Abstract: Objective To identify the precise ABO blood type subgroup with gene sequencing and discuss the relationship between the serology and genotype in CisAB / B blood subgroup. Methods We screened ABO blood type of blood donors in the blood center. Samples were first examined with a routine serological method. Those with ambiguous results were further examined with genotyping to identify ABO subgroups. The exon 6, exon 7 and the flanking region of ABO gene as well as its promoter and enhancer region were sequenced by PCR. Mutations found in the PCR were further confirmed by haplotype sequencing method. Results Genotype of the two cases were both CisAB01 / B101. Serological test showed the two cases to be A2B and AxB subgroup. Sequences of the promoter region and enhancer region of the two cases were the same. Conclusion It is difficult to identify CisAB only by serological method. DNA sequencing combined with serological testing is able to precisely identify ABO blood subgroup. Individuals with the same genotype would show different serological characteristics.

Key words: CisAB, ABO blood subgroup, sequencing