(P-TS-21) Case Report: Use of High-Resolution Genomic Sequencing to Resolve ABO Typing Discrepancy for Kidney Transplantation

It is well established that blood group O and B renal transplant candidates have longer wait times for organs compared to type A and AB patients (~5-6 vs ~2-3 years). Accurate ABO typing is crucial to determine patient eligibility and discrepancies in ABO typing can lead to transplant delays, affecting patient outcomes. In this case, conflicting ABO results between two institutions prompted advanced molecular analysis to resolve the discrepancy for a kidney transplant candidate.

Study

Design/Methods: A retrospective review of ABO typing was conducted for a patient listed for kidney transplant at two institutions. Initial typing at the investigating facility was performed using an automated microwell instrument, followed by conventional tube testing (CTT) in cases with discrepancies. Additional testing to resolve the discrepancy included extended incubation of the front type and anti-A1 antibody testing. The sample was then sent for ABO molecular typing at an Immunohematology Reference Lab (IRL).

Results/Findings:

At investigating institution, the patient typed as O Positive using automated microwell testing on three separate occasions. The United Network of Organ Sharing (UNOS) reported that the patient had been listed as A positive by another institution, leading to the patient's status being changed to 'inactive' on the transplant waitlist. Repeat testing using CTT with incubation confirmed A antigen on the front type and the presence of an anti-A1 antibody. Upon review of preceding samples, it was noted that in the second sample tested, the reaction strength in the A1 cells was 1+; standard policy did not require additional investigation of weaker reaction strengths (below 2+) or inconsistent reaction strengths (difference of >1+ between A1 and B cells). Serology results are reported in Table 1. Medium-resolution molecular testing for common ABO subgroups resulted as probable alleles: ABO*A1.01/ABO*O.02. Given that the observed serologic results were not consistent with these findings, high-resolution genomic sequencing was sent and identified probable alleles: ABO*AW31.02-05/ABO*O.02.01, predicting a Group A weak phenotype. The patient was ultimately listed with UNOS as an A subgroup and received a type A deceased donor kidney.

Conclusions:

This case highlights the importance of thorough evaluation of ABO typing results, including review of weak reactivity and consideration of clinical context to identify and resolve discrepancies. Advanced molecular analysis can provide valuable insights into complex ABO typing cases, facilitating accurate patient classification and organ allocation.