Acute Hemolytic Transfusion Reaction



Acute Hemolytic Transfusion Reaction (AHTR) is a transfusion reaction caused by host antibody destruction of donor RBCs. This occurs classically due to ABO blood type incompatibility, when the host has antibodies against A and/or B antigens on donor RBCs. This host antibody attack of donor RBCs results in a variety of downstream effects, including complement activation, release of anaphylatoxins, and opsonization of the RBCs. Collectively, these effects explain the clinical manifestations of AHTR. Widespread complement activation and hemolysis induce inflammation and fever, and severe cases can present with hemodynamic instability and flank pain.

Key Points

  • Acute Hemolytic Transfusion Reaction (AHTR)
    • Caused by host antibodies against donor RBCs
      • Example of Type II Hypersensitivity Reaction
      • Antibodies (usually IgM) bind to donor RBCs and activate complement by the Classical Complement Pathway
    • ABO blood group incompatibility (mismatched blood type) is the classic cause
      • Causes reaction within minutes (preformed antibodies vs A/B/O)
      • Minor blood antigens such as Rhesus Factor (Rh), Kell, Lewis, Duffy and  Kidd antigens can also cause hemolysis, but slowly (within 1-6 hours) and with milder symptoms
    • Clinical Features
      • Hemolysis
        • May present as hemoglobinuria (intravascular) or jaundice (extravascular)
        • Intravascular lysis may present as diffuse flank / back pain
          • Pain thought to result from toxicity of free hemoglobin
      • Hemodynamic instability (shock)
        • fever, hypotension, tachypnea, tachycardia
        • Secondary to widespread complement activation