Six years' experience performing RHD genotyping to confirm D− red blood cell units in Germany for preventing anti-D immunizations

BACKGROUND: Red blood cell (RBC) units of D+ donors are falsely labeled D− if regular serologic typing fails to detect low D antigen expression or chimerism. The limitations of serology can be overcome by molecular typing.
STUDY DESIGN AND METHODS: In January 2002, we introduced a polymerase chain reaction (PCR)-based assay for RHD as a routine test for first-time donors who typed D− by serologic methods including the indirect antiglobulin test. Samples were tested in pools of 20 for the RHD -specific polymorphism in Intron 4. RHD alleles were identified by PCR and nucleotide sequencing.
RESULTS: Within 6 years, 46,133 serologically D− first-time donors were screened for the RHD gene. The prevalence of RHD gene carriers detected by this method was 0.21 percent. Twenty-three RHD alleles were found of which 15 were new. Approximately one-half of the RHD gene carriers harbored alleles expressing a DEL phenotype resulting in a prevalence of 0.1 percent.
CONCLUSION: The integration of RHD genotyping into the routine screening program was practical. We report 6 years' experience of this donor testing policy, which is not performed in most transfusion services worldwide. RBC units of donors with DEL phenotype have been reported to anti-D immunize D− recipients. We transferred those donors to the D+ donor pool with the rationale of preventing anti-D immunizations, especially dreaded in pregnancies. For each population, it will be necessary to adapt the RHD genotyping strategy to the spectrum of prevalent alleles.