ABSTRACT
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 Kpb 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-Kpb 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 Kpb. However, repeat testing of the patient's RBCs with Kpb-specific antisera 15 months after the resolution of hemolysis showed reactivity, indicating that the RBC autoantibody was associated with a transient disappearance of the Kpb antigen.
