Diagnostic Criteria for Selective IgA Deficiency

Core Diagnostic Requirements

The European Society for Immunodeficiencies requires patients to be older than 4 years of age, with serum IgA level less than 7 mg/dL, normal IgG and IgM levels, normal vaccine responses, and exclusion of secondary causes of hypogammaglobulinemia 1, 2, 3
Approximately two-thirds of patients with IgA <7 mg/dL have detectable but very low levels; one-third have completely absent IgA 1
IgG levels must be normal for age, and IgM levels must be normal for age, to distinguish selective IgA deficiency from more severe combined immunodeficiencies like CVID 1, 2, 3
Other causes of hypogammaglobulinemia, such as medication-induced IgA deficiency and secondary causes like HIV infection, must be excluded 1, 2, 3, 4, 5

Patients with IgA levels between 7 mg/dL and the lower limit of normal should NOT be diagnosed with selective IgA deficiency 1, 2, 3
Most clinical laboratories cannot accurately measure IgA levels below 7 mg/dL, and only specialized laboratories can determine whether IgA is truly absent or present at detectable but very low levels 1
Medication history is essential, as drug-induced IgA deficiency may be reversible upon cessation of the offending agent 1, 5

Patients must be monitored over time for development of complications, including respiratory and gastrointestinal infections, atopy, autoimmune diseases, celiac disease, and malignancy 1, 2, 3
Some patients with SIGAD will evolve to CVID later in life, necessitating ongoing immunologic surveillance 1, 4, 5
Familial clustering is observed, with 20-25% of patients having a family history of either SIGAD or CVID, suggesting a shared genetic susceptibility 1, 5

Prevalence varies dramatically by ethnicity, with 1 in 300-700 among white populations versus approximately 1 in 18,000 in Asian populations 1, 5
Male predominance may exist, though data are limited 1, 5

Low secretory IgA indicates a deficiency in the primary antibody that protects mucosal surfaces, most commonly representing selective IgA deficiency (SIGAD), which predisposes patients to recurrent sinopulmonary and gastrointestinal infections, autoimmune disorders, and allergic diseases 6
Recurrent sinopulmonary infections (sinusitis, bronchitis, pneumonia) and gastrointestinal infections are the hallmark manifestations, though many patients remain asymptomatic 6, 7

Measure total IgG, IgM, and IgG subclasses (IgG1-4) to identify combined deficiencies 6, 8
Measure specific antibody responses to pneumococcal polysaccharide vaccine (23-valent) before and 4 weeks after immunization to assess functional antibody production 6, 9
Test responses to protein antigens (tetanus, diphtheria) to evaluate overall humoral immunity 7, 10

IgA deficiency combined with IgG subclass deficiency (especially IgG2) or defective specific antibody production requires aggressive management 6
Poor response to pneumococcal polysaccharide vaccine (concentration >1.3 mg/mL for <70% of serotypes in patients >6 years) indicates high-risk features 6, 9
Implement prophylactic antibiotics for patients with recurrent sinopulmonary infections that negatively impact quality of life 8
IVIG therapy should be considered when recurrent infections persist despite aggressive antibiotic therapy, significantly affect quality of life, or evidence of permanent organ damage (bronchiectasis) is present 8

Do not administer blood products containing IgA to patients with undetectable IgA, as they may develop anti-IgA antibodies and risk anaphylaxis 6
IgG4 deficiency should not be diagnosed in children under 10 years, as levels are normally very low 8