[Resolution of ABO Discrepancies by ABO Genotyping.]

Before a blood transfusion, both red cell and serum typing need to be matched for ABO tests on the donor and patient (recipient). When a mismatch exists in the tests, additional ABO genotyping and serological tests are required for the resolution of the discrepancy. We performed ABO genotyping on a series of blood donors and patients with ABO discrepancies to assist in resolving their blood groups.

We examined 46 samples with ABO discrepancies from a random pool of donors recruited at Gwangju-Chonnam Red Cross Blood Center and from patients at Chonnam National University Hospital between May 2004 and July 2005. ABO genotyping was performed on all samples with an allele specific polymerase chain reaction for differentiation of A, B,O, cis-AB, A(var) (784 G>A), and B(var) (547 G>A) alleles; routine serologic tests were also performed. Exon 6 and 7 of ABO gene from five samples were sequenced.

The genotypes of 18 donors/patients with weakened A or B antigen expressions consisted of 4 cases of cis-AB/O (3 A(2)B(3), 1 A(2)B); 5 cases of cis-AB/A (5 A(1)B(x or el)); 2 cases of A/O (1 O, 1 A(m or x)); 1 case of B/O (1 B(m or x)); 4 cases of A/B (1 A(2)B , 1 A(1)B(x or el), 2 A(1)B(3)); and 2 cases of A(var)/B (2 A(w)B). On the other hand, the genotypes of 28 samples with unexpected serum reactions included 18 cases of A/O (16 A(1), 2 A(int)); 7 cases of A/A (5 A(1), 1 A(1)B(x or el), 1 A(1)B(w)); and 3 cases of O/O (1 O, 2 B(w)).

ABO genotyping is useful for differentiating the ABO discrepancies that were difficult to resolve by serological tests. The most frequent unusual red cell reactions were weak A and B antigen expressions, which were resulted from the ABO subgroup alleles including cis-AB allele, whereas the most frequent unusual serum reactions were caused by decreased anti-B titers.