Anaphylaxis

Potentially life-threatening type I hypersensitivity reaction involving mast cell degranulation and manifested by urticaria, angioedema, respiratory distress, and gastrointestinal symptoms. In the context of transfusion medicine, anaphylactic (anaphylactoid) reactions occur when donor plasma in a blood component is transfused to a recipient with preformed antibodies. This is often seen in recipients who are IgA deficient.