| TYPE | PATHOGENESIS | CLINICAL PRESENTATION | TIMING |
| Allergic/anaphylactic reaction | Type I hypersensitivity reaction against plasma proteins in transfused blood. IgA-deficient individuals must receive blood products without IgA. | Urticaria, pruritus, fever, wheezing, hypotension, respiratory arrest, shock. | Within minutes to 2–3 hours |
| Febrile nonhemolytic transfusion reaction | Two known mechanisms: type II hypersensitivity reaction with host antibodies against donor HLA and WBCs; and induced by cytokines that are created and accumulate during the storage of blood products. | Fever, headaches, chills, flushing. | Within 1–6 hours |
| Acute hemolytic transfusion reaction | Type II hypersensitivity reaction.
Intravascular hemolysis (ABO blood group incompatibility) or extravascular hemolysis (host antibody reaction against foreign antigen on donor RBCs). |
Fever, hypotension, tachypnea, tachycardia, flank pain, hemoglobinuria (intravascular hemolysis), jaundice (extravascular). | Within 1 hour |
| Transfusion-related acute lung injury | Donor anti-leukocyte antibodies against recipient neutrophils and pulmonary endothelial cells. | Respiratory distress and noncardiogenic pulmonary edema. | Within 6 hours |