Abstract: Objective To investigate the characters of B(A)04 subtype in order to provide a theoretical basis for the work of clinical blood transfusion. Methods The characteristics of B(A)04 subtype were identified by serological and genotyping technology. Exons 1-7 and adjacent introns of the ABO gene were amplified by polymerase chain reaction (PCR). The PCR products were directly sequenced and cloning sequenced to identify the molecular mechanism of B(A)04 subtype. Results The patient showed ABO forward and reverse typing discrepancy. ABO forward typing defined A weak B. However, A1 cells (2+) and B cells (-) were observed in the reverse typing. The ABO gene sequencing showed a A>G substitution at position in exon 7 which caused a Met to Val exchange at codon 214. The ABO blood group genotype was ABO*B(A)04/O01. Conclusion The identification and analysis of subordinate or rare blood types should be very careful. In order to ensure the safety of blood transfusion, the molecular biological detection should carried out when necessary.

Key words: ABO blood group, B(A) subgroup, ABO gene, ABO genotype