Allergic reactions to transfusion are common (1-3% of all transfusions); however, most allergic reactions are mild and are limited to urticaria, pruritis, and flushing. More severe anaphylactic reactions present with respiratory symptoms similar to those of TRALI and TACO. Symptoms include bronchospasm, angioedema, and hypotension. The incidence of anaphylactic reactions range from 1:18,000 to 1:172,000 transfusions depending upon the populations studied and method of reporting. ATRs are more common in plasma transfusions with an incidence ranging from 1:591-1:2184 FFP units transfused. The etiology of allergic reactions is not entirely clear, although some allergies to specific plasma proteins have been identified, including IgA and haptoglobin.