Evans syndrome in a pediatric liver transplant recipient with an autoantibody with apparent specificity for the KEL4 (Kp^b) antigen

Although most warm red blood cell (RBC) autoantibodies react broadly with panel cells in addition to the patient's own RBCs, occasionally an autoantibody with specificity for a specific blood group antigen is encountered. Rare cases of warm autoantibodies with specificity for the Kp^b antigen of the Kell blood group system have been described. We report a pediatric transplant recipient with anemia, immune-mediated hemolysis, thrombocytopenia, and a warm autoantibody with apparent anti-Kp^b specificity. The patient's autoimmune anemia and thrombocytopenia responded well to discontinuing the immunosuppressant tacrolimus, trans-fusions with Kp(b-) RBCs, and intravenous immunoglobulin therapy, with disappearance of the pathologic antibody. During the autoimmune hemolysis, the patient's RBCs did not react with antisera specific for Kp^b. However, repeat testing of the patient's RBCs with Kp^b--specific antisera 15 months after the resolution of hemolysis showed reactivity, indicating that the RBC autoantibody was associated with a transient disappearance of the Kp^b antigen.