Abstract: Objective By integrating serological characteristics with gene sequencing analysis, the aim is to clarify the chimeric nature of a difficult ABO blood type sample presenting mixed field agglutination and to identify its specific ABO allele combination, thereby assisting in formulating precise blood transfusion strategies. Methods Microcolumn gel immunotechnology was used for typing and irregular antibody screening, and blood typing was rechecked by the tube saline method. Polymerase chain reaction (PCR) was used to target amplify the 6th and 7th exons of the ABO gene and their flanking intron regions, and Sanger sequencing technology was used for allele typing and single nucleotide polymorphism (SNP) analysis. Results Based on the serological MFA and the sequencing results of exons 6 and 7, it is suggested that the patient may have A1/O1/O2 chimerism (chimerism ratio at the c.261delG site is 1∶5). Conclusion For samples with MAF, even if only partial genetic testing is performed, the analysis of key loci can still provide an important reference for transfusion.

Key words: Blood group chimera, Serological phenotype, Genotype, Single nucleotide polymorphism