Uncommon RHD variants and an unconventional RHCE hybrid allele with D epitope expression in blood donors from...

Some D variants, especially those expressed by hybrid alleles, can react falsely negative in routine serology tests. Recently, an increasing number of facilities have strived to implement a method for RHD molecular screening in blood donors.

The participants in this two-year prospective study were 735 unrelated voluntary blood donors from northwestern Croatia. Blood donors were individually tested for RHD sequences by qPCR. In reactive samples, D antigen was confirmed by adsorption/elution.

RHD screening was performed by examination of RHD exons 3, 5, and 10 in 589/704 (83.7%) serologically D-negative ccee samples, all being negative. Serology results of the Rh phenotype (C+ and/or E+) were confirmed by qPCR in the remaining 115 donors (16.3%). In this group, 112 donors were RHD-negative. RHD DEL alleles were determined in two Ccee donors (0.28%): RHD*DEL32 and RHD*DEL44. One donor (0.14%) was homozygous for RHD deletion but revealed an RHD sequence in 5'-UTR within the RHCE locus, c.-132A. All three donors with Rh variants expressed D epitopes as displayed by adsorption/elution. The serologically weak D group (31 participants) contained seven RHD alleles.

This study reports the DEL phenotype of RHD*DEL44 expression. The hybrid allele RHCE*D(1)-CE was described previously, but here we illustrate the presence of D epitope(s) in a donor with homozygous RHD deletion. Weak D type 40 haplotype association was elucidated. Blood donor molecular Rh testing can prevent the immunization of genuine D-negative patients by D-positive units that reacted negatively in routine serological testing.