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The article presents questions and answers related to red blood cells for patients who are negative for a high-frequency antigen including the definition of a rare donor, problems encountered in finding compatible red blood cells (RBC) for patients, and whether countries have a national panel of rare donors and/or a national bank of frozen (RBC) units from such donors.

Background and Objectives The Duffy ( FY) blood group system is controlled by four major alleles: FY*A and FY*B, the Caucasian common alleles, encoding Fya and Fyb antigens; FY*X allele responsible for a poorly expressed Fyb antigen, and FY*Fy a silent predominant allele among Black population. Despite the recent development of a real-time fluorescent polymerase chain reaction (PCR) method for FY genotyping FY*X genotyping has not been described by this method. This study focused on the real-time FY*X genotyping development associated with a complete, one-step real-time FY genotyping, based on fluorescence resonance energy transfer (FRET) technology. Materials and Methods Seventy-two blood samples from Fy(a+b–) Caucasian blood donors were studied by real-time PCR only. Forty-seven Caucasian and Black individual blood samples, referred to our laboratory, were studied by PCR-RFLP and real-time PCR. For each individual, the result of the genotype was compared to the known phenotype. Results The FY*X allele frequency calculated in an Fy(a+b–) Caucasian blood donors population was 0·014. With the Caucasian and Black patient samples we found a complete correlation between PCR-RFLP and the real-time PCR method whatever the alleles combination tested. When the known phenotype was not correlated to FY*X genotype, the presence of the Fyb antigen was always confirmed by adsorption–elution. Conclusion The real-time technology method is rapid and accurate for FY genotyping. From now, we are able to detect the FY*X allele in all the alleles combinations studied. Regarding its significant frequency, the detection of the FY*X allele is useful for the correct typing of blood donors and recipients considering the therapeutic use of blood units and the preparation of test red blood cells for antibody screening. [ABSTRACT FROM AUTHOR]