Selective IgA deficiency !

The most common immune deficiency: the body makes little or no IgA. Most people are well, but some have infections, allergies or celiac disease.

Updated 2026-11-01

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Why it happens

What it is

A primary antibody deficiency defined by very low or absent serum IgA with normal IgG and IgM and normal vaccine responses, in someone over 4 years old. Most people have no symptoms; some have recurrent mucosal infections, allergy, autoimmune disease or celiac disease, and a few have anti-IgA antibodies that cause severe transfusion reactions.

Who gets it

The most common primary immunodeficiency, with a frequency varying between about 1 in 150 and 1 in 1,000 people depending on ethnic origin; most frequent in people of European ancestry and rarer in East Asians. Most affected people are never diagnosed because they have no symptoms. It is found more often among patients with celiac disease and autoimmune disorders.

Causes

Failure of B cells to switch to and differentiate into IgA-secreting plasma cells; the genetic cause is unknown in most people
Familial clustering, with links to the HLA region and to CVID in the same families
Drug-induced (secondary) cases: some anticonvulsants, sulfasalazine and others, often reversible

Risk factors

Relative with IgA deficiency or CVID
European ancestry
Exposure to drugs associated with secondary IgA deficiency

Pathophysiology

IgA is the main antibody on mucosal surfaces of the respiratory and digestive tracts. Without secretory IgA, mucosal defence against bacteria and parasites is weaker, but IgM can partly compensate, which explains why most people are well. Reduced mucosal barrier function and immune dysregulation favour allergy and autoimmunity. Some patients form IgG or IgE antibodies against IgA, which can trigger anaphylaxis when they receive blood products that contain IgA.

Classification

Complete (absolute) IgA deficiency: serum IgA undetectable or below 7 mg/dL
Partial IgA deficiency: IgA low for age but detectable
Asymptomatic versus symptomatic forms

Symptoms and signs

No symptoms in most people (found incidentally)
Recurrent sinusitis, otitis media, bronchitis and pneumonia
Chronic diarrhoea, giardiasis and malabsorption
Allergic diseases: asthma, allergic rhinitis, food allergy, atopic dermatitis
Autoimmune disease: celiac disease, lupus, rheumatoid arthritis, thyroiditis, inflammatory bowel disease

Diagnosis

Clinical: Suspected in people with recurrent mucosal infections, autoimmunity or celiac disease, or found during workup of a transfusion reaction. Confirmed by isolated low IgA in someone over 4 years old, after excluding other causes of hypogammaglobulinaemia.
Tests: Serum IgA, IgG and IgM (IgA very low with normal IgG and IgM); IgG subclasses and vaccine antibody responses; anti-IgA antibodies before elective transfusion; for celiac screening, use IgG-based tests (IgG anti-tissue transglutaminase or deamidated gliadin peptide) because IgA-based tests are falsely negative.
Imaging: Not needed for diagnosis; sinus or chest imaging only for complications such as chronic sinusitis or bronchiectasis.

Differential diagnosis

Common variable immunodeficiency
IgG subclass deficiency
Transient low IgA in young children (normal before about age 4)
Drug-induced IgA deficiency
Secondary antibody loss (protein-losing enteropathy, nephrotic syndrome)

Goal of treatment

There is no treatment to restore IgA. The aim is to treat infections, allergy and autoimmune disease, prevent transfusion reactions and watch for progression to CVID.

Treatment

Conservative: Education and medical alert identification; asymptomatic people need no specific treatment.
Medical: Early antibiotics for bacterial infections; prophylactic antibiotics for frequent infections.
Conservative: When transfusion is needed in those with complete deficiency or anti-IgA antibodies: washed red cells or IgA-deficient blood products.
Acute: Emergency treatment of a transfusion reaction as anaphylaxis (stop the transfusion, epinephrine, airway and fluids).
Medical: Treatment of associated conditions: gluten-free diet for celiac disease, allergy and autoimmune care; immunoglobulin products only for selected patients with associated IgG deficiency.
Follow-up: Monitoring: periodic immunoglobulin levels and infection history to detect evolution to CVID.

Complications

Anaphylactic transfusion reactions
Recurrent sinopulmonary infections and bronchiectasis
Celiac disease and other autoimmune disorders
Giardiasis and chronic diarrhoea
Progression to common variable immunodeficiency
Slightly increased risk of gastrointestinal cancers and lymphoma

Prognosis

Excellent for most people, who live normal lives without symptoms. Some children recover normal IgA levels over time; a minority develop recurrent infections or autoimmunity or progress to CVID.

Prevention

No primary prevention is known
Carrying medical alert information so that safe blood products are chosen

Test yourself

Think of the answer, then tap the question to see it.

Which is the most common primary immunodeficiency?

Selective IgA deficiency.

What life-threatening reaction can occur with blood transfusion?

Anaphylaxis caused by anti-IgA antibodies reacting to IgA in donor blood or plasma.

Why can celiac screening miss the diagnosis in these patients?

IgA-based tests (IgA anti-tissue transglutaminase) are falsely negative; IgG-based tests must be used.

What are the IgG and IgM levels in selective IgA deficiency?

Normal, with normal vaccine responses.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Selective deficiency of IgA (MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine), 2026).

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