Deceased donor ABO discrepancy due to a rare AwB subgroup: Implications for organ allocation

Accurate ABO determination is critical for safe deceased donor organ allocation. Weak or variant ABO subgroups may not be reliably detected by routine serologic testing, especially under urgent conditions or following transfusion. Such limitations can result in discrepant ABO assignments with potential implications for transplant safety.

We describe a deceased organ donor with discordant ABO typing results reported by two laboratories. Serologic testing was performed using gel agglutination methods on independently collected specimens. Due to persistent discrepancies, ABO genotyping was performed using real-time polymerase chain reaction to resolve the donor's blood group.

Initial serologic testing identified the donor as AB RhD+ at one laboratory, while a second laboratory reported B RhD+ results. Repeat serologic evaluation demonstrated weak and variable A antigen reactivity, suggestive of a weak A subgroup. Molecular genotyping performed on specimens from both laboratories identified an AwB genotype, confirming the presence of a weak A allele. Because molecular results were not available prior to organ allocation and the discrepancy could not be resolved in real time, the donor was conservatively classified as AB for allocation purposes.

This case highlights the vulnerability of routine serologic testing to misclassification of rare weak ABO subgroups. Integration of molecular genotyping with serologic testing can provide resolution of ABO discrepancies and enhance transplant safety. This case demonstrates a policy-relevant gap in current ABO determination workflows for deceased donors. Lack of standardized inter-laboratory data sharing and limited access to rapid molecular testing may unnecessarily restrict organ utilization.