Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 39 (2), 115-120

Cis-AB, the Blood Group of Many Faces, Is a Conundrum to the Novice Eye


Cis-AB, the Blood Group of Many Faces, Is a Conundrum to the Novice Eye

Sejong Chun et al. Ann Lab Med.


Cis-AB, a rare ABO variant, is caused by a gene mutation that results in a single glycosyltransferase enzyme with dual A and B glycosyltransferase activities. It is the most frequent ABO subgroup in Korea, and it occurs more frequently in the East Asian region than in the rest of the world. The typical phenotype of cis-AB is A₂B₃, but it can express various phenotypes when paired with an A or B allele, which can lead to misclassification in the ABO grouping and consequently to adverse hemolytic transfusion reactions. While cis-AB was first discovered as having an unusual inheritance pattern, it was later found that both A and B antigens are expressed from the same allele inherited from a single parent; hence, the name cis-AB. Earlier studies relied on serological and familial investigation of cis-AB subjects, but its detection has become much easier with the introduction of molecular methods. This review will summarize the serological variety, genetic basis and inheritance pattern, laboratory methods of investigation, clinical significance, and the blood type of choice for transfusion for the cis-AB blood group.

Keywords: ABO; Genotyping; Serology; cis-AB.

Conflict of interest statement

The authors have no conflicts of interest to declare.


Fig. 1
Fig. 1. Three representative Korean cis-AB family cases illustrating cis-AB inheritance of the ABO blood group depending on the mother's genotype (O/O; Family 1, A/O; Family 2, and B/O; Family 3). The ABO phenotype and genotype of each person are shown.

Similar articles

See all similar articles


    1. Blumenfeld OO, Patnaik SK. Allelic genes of blood group antigens: a source of human mutations and cSNPs documented in the Blood Group Antigen Gene Mutation Database. Hum Mutat. 2004;23:8–16. - PubMed
    1. Olsson ML, Irshaid NM, Hosseini-Maaf B, Hellberg A, Moulds MK, Sareneva H, et al. Genomic analysis of clinical samples with serologic ABO blood grouping discrepancies: identification of 15 novel A and B subgroup alleles. Blood. 2001;98:1585–1593. - PubMed
    1. Cai X, Jin S, Liu X, Fan L, Lu Q, Wang J, et al. Molecular genetic analysis of ABO blood group variations reveals 29 novel ABO subgroup alleles. Transfusion. 2013;53:2910–2916. - PubMed
    1. Ogasawara K, Yabe R, Uchikawa M, Saitou N, Bannai M, Nakata K, et al. Molecular genetic analysis of variant phenotypes of the ABO blood group system. Blood. 1996;88:2732–2737. - PubMed
    1. Cho D, Kim SH, Jeon MJ, Choi KL, Kee SJ, Shin MG, et al. The serological and genetic basis of the cis-AB blood group in Korea. Vox Sang. 2004;87:41–43. - PubMed