Long‐read DNA sequencing resolves a rare case of alloimmune hemolysis mimicking autoimmune hemolysis

Background Immune hemolytic anemia poses a significant challenge in transfusion medicine, as identification of underlying alloantibodies can be masked by warm and/or cold autoantibodies. This increases the risk of transfusing incompatible blood, which can precipitate or exacerbate hemolysis. Identifying alloantibodies in the presence of autoantibodies remains difficult with standard serologic and genotypic methods, often delaying accurate diagnosis and appropriate transfusion strategies. Case Report We describe a 63‐year‐old woman with autoimmune hemolytic anemia who suffered near‐fatal hemolysis following transfusion. Despite extensive serologic and genotypic testing, the cause of her hemolytic transfusion reactions remained elusive. Given her clinical course and transfusion history, we hypothesized that her acute hemolytic transfusion reactions could be due to immune sensitization to a high‐incidence RBC antigen. Research whole‐genome long‐read sequencing (LRS) revealed homozygosity for a rare KEL*02N.16 allele, consistent with a rare Ko phenotype, which was validated by Sanger sequencing. Retrospective serologic testing with Ko RBCs further confirmed alloimmunization within the Kell system. Conclusion This case highlights the limitations of conventional serologic and genotypic methods in detecting rare blood group phenotypes, and emphasizes the diagnostic power of long‐read sequencing in transfusion medicine. Early molecular testing in complex hemolytic cases can facilitate targeted transfusion strategies, reduce the risk of severe hemolysis, and improve patient outcomes. As sequencing technologies become more accessible, they have the potential to revolutionize blood group typing and alloimmunization risk assessment in clinical practice.