Table 1. IUIS phenotypical classification–predominantly antibody deficiencies (without an identified monogenetic origin).

Phenotypical classification	Criteria
Hypogammaglobulinemia
Common variable immunodeficiency (CVID) Phenotype (with no known disease-causing monogenic defect specified)	Decrease of IgG, IgA and/or IgM AND secondary causes of hypogammaglobulinemia have been excluded AND B cells > 1% Clinical phenotypes vary: most have recurrent infections, some have polyclonal lymphoproliferation, autoimmune cytopenias and/or granulomatous disease
Other antibody deficiencies	Isotype, light chain or functional deficiencies with generally normal numbers of B cells
IgG subclass deficiency with IgA deficiency	Recurrent bacterial infections May be asymptomatic Reduced IgA with decrease in one or more IgG subclass(es)
Isolated IgG subclass deficiency	Usually asymptomatic A minority may have poor antibody response to specific antigens and recurrent viral/bacterial infections Reduction in one or more IgG subclass(es)
Selective IgM deficiency	Pneumococcal/ bacterial infections Absent serum IgM
Selective IgA deficiency	May be asymptomatic Bacterial infections, autoimmunity mildly increased Very low to absent IgA with other isotypes normal, normal subclasses and specific antibodies
Specific antibody deficiency with normal immunoglobulin levels and normal B cells	Reduced ability to produce antibodies to specific antigens Immunoglobulin levels normal

Source: Bousfiha et al. [3].