Mixed-field agglutination observed in column agglutination testing is not always associated with the A3 subgroup.

Mixed-field agglutination (MFA) can be observed in forward typing of samples from A3 individuals with serologic ABO typing methods. The results of column agglutination testing (CAT) and tube agglutination testing using different antibody clones can be discordant. In this report, we reveal our experience using polymerase chain reaction-sequence-based typing (PCR-SBT) of ABO exon 7 to clarify serologic method discordance of A subgroup blood typing in Northern Thai donors.