Clinical significances and distribution of unexpected antibodies found in infants

The unexpected antibody test is an essential for ensuring the safety of blood transfusions. In infants, different pre-transfusion tests and transfusion strategies are needed due to their immature antigen/antibody system. This study aims to analyze the pattern of unexpected antibodies and their clinical significance in infants.A retrospective analysis was conducted on the results of unexpected antibody identification tests performed on infants under one year of age at Asan Medical Center from 1999 to 2022. Patients' unexpected antibody identification test results and clinical information were investigated. The results of unexpected antibody identification and phenotype of each patient's mother were collected.45 cases of antibody results were studied. 25 cases were found in infants under 4 months of age, and 18 cases (76%) were associated with hemolytic disease of the fetus and newborn (HDFN). The most common unexpected antibody in infants was anti-M (17 cases). There was one case of severe HDFN caused by anti-M. In 10 cases, anti-E and anti-c were found together, and 9 of these cases were associated with HDFN. There were four cases with a history of previous transfusion.Non-ABO antibodies found in infants showed a different pattern compared to adults. Interpreting unexpected antibody tests in infants, it is important to consider the clinical status of the infant and the test results of the mother, due to possibility of HDFN. To our knowledge, this is the first study to reveal the distribution and clinical significances of unexpected antibodies found in infants in Korea.