Transfusion reactions are classified by mechanism into five categories summarized by the mnemonic FHALO: febrile non-hemolytic (cytokine-mediated), hemolytic (acute intravascular, a type II hypersensitivity reaction from ABO incompatibility; and delayed extravascular, from prior sensitization to non-ABO antigens), allergic (type I hypersensitivity to donor plasma proteins, ranging to anaphylaxis, notably in IgA-deficient patients who form anti-IgA antibodies), TRALI (transfusion-related acute lung injury, an inflammatory non-cardiogenic pulmonary edema from donor antibodies activating pulmonary neutrophils), and TACO (transfusion-associated circulatory overload, a cardiogenic pulmonary edema from volume overload). Each reaction has a distinct pathophysiologic mechanism, timing, and clinical/laboratory signature that differentiates it from the others, forming the diagnostic and management framework within transfusion medicine/immunohematology.
Transfusion reactions are classified by mechanism into five categories summarized by the mnemonic FHALO: febrile non-hemolytic (cytokine-mediated), hemolytic (acute intravascular, a type II hypersens…