Background: The SMIM1 protein carries the Vel blood group antigen, and homozygosity for a 17 bp deletion in the coding region of the SMIM1 gene represents the molecular basis of the Vel- blood group phenotype. We developed PCR-based methods for typing the SMIM1 17 bp (64-80del) gene deletion and performed a molecular screening for the Vel- blood type in German blood donors. Methods: For SMIM1 genotyping, TaqMan-PCR and PCR-SSP methods were developed and validated using reference samples. Both methods were used for screening of donors with blood group O from southwestern Germany. Heterozygotes and homozygotes for the SMIM1 64-80del allele were serologically typed for the Vel blood group antigen. In addition, the rs1175550 SNP in SMIM1 was typed and correlated to the results of the phenotyping. Results: Both genotyping methods, TaqMan-PCR and PCR-SSP, represent reliable methods for the detection of the SMIM1 64-80del allele. Screening of 10,598 blood group O donors revealed 5 individuals homozygous for the deletional allele. They were confirmed Vel- by serological typing. Heterozygotes for the 64-80del allele showed different antigen expressions ranging from very weak to regular positive. Conclusion: Molecular screening of blood donors for the Vel- blood type is feasible and avoids the limitations of serological typing which might show false-negative results with heterozygous individuals. The identification of Vel- blood donors significantly contributes to the adequate blood supply of patients with anti-Vel.

Background: The detection and identification of antibodies to red blood cell (RBC) antigens is one of the most important and challenging issues in transfusion medicine. Up to date there are 354 RBC antigens recognized by the International Society of Blood Transfusion (ISBT). The reagent RBCs used in commercial antibody screening and identification panels however are usually serologically typed for up to 40 clinically important antigens. Thus the identification of many antibody specificities remains impossible when using reagent RBCs with only limited information about their antigens. To improve the pre-transfusion diagnostics, we developed antibody identification panels with reagent RBCs serologically typed for 26 antigens and additionally genotyped for 30 blood group alleles. Methods: The reagent RBCs in the panels were characterized serologically for the clinically most significant ‘standard' antigens. The reagent RBC donors were additionally genotyped by using in-house PCR-SSP methods. The antibody identification was performed in the indirect antiglobulin test using untreated and papain-treated RBCs in the gel technique. Antibodies identified due to the genotype information were confirmed by serology using appropriate reference RBCs. Results: Within a time period of 3 years and 8 months, 16,878 blood samples from 8,467 patients were tested in our reference laboratory. In total, 21 different antibodies from 10 different blood group systems could be identified in 126 patients (1.5%) due to the genotype information obtained for the reagent RBCs. Antibodies to antigens from the Knops system (53 patients; 42%, 8 patients with anti-Kn^b) and to Cartwright antigens (31 patients; 25%) were the most frequent. Conclusion: The use of genotyped reagent RBCs in antibody identification panels extends the range of detectable antibody specificities, accelerates the antibody identification, and improves the pre-transfusion diagnostics.

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