Anaphylactic transfusion reactions occur after infusion of as little as a few milliliters of blood or plasma. Anaphylaxis is characterized by coughing, bronchospasm, respiratory distress, vascular instability, nausea, abdominal cramps, vomiting, diarrhea, shock, and loss of consciousness. Some reactions occur in patients with IgA deficiency who have developed anti-IgA antibodies after immunization through previous transfusion or pregnancy. This reaction is life-threatening.