Ann Lab Med 2019; 39(2): 115-120
Cis-AB, the Blood Group of Many Faces, Is a Conundrum to the Novice Eye
Sejong Chun, M.D.1,*, Sooin Choi, M.D.2,*, HongBi Yu, B.S.3, and Duck Cho, M.D.3,4
1Department of Laboratory Medicine, Chonnam National University Medical School & Hospital, Gwangju, Korea; 2Department of Laboratory Medicine, Soonchunhyang University Hospital Cheonan, Soonchunhyang University College of Medicine, Cheonan, Korea; 3Department of Health Sciences and Technology, Samsung Advanced Institute for Health Sciences and Technology, Sungkyunkwan University, Seoul, Korea; 4Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
Corresponding author: Duck Cho, M.D.
Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 06351, Korea
Tel: +82-2-3410-2403
Fax: +82-2-3410-2719
*These authors contributed equally to this work.
Received: April 3, 2018; Revised: July 9, 2018; Accepted: October 22, 2018; Published online: March 1, 2019.
© Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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, cis-AB, Genotyping, Serology

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