Allergic reactions are the result of transfusion recipient's antibodies reacting with transfused plasma proteins.
Mild allergic reactions occur in about 1-3% of patients receiving blood products containing plasma. Symptoms are usually mild and include urticaria, erythema (skin redness), and itching. Hives can appear anywhere on the body and may vary in size. Symptoms usually occur within minutes after the start of the transfusion. They can often last for hours or even days. Allergic reactions are more common in patients who have received multiple transfusions.
Anaphylactic reactions are rare but serious. These reactions may occur in patients with anti-IgA when plasma containing IgA proteins are transfused. It is also believed that anaphylactic reactions may be caused by other substances in the donor blood (eg, a peanut allergen transfused to a patient with a peanut allergy). Anaphylactic reactions are severe systemic reactions with symptoms such as hypotension, dyspnea, nausea, vomiting, urticaria, and diarrhea. The most life-threatening symptoms include lower airway obstruction, laryngeal edema, cardiac arrhythmia, cardiac arrest, shock, and loss of consciousness.
Fever is not a symptom that is associated with an allergic reaction.