Diagnosis of Selective IgA Deficiency Measurement of serum Ig levels Measurement of antibody response to vaccine antigens Diagnosis of selective IgA deficiency is suspected in patients who have recurrent infections (including giardiasis), anaphylactic transfusion reactions, or a family history of common variable immunodeficiency (CVID), IgA deficiency, or autoimmune disorders or who are taking drugs that lead to IgA deficiency.