Molecular basis of serological weak D phenotypes and RhD typing discrepancies identified in the Korean population

Abstract

Background: The molecular basis of RhD blood groups differs with race/ethnicity. This study aimed to investigate the molecular basis of serological weak D phenotypes and RhD typing discrepancies in the Korean population.

Materials and methods: The RhD status of 188,852 Korean patients was initially determined using the automated microplate method and manual tile method. In case of no agglutination, weak D testing was further performed using the tube and gel methods. Serologically D-negative samples with C+ and/or E+ were tested using polymerase chain reaction-sequence specific primers for four RHD targets and/or exon 9 sequencing. Samples showing a serological weak D phenotype or an RhD typing discrepancy were subjected to full RHD gene sequencing.

Results: Of the 32 samples showing a serological weak D phenotype and 191 samples showing a serologically D-negative phenotype with C+ and/or E+, 23 and 50 were genotyped, respectively. Among the weak D samples, the most common alleles were RHD*15 (n=6), RHD*13.01 (n=4), and RHD*01W.25 (n=4), and no variant was found in two samples. RHD*01EL.01 (n=26) accounted for more than half of the D-negative samples. Of the seven samples that were typed as D-positive using the automated microplate method but showed weak reactivity using the tile method, four were genotyped, and the results were as follows: RHD*01W.33 (n=2), RHD*01W.43 (n=1), and no variant found (n=1).

Discussion: In our cohort, various D variant alleles including RHD*15 were identified; however, RHD*01W.1, RHD*01W.2, RHD*01W.3, RHD*09.03.01, and RHD*09.04, accounting for more than 95% of Caucasians with a serological weak D phenotype, were not found. Our study reaffirms that the distribution of D variant alleles differs between East Asians and Caucasians. Our findings also indicate that some D variants including RHD*01W.33 and RHD*01W.43 are at risk of being mistyped as D-positive by a highly sensitive RhD typing method such as an automated microplate method.

Figure 1. RhD typing strategy recommended for East Asian patients

Under this strategy, East Asian patients are tested by RHD genotyping when weak reactivity or discordant results are observed in direct agglutination testing. As previously suggested by our group, D-negative East Asian patients carrying a C+ and/or E+ phenotype are tested by RHD genotyping. Patients are classified and managed as D-positive when the RHD*01EL.01 allele is detected by RHD genotyping. ^*The definition of weak reactivity can vary from laboratory to laboratory, depending on the serological method and anti-D reagent used for direct agglutination testing.