Anti-Fy^a-mediated delayed hemolytic transfusion reaction following emergency-release red blood cell transfusion: possible involvement of HLA-DRB1*04:03 in the Japanese population

A 43-year-old Japanese male, who had undergone open liver surgery for tumor resection, presented with decreased hemoglobin levels on Day 13 post-emergency-release transfusion of 16 units of Fy(a +) red blood cells. As the anemia was accompanied by increased lactate dehydrogenase, indirect bilirubin, and reticulocytes, as well as decreased haptoglobin, it was attributed to hemolysis. In the diagnostic workup for hemolytic reaction, the direct antiglobulin test result for IgG was positive and the antibody dissociated from the patient’s peripheral red blood cells was identified as anti-Fy^a (titer, 4). The hemolytic reaction was transient (approximately 10 days), of moderate severity, and did not result in any obvious organ damage. However, a single compatible red blood cell transfusion of 2 units was required on Day 17 after the causative transfusion. Notably, HLA typing revealed that the patient carried the HLA-DRB1*04:03 allele, which has been implicated in immunogenicity and induction of anti-Fy^a response in Caucasian populations. In summary, this is the first documented case of definitive anti-Fy^a-mediated delayed hemolytic transfusion reaction associated with HLA-DRB1*04:03 in the Japanese population.