Acute hemolytic transfusion reaction mediated by anti-Jkb antibody in a pediatric patient with β-thalassemia major: a case report illustrating an anamnestic alloimmune response.

Non-ABO alloantibody-mediated acute hemolytic transfusion reactions are infrequent but life-threatening complications of red blood cell transfusion. Anti-Jkb antibodies are difficult to detect in routine pretransfusion screening due to their low titers, weak avidity, and transient persistence. Here, we report a 16-month-old patient with β-thalassemia major who developed AHTR following transfusion of Jkb-positive RBCs. The patient had received two prior transfusions without documented adverse reactions. However, following the third transfusion, the patient developed acute intravascular hemolysis within two hours, manifesting as tea-colored urine, fever (39.2 °C), and marked hyperbilirubinemia (total bilirubin 173.7 μmol/L). Hemoglobin declined from 62 g/L to 28 g/L over three days. Serologic workup revealed a positive direct antiglobulin test (1+), and antibody screening showed weak agglutination. Serologic workup confirmed the presence of anti-Jkb antibody. Further SCL14A1 genetic testing confirmed the absence of Jkb gene expression, and the patient's Kidd phenotype was determined as Jk (a+wb-). Subsequent transfusion of Jkb-negative, antigen-matched RBCs caused no hemolytic manifestations, and follow-up revealed that the patient's hemoglobin remained stable at approximately 90g/L following red blood cell transfusion. This case highlights the diagnostic challenges associated with anti-Jkb alloantibodies and illustrates the clinical features of an anamnestic alloimmune response. These findings underscore the importance of rigorous antibody screening and antigen-matched transfusion in chronically transfused patients with thalassemia.