Allergic, anaphylactoid and anaphylactic reactions
This chapter discusses allergic, anaphylactoid and anaphylactic reactions following blood transfusion. Allergic reactions can occur following blood transfusion, and are the result of an interaction between an allergen and preformed antibody, usually IgF. The severity of the allergic reactions range from focal mild urticarial reactions to systemic, life-threatening anaphylactic reactions with intractable hypotension or shock and loss of consciousness. Anaphylactoid is used to describe reactions less severe than anaphylaxis that are characterized by hypotension, dyspnea, stridor, wheezing and diarrhea. Allergic reactions are usually type 1 hypersensitivity responses, mediated by IgE. Individuals with congenital complete IgA deficiency may develop a class-specific antibody to IgA (anti-IgA) and exposure to IgA will generate an immediate anaphylactic reaction. Patients with severe allergic, anaphylactoid or anaphylactic reactions should have their pretransfusion sample tested for the presence of IgA by nephelometry which is a simple and rapid test. Anaphylactic reactions have been reported in individuals who lack allotypes of other normal serum proteins such as haptoglobin, who form IgG or IgE antibodies against these proteins.