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Allergic Reactions

Simple allergic reactions are the second most common type of transfusion complication. Allergic reactions occur most commonly after the transfusion of components containing large volumes of plasma such as fresh frozen plasma, plasma frozen within 24 hours, single donor platelets or pooled random donor platelet concentrates. Transfusion of red blood cells is less commonly associated with allergic reactions because they contain so little plasma.

Etiology: Allergic reactions are attributed to soluble substances in donor plasma (e.g. food allergens, drugs or ethylene oxide) which react with IgE antibody bound to basophils or mast cells in the recipient's blood. This interaction results in the release of C3a, C5a, histamine, prostaglandin D2, leukotrienes C and D4 and a variety of other cytokines. These substances produce an immediate type hypersensitivity reaction by increasing vascular permeability, promoting bronchial smooth muscle contractions, and stimulating mucus secretion by nasal and bronchial glands. Histamine release causes hives, itching, and rarely, laryngeal edema.

Symptoms: Hives (urticaria) or other rash (erythema), itching (pruritis), and wheezing are most common. Allergic reactions can occur during or up to 3 hours post-transfusion. The shorter the time interval is between the start of the transfusion and the onset of the allergic reaction, the more severe the reaction. In more severe reactions, anxiety, dyspnea, palpitations, fever and chills may accompany urticaria.

Consequences: Allergic reactions are not usually dangerous, but they do cause discomfort and anxiety. Urticaria is not a manifestation of a hemolytic reaction, so it is not usually necessary to discontinue the transfusion. Lab Data: No laboratory testing is necessary.


  • Slow the rate of transfusion for 15 to 30 minutes.
  • Give an antihistamine to ease discomfort.
  • Monitor carefully because urticaria could be the first sign of a more serious allergic reaction.
  • If the only symptom is skin rash or hives and the symptoms resolve within 30 minutes of treatment, the transfusion can be resumed.

Prevention: Patients who have had 2 or more allergic reactions benefit from oral or parenteral prophylactic treatment with diphenhydramine one hour prior to transfusion and at the start of transfusion. If reactions continue, cellular products can be washed to remove residual plasma containing the soluble allergens. Corticosteroids may be necessary in severe, repetitive cases.. 

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