RHD DNA screening for weak D, DEL and D+/– 'chimeras'

DNA-based methods in the immunohematology reference laboratory

Although hemagglutination serves the immunohematology reference laboratory well, when used alone, it has limited capability to resolve complex problems. This overview discusses how molecular approaches can be used in the immunohematology reference laboratory. In order to apply molecular approaches to immunohematology, knowledge of genes, DNA-based methods, and the molecular bases of blood groups are required. When applied correctly, DNA-based methods can predict blood groups to resolve ABO/Rh discrepancies, identify variant alleles, and screen donors for antigen-negative units. DNA-based testing in immunohematology is a valuable tool used to resolve blood group incompatibilities and to support patients in their transfusion needs.

Effective molecular RHD typing strategy for blood donations

BACKGROUND

More than 50 weak D alleles and numerous partial D alleles have been described to date that can be identified by molecular methods as polymerase chain reaction (PCR) and DNA sequencing of the RHD gene. A real time-based RHD typing scheme was developed and tested during an 8-month period.

STUDY DESIGN AND METHODS

A total of 53,347 blood donors and patients were tested with standardized immunohematologic methods. A total of 201 DNA samples with weak D reactions underwent molecular characterization by weak D real-time PCR, exon-screening real-time PCR, and nucleotide sequencing of RHD Exons 1 through 10. A total of 2,427 samples with D- phenotype were tested for the presence of RHD markers.

RESULTS

Molecular typing of 201 samples with weak D expression revealed 15 different known aberrant alleles as well as one new weak D type dubbed weak D Type 49. Approximately 60 percent of the alleles were determined as weak D Types 1 through 3 and detected by only one amplification run. Weak D Type 1 represented the most frequent allele (n = 72). Three samples with D- phenotype showed amplification of RHD-specific markers. Sequence-based typing (SBT) of these samples revealed a DEL allele, RHD(IVS3+1G>A), in two samples and one weak D Type 4.3.

CONCLUSIONS

The presented scheme for RHD genotyping of weak D red blood cell units was reliable for detection of aberrant alleles. Testing of D- blood samples as quality control seems to overcome limitations of standard serology by detection of samples with weak D or DEL phenotype.