Lab Med Online.  2023 Apr;13(2):103-108. 10.47429/lmo.2023.13.2.103.

An Algorithm to Work-up ABO Subgroups Presenting as Weak B in a Real-world Laboratory: A Case with a Weak B Phenotype Harboring B101/O04-variant Alleles

  • 1Department of Laboratory Medicine, Chonnam National University Hwasun Hospital, Hwasun, Korea
  • 2Department of Prosthodontics, Chonnam National University, Gwangju, Korea
  • 3Department of Laboratory Medicine, Chosun University Hospital, Gwangju, Korea


Weaker ABO subgroups are the main cause of ABO discrepancies, and ABO genotyping studies are crucial to identify them. We performed ABO genotyping to determine the cause of a weak B phenotype in a Korean family, and aimed to develop a practical algorithmic approach to work-up ABO subgroups. ABO genotyping, along with serological ABO typing, was performed on exon 6 and exon 7 sites, sequentially from exon 2 to intron 6, exon 1 and the ABO promoter region, CBF/NF-Y enhancer region, +5.8-kb site in intron 1 using long PCR, and the +22.6-kb enhancer region. A single nucleotide variant (c.579T>C) known to be associated with the O04 allele was observed in exon 7, and an insertion variant (c.203+1622_ 1623insC) was observed in intron 4, which was confirmed to have originated from the O allele using allele-specific sequencing. Based on these results, we made a tentative determination of the O04-variant allele. No remarkable variants were observed at other sites in our study. We were unable to reveal the genetic cause of the weak B phenotype, but detected a new O04-variant allele. This stepwise algorithmic approach to work-up ABO subgroups may be a practical alternative method to whole-genome sequencing.


Weak B; ABO discrepancy; ABO subgroups; ABO genotyping


  • Fig. 1 Summary of our work. (A) The ABO phenotypes and genotypes of the family members with the family tree and table. The ABO phenotypes are indicated below each symbol. The arrow indicates the proband. (B) A stepwise algorithm to work-up the ABO subgroups. (C) Schematic of the genetic targets used to determine ABO genotypes and the ABO phenotypes of all family members and their ABO sequencing results (exons 6 and 7).


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