From educational to graded: redefining proficiency testing in ABO genotyping

Aim: ABO genotyping is a valuable tool when serologic typing is inconclusive or not feasible. This study evaluated whether ABO genotyping delivers the same high accuracy and inter-laboratory consistency as serologic methods, and whether a graded proficiency testing (PT) program is warranted for ABO genotyping. We also aimed to determine if molecular ABO typing could be considered for routine use in assigning ABO phenotype in the transplantation setting. Methods: Data including ABO genotype, ABO A subgroup (when applicable), phenotype and method were extracted from participants in the 2023–2025 ABO genotyping PT challenges (n = 55 specimens; 25 ASHI, 30 Southwest Immunodiagnostics). Molecular ABO genotyping was performed in parallel on 53 PT specimens using RT-PCR and NGS to evaluate method concordance. Results: Each PT challenge included 7–15 participating laboratories. Of the 55 specimens, 52 (95%) reached 100% phenotype consensus. RT-PCR and NGS results were highly concordant, with only one phenotype discrepancy (Aw vs A2). Six novel O alleles were identified in 9 specimens. Conclusion: Despite limitations such as incomplete gene coverage and lack of standardized references, ABO genotyping achieved 100% phenotype prediction accuracy in this PT study. These findings demonstrate that PT programs provide a robust framework for assessing and monitoring the analytical performance of ABO genotyping assays as laboratories increasingly adopt this technology for clinical transplantation testing.