Identification of RHD alleles with the potential of anti-D immunization among seemingly D- blood donors in Upper Austria

BACKGROUND: Aberrant RHD alleles leading to a reduced expression of D antigen on the red blood cell (RBC) surface may be mistyped as D- by serology. To quantify the occurrence of weak D, DEL, and D+/- chimera among apparent D- first-time blood donors, polymerase chain reaction (PCR) screening was implemented as a routine service.

STUDY DESIGN AND METHODS: A total of 23,330 pretyped D- samples were tested for RHD markers in Exons 4, 7, and 10 in pools of 20 by PCR. Samples with positive results in PCR were reevaluated by exon-specific PCRs, DNA sequencing, and serologic methods.

RESULTS: Among 94 PCR-positive samples, 74 exhibited a weak D or DEL phenotype, dubbed weak D type 1, weak D type 2, weak D type 5, weak D type 32, weak D type 4.3, RHD(M295I), RHD(del147), and RHD(1227G>A). The most prevalent alleles were weak D type 4.3 (n = 31) and RHD(IVS3+1G>A) (n = 24).

CONCLUSIONS: As a clinical consequence, 74 blood donor samples carrying weak D and DEL phenotypes with the potential of causing secondary immunizations in recipients were reclassified as D+. Those samples were reliably amplified by RHD Exon 7 PCR; therefore, its usage in the Upper Austrian population is recommended. The association of the weak D type 4.3 samples with a ce leads to the policy that all apparently D- donors should be tested with genotyping methods; otherwise, potentially immunogenic RHD alleles may be overseen.