Aim: Accurate blood typing is critical for the distribution of solid organs. The aim of this study was to assess the utility of next generation sequencing (NGS) with ABO hybrid capture probes to predict serologic ABO typing in the setting of solid organ transplantation.
Methods: Blood samples from 2884 sequential renal transplant candidates, living donors and deceased donors were ABO typed by standard serologic techniques between August 2023 and April 2024. The same samples were HLA high resolution typed by NGS using AlloSeqTx17 spiked with ABO probes provided by CareDx and analyzed with AlloSeq Assign software. The ABO probes were designed to sequence exons 2 to 7 and the flanking intronic sequences.
Results: The relative representation of the four ABO groups, by standard serological methods, in this primarily Florida-based population is: O (50%), A (33%), B (15%), AB (2%) and indeterminate ( <1%). Fifty-seven percent of these samples typed to unambiguous International Society of Blood Transfusions (ISBT) recognized alleles. Another 31% of samples had ambiguous results, with most ambiguities in exon 1, followed by exon 7. Assign software predicted serologic equivalents for these two groups of samples (N=2535) that were highly concordant with serologic ABO typing (99.17%). A total of 21 samples were discrepant. Eighteen of these samples (86%) were serologically indeterminate due to hemodilution, mixed field or discordant forward/reverse type. The serological and NGS assigned ABO types for the remaining three samples were conflicting, O vs AW.13, O.02.02, B vs BA.03 and A vs O.01.01 (still under investigation). The remaining 12% of all samples had mismatches to ISBT recognized alleles. Interestingly, the serologic equivalent could be predicted with high frequency for these mismatch samples. However, this translation is not provided by AlloSeq Assign software and thus cannot be easily ported to a LIMS system via interface. A1 and A2 subtyping was performed on 147 donor samples, 76% were A1, while the remaining 24% were A2. There was no obvious correlation between genotype and A subtype.
Conclusion: ABO genotyping by NGS is highly concordant with serologic ABO typing. The current utility of ABO genotyping is limited primarily by the number of ISBT cataloged allele sequences with phenotypic information.
