Pathophysiology
Clinical meaning
Anaphylactic transfusion reactions are rare but life-threatening type I hypersensitivity responses that occur within seconds to minutes of starting a transfusion. The most well-characterized mechanism involves patients with selective IgA deficiency who have developed anti-IgA antibodies from prior transfusion or pregnancy exposure. When these patients receive blood products containing IgA (present in plasma), the anti-IgA antibodies trigger massive mast cell and basophil degranulation. This degranulation releases histamine, leukotrienes, and prostaglandins, causing severe bronchospasm, laryngeal edema, profound vasodilation, and increased vascular permeability. The result is a rapid-onset anaphylactic response with airway compromise and circulatory collapse. Unlike allergic (urticarial) reactions which are localized and mild, anaphylactic reactions are systemic and can be fatal without immediate intervention. Selective IgA deficiency is the most common primary immunodeficiency, affecting approximately 1 in 300 to 1 in 700 individuals. However, only a small percentage of IgA-deficient patients develop clinically significant anti-IgA antibodies. For patients with known IgA deficiency, blood products must be obtained from IgA-deficient donors or the plasma must be washed to remove IgA-containing plasma.