K antigen

The K-antigen belongs to the Kell antigen system. It is present on the red cells of 9% of white, 2% of black and rare in East Asian patients. The K-antigen is strongly immunogenic. Anti-K antibodies are usually formed in response to transfusion or pregnancy and can cause both hemolytic transfusion reactions and hemolytic disease of the fetus and newborn (HDFN).