Why can IgA-deficient patients have a severe allergic reaction to donated blood?

Patients who are IgA-deficient do not naturally produce immunoglobulin A (IgA). When these individuals receive a blood transfusion, their immune systems may recognize the IgA present in the donor's plasma as a foreign substance. Consequently, these patients develop antibodies against the donor IgA, which can trigger a severe allergic reaction known as anaphylaxis.1

This reaction is life-threatening and is characterized by a severe drop in blood pressure, vascular collapse, and respiratory distress. To prevent this, medical professionals may use blood components sourced from IgA-negative donors or utilize washed red cells to effectively remove the remaining plasma that contains IgA.1