Acute Immune Hemolytic Transfusion Reactions

Description

Acute Hemolytic Transfusion Reactions (AHTR) of immune origin are serious, potentially life-threatening reactions, usually caused by transfusion of ABO-incompatible red cells (and rarely ABO-incompatible plasma) following clerical or systems errors that result in incompatibility of the blood unit with the blood recipient. The most common cause of this is misidentification of the blood recipient, which may occur at any of the following steps:

• drawing the recipient's crossmatch specimen
• labelling the recipient's blood specimen
• performing pretransfusion testing in the transfusion service
• issuing the donor blood from the transfusion service
• identifying patient and donor unit immediately prior to transfusion

Incidence

The incidence of AHTR varies with location and when data were gathered. A recent estimate of the risk of AHTR in Canada is approximately 1:12,500 units of red cells with over 90% occurring as a result of ABO errors (See Kleiman S in Further Reading).The typical AHTR ensues when patient anti-A or anti-B react with A and/or B antigens on the transfused donor red cells triggering the binding of complement with subsequent activation of the complement cascade resulting in Intravascular Hemolysis (IVH).

Preventing hemolytic transfusion reactions depends on proper patient identification and labelling of samples and blood components in each and every step, from sample collection to blood administration.NOTE: Less frequently, so-called minor ABO incompatibilities (donor ABO antibodies reacting with A and/or B antigens on the patient's red cells), may cause acute hemolysis. Reactions due to donor antibodies are usually considered low risk for hemolytic reactions due to the small volume of donor plasma in most blood components (except for plasma and apheresis platelets), which would be diluted by the patient's blood volume; as well, soluble A and B antigens in patient plasma help to neutralize the donor antibodies.However, severe life-threatening hemolytic transfusion reactions and death have been reported when a donor has a very high titre of anti-A or anti-B. These reactions are often associated with Single-Donor apheresis platelets (SDPs), which may contain 200 to 400 mL of plasma (see Larsson et al. in Further Reading).

An atypical form of Acute Hemolytic Transfusion Reaction has been reported in patients with Sickle Cell Disease (SCD) following transfusion of compatible RBC that may or may not have an immune mechanism. The pathophysiology is not well-understood; hypotheses include a bystander hemolysis mechanism, suppression of erythropoiesis, or hyperactive macrophages (see Further Reading).