This page is all about medical alert cards and how they can help prevent a serious and sometimes fatal side effect of alloimmunization: hemolytic transfusion reactions (HTRs). If a patient with alloantibodies receives blood that is not matched to his/her antibody status, the transfused blood cells are destroyed by the patient’s immune system. HTRs can result in a variety of problems, including: a systemic inflammatory response, low blood pressure, kidney failure, and even death. Alloantibodies are the second leading cause of fatal HTRs. A review of current literature shows that hemolytic transfusion reactions are still a problem for alloimmunized patients today and that the risks can be prevented by a medical alert card. Patients can create their own custom cards here.