A rare case of naturally occurring anti-Jka antibody detected in a 6-month-old infant.

INTRODUCTION: Antibodies of the Kidd blood group system are associated with hemolytic transfusion reactions and, less commonly, hemolytic disease of the fetus and newborn. Naturally occurring antibodies against Kidd antigens are exceedingly rare, with a limited number of cases reported worldwide. We report a case of a naturally occurring anti-Jka antibody detected in a 6-month-old male infant. METHODS: The patient was admitted with a high fever after routine age-appropriate vaccinations. He had no history of blood transfusion, underlying disease, or perinatal complications. Blood, urine, and cerebrospinal fluid cultures were negative, while respiratory viral polymerase chain reaction was positive for human coronavirus 229E. RESULTS: As part of the routine admission protocol, blood grouping and antibody screening were performed, and subsequent antibody identification confirmed the presence of anti-Jka. Serologic testing showed a partial reduction in antibody titer after dithiothreitol treatment, consistent with a predominantly immunoglobulin M antibody, with a possible immunoglobulin G component. The infant and his mother shared the Jk(a - b+) red blood cell phenotype, and maternal antibody screening was negative. In the absence of prior red blood cell exposure or maternal alloimmunization, the antibody was interpreted as naturally occurring. DISCUSSION: This case highlights the importance of recognizing naturally occurring Kidd antibodies in infants to ensure transfusion safety.