Warm autoimmune hemolytic anemia with anti‐Jk<superscript>a</superscript> specificity following babesiosis masquerading as a delayed hemolytic transfusion reaction.

Background: Warm autoimmune hemolytic anemia (WAIHA) is characterized by the development of autoantibodies that react with red blood cells (RBCs) optimally at physiologic temperature, classically resulting in a positive direct antiglobulin test (DAT) for IgG and a panreactive eluate. Babesiosis has been described as a potentiator of WAIHA, and all cases have shown classic blood bank findings. Only rare reports have described autoantibodies, both secondary to babesiosis and overall, with specificity for Kidd antigens. Methods: Antibody detection and identification were performed using IgG‐specific column agglutination technology. Jka antigen phenotyping was assessed using monoclonal reagents and genotypic analysis was performed at an immunohematology reference laboratory. DATs were performed via standard tube methods. The elution was performed using the ELUclear glycine acid red cell elution kit. Results: We report a case of WAIHA induced by Babesia microti infection with an autoantibody with Jka specificity, originally believed to be a delayed hemolytic transfusion reaction, given the detection of an RBC antibody in close proximity to numerous RBC transfusions. Determination of autoantibody status with anti‐Jka‐like reactivity was only confirmed after Kidd antigen genotyping predicted expression of the Jka antigen. Discussion: Healthcare providers should be cognizant of the potential for babesiosis‐induced WAIHA, particularly in individuals who continue to hemolyze despite undetectable parasitemia. Furthermore, this case highlights the possibility for warm autoantibodies to demonstrate Kidd antigen specificity. Though Kidd antigen variants are rare, antigen genotyping may be beneficial, particularly in the context of recent RBC transfusions, which typically preclude accurate serological phenotypic assessment. [ABSTRACT FROM AUTHOR]