OA1-AM24-TU-15 - ABO*AW.09 is a common ABO subgroup involved in ABO discrepancies in US patients and blood donors

A discrepancy between forward and reverse ABO grouping may be indicative of the presence of an ABO subgroup. ABO genotyping can detect ABO gene variants associated with altered or weakened antigen expression. After implementing a medium-resolution ABO genotyping panel, cases submitted for ABO genotyping due to ABO typing discrepancy were examined. Demographic and serologic information was reviewed for cases in which the ABO*AW.09 allele was identified.

Study

Design/Methods: Peripheral blood samples received for ABO genotyping during an 11-month period (May 15, 2023 to April 15, 2024) were reviewed. DNA was extracted and tested using RBC FluoGeneNX ABO plus (inno-train Diagnostik GmbH). This medium-resolution genotyping panel interrogates 25 markers, both single nucleotide variants and insertion/deletion polymorphisms, to predict ABO alleles. ABO allele assignments were assessed and those predicted to carry ABO*AW.09 based on presence of ABO c.46G >A and c.1061delC were further examined for subject type (donor or patient), race/ethnicity and reported serologic results.

Results/Findings: During the study period, 180 cases (138 patients, 38 blood donors and 4 tissue donors) were submitted for ABO genotyping to resolve a typing discrepancy. Of these, 77 (43%) were predicted to carry an ABO subgroup and 2 yielded “no type determined" (NTD). The most common subgroups were A2, found in 40 (22%), AW.09, found in 17 (9%) and AEL, found in 9 (5%) of cases (see Table).  Of the two patient cases that yielded NTD, one carried c.46A in the absence of c.1061delC. Of the cases with ABO*AW.09, 10 (59%) were reported to be of African descent, 4 (23%) “other” race, 1 (6%) Caucasian, 1 (6%) mixed race, and 1 (6%) race was not provided. Of the samples with ABO*AW.09, 15 were patients and 2 were donors. In 13 of the 17 cases (76%), the ABO*AW.09 was co-inherited with ABO*B.01. Five of the 17 cases (29%) were reported to exhibit mixed field with anti-A. Four cases (24%) were reported to have no reactivity with A1 lectin. In two cases (12%), anti-A1 was reported. 

Conclusions: Variant ABO alleles were found in 44% of samples submitted to a US national molecular immunohematology reference laboratory for ABO genotyping for resolution of typing discrepancies. Not surprisingly, ABO*A2 was the most identified variant allele. ABO*AW.09 was the second most detected variant allele. The peer-reviewed literature has little information about the serologic presentation of samples with ABO*AW.09. This study demonstrates that samples with the ABO*AW.09 allele can present with mixed field reactivity with anti-A, show no reactivity with anti-A1 lectin and may present with anti-A1.