Investigation into A antigen expression on O-2 heterozygous group O-labeled red blood cell units

BACKGROUND: There are two principal types of group O alleles; deletional alleles feature 261delG leading to nonfunctional truncated protein. Nondeletional alleles have the consensus guanosine at residue 261. The major nondeletional allele, O-2, encodes full-length protein with Gly268Arg. While reports vary, O-2 has been proposed to encode weakly functional A-glycosyltransferase (GTA). The main objective of this study was to evaluate if GTA activity is detectable in O-2 donors. STUDY DESIGN AND METHODS: Donor samples from Pittsburgh and Lund were ABO typed by automated methods. DNA was extracted from 779 group O donors whose red blood cells (RBCs) were available for transfusion. ABO genotyping identified those with O-2 alleles. The following tests were performed on randomly selected O-2 samples (number): adsorption-elution with anti-A (3), flow cytometry (15), plasma enzyme activity (4), and attempts to convert group O RBCs to A (2) with O-2 plasma and titration of plasma anti-A/-A(1) (3). RESULTS: Forty O-2-heterozygous donors were identified (5.1%). Adsorption-elution and sensitive flow cytometry did not reveal A antigens on O-2 RBCs. Plasma enzyme analysis failed to show GTA activity above baseline; O-2 plasma was unable to add measurable A antigens to O RBCs. Titers of anti-A/-A(1) appeared reduced in O-2 plasma but did not cause ABO typing discrepancies. No immediate hemolysis or adverse reactions were reported following transfusion of O-2 RBCs to six evaluable group O recipients. CONCLUSIONS: Other than lower plasma anti-A titers, GTA activity was not found in these O-2 samples. Neither automated blood grouping discrepancies nor clinical problems related to transfusing these O-2 units were observed.