The Blood Group A Genotype Determines the Level of Expression of the Blood Group A on Platelets But Not the Anti-B Isotiter

Background: The extent of expression of the blood group A on platelets is controversial. Further, the relation between platelets' blood group A expression and the titers of isoagglutinins has not been thoroughly investigated, so far. Methods: We evaluated the relation between the genotype with platelets' blood group A and H expression estimated by flow cytometry and the titers of isoagglutinins. Results: The A expression varied between genotypes and within genotypes. However, the expression in A₁ was stronger than in all other genotypes (p < 0.0001). An overlap of expression levels was apparent between homozygous A₁A₁ and heterozygous A₁ individuals. Still, The A₁A₁ genotype is associated with a particularly high antigen expression (p = 0.009). Platelets' A expression in A₂ versus blood group O donors was also significant (p = 0.007), but there was again an overlap of expression. The secretor status had only little influence on the expression (p = 0.18). Also, isoagglutinin titers were not associated with genotypes. Conclusion: To distinguish between A₁ and A₂ donors may reduce incompatible platelet transfusions and therefore be favorable on platelet transfusion increment. Clinical data are needed to support this notion.