed of two IgA molecules joined by the J chain and attached to the secretory piece. The secretory IgA is able to exist in the gastrointestinal tract because it is resistant to gastrointestinal enzymes.

IgA promotes health by regulating the composition and function of microbiota, which regulates metabolism, epithelial barrier integrity, and the immune system. 

Clinical presentation

A common problem in SIgAD is susceptibility to infections. Problems with infections are seen in about half of the individuals with SIgAD. Recurrent ear infections, sinusitis, bronchitis, and pneumonia are the most common infections. Some individuals may develop gastrointestinal infections and other gastrointestinal disorders, such as chronic diarrhea. 

Another problem with SIgAD is the occurrence of autoimmune diseases. These are found in about one-third of individuals who seek medical help. Some of the more frequent autoimmune diseases associated with SIgAD include rheumatoid arthritis, celiac disease, systemic lupus erythematosus, and idiopathic thrombocytopenic purpura (ITP) (low platelet counts). Other kinds of autoimmune diseases may affect the endocrine system and/or the gastrointestinal system. 

Allergic disorders are more common among individuals with SIgAD than among the general population. The types of allergies associated with SIgAD include allergic rhinitis, allergic conjunctivitis, eczema, and asthma. Food allergy may also be associated with SIgAD. 


The diagnosis of SIgAD is usually suspected because of chronic or recurrent ear infections, sinusitis, respiratory tract infections, chronic diarrhea, or some combination of these problems. Other individuals are identified when immunoglobulin testing is ordered for some non-immunologic problem, for example when a person is being evaluated for possible celiac disease. The diagnosis is established when blood tests demonstrate undetectable levels of IgA (reported usually as <7 mg/dL), with normal levels of the other major classes of immunoglobulins (IgG and IgM). The healthcare provider may order several other tests including autoantibodies.

Prevalence and inheritance

Genetic susceptibility in IgA deficiency is not well defined, but familial inheritance of SIgAD may occur in approximately 20% of cases. SIgAD is also observed in families with common variable immune deficiency (CVID). There are reports of some individuals with SIgAD being later diagnosed with CVID. 


An ideal treatment for SIgAD would be to replace IgA. However, no IgA-enriched immunoglobulin (Ig) preparation is available in the U.S. Treatment should be directed toward a specific illness. For example, individuals with chronic or recurrent infections need treatment with appropriate antibiotics. Ideally, antibiotic therapy should be targeted at the specific organism causing the infection. It is not always possible, however, to identify these organisms and their antibiotic sensitivities precisely, and therefore, the use of broad-spectrum antibiotics may be indicated. Certain individuals who have chronic sinusitis or chronic bronchitis may need to stay on long-term preventive antibiotic therapy (antibiotic prophylaxis). In these cases, the healthcare provider and person with SIgAD need to discuss the benefits and risks of the various possibilities and reach a mutual agreement regarding treatment.

People with SIgAD (<7 mg/dL) are often considered to be at increased risk of life-threatening allergic reactions, also known as an anaphylactic reaction, to blood and blood products, including immunoglobulin (Ig) replacement therapy that may contain traces of IgA. This is thought to be due to antibodies (IgE) against the IgA antibody, which may be found in some IgA-deficient individuals. These reactions, however, are very rare overall. 

If individuals with SIgAD and IgG2 subclass deficiency have a history of recurrent serious infections, a trial of Ig replacement therapy may be used to prevent infections. If there is a concern about the risk of adverse reactions because of the small amounts of IgA in intravenous immunoglobulin (IVIG) preparations, then it is advised to use subcutaneous immunoglobulin (SCIG). The latter is preferred over low IgA-containing preparations administered intravenously because of the following reasons: there is only one IVIG preparation with extremely low IgA, infusions need to be given in a hospital setting and under medical supervision, and anaphylactic reaction to SCIG has not been reported. Individuals with SIgAD who need a blood transfusion should receive washed red cells to remove the plasma that contains the IgA that may cause a transfusion reaction.

As for autoimmune diseases, a variety of therapeutic options exist, such as anti-inflammatory drugs, steroids, or biological drugs. As with every treatment, the individual and/or caregiver and their healthcare provider should discuss the treatment plan and best treatment options. 


Although SIgAD is usually one of the milder forms of immunodeficiency, it may result in severe disease in a subset of people. Therefore, it is difficult to predict the long-term outcome in an individual with SIgAD, although generally, the prognosis is considered to be very good. It is important for healthcare providers to continually assess and re-evaluate individuals with SIgAD for the existence of associated diseases and to consider the possibility of later diagnosis with a more extensive immunodeficiency like CVID.

Individuals need to inform their healthcare providers of anything unusual, especially fever, productive cough, skin rash, or sore joints. The importance of good communication with the healthcare provider and initiating appropriate therapy as soon as necessary cannot be overstated.

This page contains general medical and/or legal information that cannot be applied safely to any individual case. Medical and/or legal knowledge and practice can change rapidly. Therefore, this page should not be used as a substitute for professional medical and/or legal advice.

Adapted from the IDF Patient & Family Handbook for Primary Immunodeficiency Diseases, Sixth Edition 
Copyright ©2019 by Immune Deficiency Foundation, USA