Immune hemolysis may occur when red cells are transfused into a patient with a pre-existing antibody that destroys the transfused incompatible red cells. This may be either immediate or delayed destruction of the donor red cells. Acute intravascular hemolysis most commonly occurs from the transfusion of ABO-incompatible blood. Naturally occurring ABO antibodies bind complement on the red cell surface and have efficient lytic properties, which cause intravascular hemolysis. Extravascular hemolysis is characterized by antigen-antibody complexes, which do not activate complement.
Acute intravascular hemolysis is characterized by the rapid destruction of red cells immediately after transfusion. Rapid hemolysis of as little as 10 mL of incompatible red cells can produce symptoms of an acute hemolytic transfusion reaction (AHTR). Signs and symptoms can occur within minutes after starting the transfusion.
Clerical errors, such as mislabeled patient samples and mislabeled blood products, could result in AHTR. Therefore, a system must be in place and rigidly followed to ensure samples and blood products are correctly identified.
Although acute hemolytic reactions are rare, they are the most dangerous and are often life-threatening.
