The prevalence of alloantibodies and ABO RhD blood groups in a cohort of Aboriginal and non-Aboriginal cardiac surgery patients from Australia

Introduction
Limited evidence exists on the distribution of ABO RhD blood groups and prevalence and specificity of red cell (RBC) alloantibodies in Aboriginal and Torres Strait Islander peoples of Australia. We investigated RBC alloantibody prevalence and ABO RhD groups in Aboriginal patients undergoing cardiac surgery at a South Australian (SA) tertiary hospital, a major cardiac surgical referral centre for Northern Territory (NT) patients

Methods
Retrospective analysis of all consecutive patients undergoing cardiac surgery at Flinders Medical Centre (FMC) between January 2014 and June 2019. ABO and RhD blood groups, and RBC alloantibody prevalence, specificity, and clinical significance in Aboriginal and non-Aboriginal cardiac patients were determined at time of surgery and on follow up to 2021.

Results
2327 patients were included, 588 (25.3%) were from NT, and 420 (18.0%) were Aboriginal. Aboriginal patients had a higher prevalence of ABO group O (59.8% vs 43.9%) and RhD positive (99.0% vs 83.8%). One-hundred-and-eleven patients had 154 RBC alloantibodies, 57/420 (13.6%) Aboriginal versus 54/1907 (2.8%) non-Aboriginal (p<0.0001). There were higher numbers of IgM alloantibodies in Aboriginal patients (59/77, 77%), with Lewis, P1 and M more common. Sixty patients had antibodies detected at time of surgery, 14 NT patients with previously detected alloantibodies, prior to surgery, presented with a negative antibody screen and 37 had new antibodies detected after cardiac surgery.

Conclusion
A high prevalence of IgM alloantibodies was found in Aboriginal compared to non-Aboriginal cardiac surgery patients. The clinical significance of these IgM alloantibodies in Aboriginal peoples requires further investigation.