Characteristics and frequency of DEL phenotype detected by indirect antiglobulin test in Dalmatia county of Croatia

Rh flow cytometry: An updated methodology for D antigen density applied to weak D types 164 and 165

BACKGROUND

An original methodology for determining the D antigen density on red cells was published in 2000 and has been applied in many publications since. This flow cytometry-based assay remained largely unrevised utilizing monoclonal anti-Ds that are not readily available anymore. We updated the methodology to quantify erythrocyte D antigen sites using microspheres and monoclonal anti-Ds that are commercially available today.

METHODS

The absolute D antigen density of a frozen standard CcDEe cell, drawn in 2003, a fresh blood donation from the same individual, drawn in 2022, and an internal control CcDEe cell, was quantified by flow cytometry using fluorescence-labeled microspheres. The internal control CcDEe cell was used in conjunction with 9 commercial anti-Ds to determine D antigen densities of 7 normal D, 4 partial D, and 11 weak D type samples, including 2 novel alleles.

RESULTS

The reproducibility of the updated assay was evaluated with red cells of published D antigen densities. The current results matched the known ones closely. The new weak D types 164 and 165 carried 4500 and 1505 D antigens/red cell, respectively. The absolute D antigen density decreased from 27,231 to 26,037 in an individual over 19 years.

DISCUSSION

The updated assay gave highly reproducible results for the D antigen densities of Rh phenotypes. Readily available anti-Ds allowed for the determination of the D antigen densities of 7 weak D types. The assay is suitable to evaluate the effects of distinct amino acid substitutions on the RhD phenotype.

Application of Multiplex Ligation-Dependent Probe Amplification Assay for Genotyping Major Blood Group Systems Including DEL Variants in the D-Negative Korean Population

Background

The DEL blood type, a very weak D variant, is a major concern in the field of transfusion medicine because of its potential to cause anti-D alloimmunization. We investigated the molecular basis of serologically D-negative phenotypes, including the DEL type, and the distribution of other blood group systems in the Korean population using the recently developed multiplex ligation-dependent probe amplification (MLPA) assay.

Methods

Blood group genotyping using the MLPA assay and RhCE phenotyping were performed on randomly selected 95 D-negative red blood cell products. The MLPA results were verified by multiplex PCR for the RHD promoter, exons 4, 7, and 10 and by direct sequencing of RHD exon 9.

Results

Out of 95 cases, total deletion of the RHD was observed in 74 cases (77.9%) and four cases (4.2%) had an RHD-CE-D hybrid allele. The other 17 cases (17.9%) had an RHD(1227G>A) allele, which was further confirmed by sequencing analysis. The RhCE phenotypes of RHD(1227G>A) alleles were composed of 14 Cce and 3 CcEe, and all 60 cases of the ce phenotype were revealed to have a total deletion of the RHD. Genotyping results and allele distribution of the other 17 blood group systems were consistent with previous reports on the East Asian population.

Conclusions

MLPA assay correctly determined RHD genotype, including RHD-CE-D hybrid alleles or RHD(1227G>A) allele, and other clinically relevant blood group genotypes in D-negative Koreans. The use of MLPA assay on serologically D-negative individuals may help improve transfusion safety by preventing anti-D alloimmunization.

Anti-D reagents should be chosen accordingly to the prevalence of D variants in the obstetric population

BACKGROUND

Resolving ambiguous results of D antigen typing is crucial for appropriate and rational administration of anti-D immunoprophylaxis and transfusion practice in obstetric population. The aim of the study was to establish selection criteria of anti-D reagents for our population.

METHODS

A total of 12 689 samples from primiparous women in Split-Dalmatia County, Croatia, were typed for RhD antigen during the period of 5 years. Ambiguous results were submitted to additional serologic investigation and genotyping. RHD genotyping was performed by commercial genotyping kits (Ready Gene weak D ^® and Ready gene CDE, Inno-Train, Kronberg, Germany). Relative frequencies and accompanying 95% confidence intervals were used to estimate the prevalence of variants.

RESULTS

The prevalence of D variants was 0.42% (95% CI 0.31; 0.53). The most common partial D variant was D Va (RHD*05.05), with the prevalence of 0.08% (95% CI 0.03; 0.13). All weak D variants were weak D types 1, 2 and 3 (RHD*weak D type 1, RHD*weak D type 2, RHD*weak D type 3). Weak D samples were distinguishable from partial D in routine typing due to the difference in reactivity of partial D samples with clones D7B8 and RUM-1. Cell line RUM-1 gives weak or negative reactions with partial DVa category.

CONCLUSION

The most common partial D variant in our population is DVa. It is recommended to use cell lines which do not strongly agglutinate DVa variant in routine RhD typing. The appropriate choice of reagents will enable the serology methods to recognize the cases in which RHD genotyping is required.

Screening for DEL phenotype in RhD negative Indians

BACKGROUND

DEL phenotype represents a very weak form of D variant detected only by adsorption and elution technique. DEL phenotype individuals mistyped as RhD-negative can lead to alloimmunization after transfusion or pregnancy. Molecular techniques have now been used to identify DEL variants. They are commonly encountered in the East Asian population with RHD(K409K) being the most frequent allele. RHD(M295I) is the most common DEL allele in Caucasians. As there is a paucity of data on DEL phenotype in the Indian population, the study aims to screen RhD negative individuals for two most common DEL mutations.

MATERIAL AND METHODS

EDTA blood was collected from 900 RhD negative individuals. Serological analysis included testing for the five major Rh antigens- C, c, D, E, and e by tube technique. Samples showing negative reaction for the presence of D antigen by Indirect Antiglobulin test were further tested for DEL phenotype by adsorption and elution technique. Molecular analysis involved DNA extraction and testing by PCR-SSP for RHD(K409K) and RHD(M295I) DEL alleles.

RESULTS

Rh phenotyping showed 153 Rh negative individuals with r'r, ten with r''r and 737 with rr phenotype. All the samples tested negative for RhD antigen by adsorption and elution method. The two common DEL mutations RHD(K409K) and RHD(M295I) were also not detected in the study population.

CONCLUSION

The study population showed the absence of the two common DEL alleles, concluding the variant to be rare. A comprehensive study with a larger sample size to look for other DEL mutations should be performed.

Anti-D Antibodies in Pregnant D Variant Antigen Carriers Initially Typed as RhD

BACKGROUND

To evaluate the incidence, the consequences, and the prevention strategy of anti-D alloimmunizations of D variant carriers in the obstetric population of Split-Dalmatia County, Croatia.

METHODS

RhD immunization events were evaluated retrospectively for the period between 1993 and 2012. Women were tested for RhD antigen and irregular antibodies. Those with anti-D antibody who were not serologically D- were genotyped for RHD. They were evaluated for their obstetric and transfusion history and their titer of anti-D. The neonates were evaluated for RhD status, direct antiglobulin test (DAT), hemoglobin and bilirubin levels, transfusion therapy as well as phototherapy and outcome.

RESULTS

Out of 104,884 live births 102,982 women were tested for RhD antigen. Anti-D immunization occurred in 184 women which accounts for 0.9% of individuals at risk of anti-D formation. 181 cases occurred in women serologically typed as D-. Three women were partial D carriers (DVa n = 2, DNB n = 1), initially typed RhD+, and recognized as D variant carriers after the immunization occurred. Anti-D titer varied from 1:1 to 1:16. Six children were RhD+, four had positive DAT, and two underwent phototherapy.

CONCLUSION

Anti-D immunization occurred in pregnant partial D carriers (DVa, DNB). RhD+ children had serologic markers of hemolytic disease of the fetus and newborn (HDFN), with no cases of severe HDFN.