Clinical Presentation - Mild Allergic (Urticarial) Transfusion Reactions

Mild allergic reactions may occur anytime during the transfusion or shortly thereafter. The typical symptoms are local or generalized urticaria, pruritus, erythema (flushing), and wheezing.

Mechanism

IgE-mediated reactions are type I immediate hypersensitivity reactions. IgE has the ability to bind to mast cells and tissue basophils through Fc receptors on their cell membranes. Mast cells (armed with a surface coating of IgE) are triggered when the patient next becomes exposed to the antigen (allergen) recognized by the IgE. This leads to cross-linking of the bound IgE antibody, producing mast cell degranulation with release of preformed and new mediators of the allergic reaction.

Histamine is the most important preformed mediator. It causes vasodilation, increased vascular permeability, increased mucous secretion by nasal and bronchial glands, and smooth muscle contraction. Other granule compounds that mediate the reaction include heparin, enzymes, leukotrienes, cytokines, and activating factors such as the eosinophil and neutrophil chemotactic factors and platelet activating factor.