Pathophysiology
Clinical meaning
An acute hemolytic transfusion reaction (AHTR) is the most serious and potentially fatal transfusion reaction. It occurs when ABO-incompatible blood is transfused, triggering an immediate antigen-antibody response. The recipient's preformed antibodies (anti-A or anti-B) bind to the corresponding antigens on donor red blood cells, activating the complement cascade. This leads to rapid intravascular hemolysis - the destruction of donor RBCs within the bloodstream. The complement activation releases inflammatory mediators that cause widespread vasodilation, hypotension, and activation of the coagulation cascade. Free hemoglobin released from destroyed RBCs circulates in the plasma, is filtered by the kidneys, and deposits in the renal tubules, causing acute kidney injury. Hemoglobinuria (dark red or cola-colored urine) is a hallmark finding. Disseminated intravascular coagulation (DIC) may develop as the coagulation cascade is massively activated. The most common cause of AHTR is clerical error - mislabeled blood samples, incorrect patient identification, or failure to properly verify the blood product at the bedside. This reaction can occur after infusion of as little as 10-15 mL of incompatible blood, which is why the first 15 minutes of any transfusion...