RESUMO
BACKGROUND: Kpa antigen is a low incidence red blood cell antigen within the Kell system. Anti-Kpa alloantibody may be associated with acute and delayed hemolytic transfusion reactions. CASE STUDY: We report a case of a clinically significant acute extravascular hemolytic transfusion reaction mediated by previously unrecognized (and undetected) anti-Kpa alloantibody. This reaction occurred in a patient who met all criteria for electronic crossmatch, resulting in the transfusion of an incompatible red cell unit. RESULTS: Post-transfusion investigation showed the transfused red cell unit was crossmatch compatible at the immediate spin phase but was 3 + incompatible at the antiglobulin phase. No evidence of intravascular hemolysis was observed upon visual comparison of the pre- and post-transfusion peripheral blood plasma. Further testing showed the presence of anti-Kpa antibody. The clinical course of the patient included acute febrile and systemic reaction. CONCLUSION: Acute extravascular hemolytic transfusion reaction may occur due to undetected anti-Kpa alloantibody. Various strategies for crossmatching are discussed in the context of antibodies to low incidence antigens.
