Table 1.

European Society for Immunodeficiencies’' differential diagnosis for IgA deficiency in individuals with recurrent bacterial infections, autoimmune disease and/or family history. Adapted from ESID Working Definitions for Clinical Diagnosis of PID [4].

Primary Immunodeficiency	Diagnostic Criteria
Selective IgA deficiency	Undetectable serum IgA, or less than 7 ​mg/dl when detected by nephelometry, in patients greater than 4 years old with normal levels of immunoglobulin G and M, normal vaccine response, and with the exclusion of secondary causes of hypogammaglobulinemia and T-cell defects
IgA with IgG subclass deficiency	Undetecable serum IgA or less than 7 ​mg/dl when detected by nephelometry, in patients greater than 4 years old with normal/lowish levels of immunoglobulin G and M, normal vaccine response to some vaccinations, and with the exclusion of secondary causes of hypogammaglobulinemia and T-cell defects AND low levels in one or more IgG subclass
Specific antibody deficiency (SPAD)	Normal serum immunoglobulin G, A, M, and IgG subclasses, with a severely altered polysaccharide vaccine response after documented invasive infection or immunization, and with the exclusion of T-cell defects
Common variable immunodeficiency disorders (CVID)	Decreased serum IgG of less than 2 standard deviations for age, in patients greater than 4 years old with marked decrease in IgA with or without low IgM, with the exclusion of secondary causes of hypogammaglobulinemia and severe T-cell deficiency AND severely altered vaccine response after natural infection or immunization OR memory B cells less than 70% of age-appropriate normal
Unclassified antibody deficiency	Decreased level of at least one of the following: immunoglobulin G, A, M or IgG subclass or severely altered vaccine response, and with the exclusion of secondary causes of hypogammaglobulinemia and T-cell defects AND does not meet classification under any other working definition of an antibody deficiency