Red Blood Cell and Platelet Genotyping: from Current Practice to Future High-Throughput Donor Typing

The molecular basis of almost all red cell and platelet blood group antigens is known. This enables the prediction of red cell or platelet phenotypes based upon the genotypes. In many laboratories, blood group genotyping assays are routinely used in cases where patient red cells cannot be used for serological typing due to the presence of autoantibodies (direct antiglobulin test (DAT)-positive) or after recent transfusion. Furthermore, fetal genotyping is routinely performed where there is a risk of alloimmune-mediated red cell or platelet destruction. In the Netherlands, medium-throughput human platelet antigen (HPA) genotyping has been introduced in the blood banks to guarantee direct (on-shelf) availability of HPA-1a- and HPA-5b-negative platelets for newborns suffering from neonatal alloimmune thrombocytopenia. The techniques used, pyrosequencing and Taq- Man-based allele-specific hybridization assay, are discussed in this review. Recently, several research groups investigated whether red cell molecular typing could also be introduced for large-scale blood donor typing to obtain and maintain an inventory of typed (antigen-negative) donors. The reason for this is that phenotyping of large cohorts of donors is a labor-intensive exercise and hampered by the lack of sufficient amounts of approved typing reagents for all blood group systems of interest. Several approaches for high-throughput genotyping, based on DNA microarrays spotted on glass slides or beads, have now been tested and are also discussed in this review.