A life-threatening anaphylactic shock can occur if IgA-containing blood is administered to a patient with undiagnosed immunoglobulin A (IgA) deficiency (defined as IgA levels < 500 ng/mL), emphasizing the need for a rapid, point-of-care (POC) method for IgA deficiency screening. The gene discussed is CD79A; the disease is selective IgA deficiency disease.