What is the expected outcome if a patient has a history of anti-Jk^a antibodies and receives Jk^a positive blood?

When a patient with a history of anti-Jk^a antibodies receives Jk^a positive blood, a severe hemolytic transfusion reaction is expected. This occurs because the patient's immune system has already been sensitized to the Jk^a antigen, and the presence of circulating anti-Jk^a antibodies will target the Jk^a positive red blood cells for destruction.

In this situation, upon introduction of the incompatible Jk^a positive blood, the antibodies bind to the antigens on the transfused red blood cells. This can trigger complement activation and lead to a rapid and potentially life-threatening hemolysis of the transfused cells. The severe reaction can manifest with symptoms such as fever, chills, back pain, and hemoglobinuria, and requires immediate medical intervention.

Overall, the presence of pre-existing antibodies like anti-Jk^a in the patient poses a significant risk for severe hemolytic reactions upon transfusion of incompatible blood types. This understanding emphasizes the importance of thorough blood type and antibody screening prior to transfusions to prevent adverse outcomes.