RHD PCR of D-Negative Blood Donors

Weak D testing might be discontinued for RhD-negative blood donors with C and E negative phenotypes in the Indian population

BACKGROUND

Although serological testing to determine weak D status using the antihuman globulin reagent has been phased out for RhD-negative donors in many countries after the availability of RHD genotyping, it is routinely performed in India. However, weak D testing is a resource-intensive and time-consuming process. We devised a new algorithm for weak D testing in RhD-negative blood donors by performing CcEe phenotyping followed by weak D testing in only C+ and/or E + samples and compared it with the existing protocol in terms of time and cost-effectiveness.

METHOD

In this observational study, we tested 500 samples of RhD-negative blood donors over one year in India. The existing and new algorithms were compared, and the agreement was calculated in terms of the test results, time required for testing, and total cost involved. The RhD type, weak D status, and CcEe phenotypes were determined using the conventional tube technique. An adsorption-elution test was performed to check for the Del phenotype. We conducted RHD genotyping for all samples negative for weak D testing.

RESULTS

The proposed algorithm showed perfect agreement with the existing protocol (agreement = 100 %; κ= 1.00). By applying the new algorithm, we could reduce 71.63 % of testing time and 24 % of total cost without missing any weak D positive samples in blood donors.

CONCLUSIONS

Weak D testing might be discontinued for RhD-negative blood donors with C and E negative phenotypes in the Indian population and could be restricted to only C+ and/or E + phenotypes, which seems to be a time- and cost-effective testing strategy.

Genotype analysis to clarify RhD variants in discrepant samples of Chilean population

Introduction

The D antigen variants are classified as weak, partial, and extremely weak (DEL) and can be differentiated using molecular tests. In Chile, the laboratories of local blood centers do not identify variants of the D antigen, referring them for study to the Reference Laboratory of the Public Health Institute of Chile. So, our aim was to talk about the results of the molecular analysis of variants of the D antigen in samples that had different results in the serological classification.

Methods

In the D antigen classification of the Rh system, 479 samples with serological discrepant results were sent for molecular analysis. The Rh phenotype was performed with monoclonal anti-C, anti-c, anti-E, and anti-e antisera by direct agglutination. To find the D antigen, researchers used direct agglutination with monoclonal antisera and indirect antiglobulin testing with the column (gel) agglutination method. Molecular analysis was performed with a polymerase chain reaction with sequence-specific primers (SSP-PCR) and sequencing.

Results and discussion

The presence of D antigen variants was confirmed in 332 samples (69.3%), with an initial discrepancy in serological classification. In this group of discrepant samples, the frequency of weak RhD variants was 66% (219/332), that of extremely weak RhD was 28% (93/332), and that of partial RhD was 6% (20/332). The weak variants type 2 (27.4%), type 3 (8.4%), type 48 (8.4%), and type 1 (8.1%) were the next most prevalent variants after RHD*DEL43 (28%). The ccEe (R2r) phenotype was the most frequently detected (38.4%) and is present in 87% of the RHD*DEL43 samples. The E antigen is associated with the presence of this variant. Our analyses give the first description of D antigen variants in Chile. The most common variants are DEL type (RHD*DEL43) and weak (weak type 2), which are linked to the ccDEe (R2r) phenotype. These findings allow us to characterize the variants of the D antigen in Chile and, according to the obtained data, to design strategies for the management of donors, patients, and pregnant women.

DEL variants: review of molecular mechanisms, clinical consequences and molecular testing strategy

Patients with DEL phenotype, a D variant with a low number of D antigens per red blood cell, are routinely typed as RhD-negative in serology testing and are detectable only by adsorption and elution techniques or molecular methods. DEL is of clinical importance worldwide, as indicated by its genotype-phenotype discrepancies among different populations and its potential to cause anti-D alloimmunization when DEL phenotype individuals are inadvertently managed as RhD-negative. This narrative review summarized the DEL alleles causing DEL phenotype and the underlying mechanisms. The clinical consequences and current molecular testing approach were discussed to manage the transfusion needs of patients and donors with DEL phenotype.

Misclassification of RhD variants among pregnant women: a systematic review

The D antigen of the Rh blood group is considered clinically significant due to its ability to cause hemolytic transfusion reactions and hemolytic disease in the fetus and newborn. This systematic review discusses the prevalence of RhD variants among pregnant women and the importance of including RhD genotyping for prenatal testing to detect RhD variants and prevent anti-D alloimmunization. A comprehensive literature search was conducted using scientific search engines, including PubMed and MEDLINE databases, with the keywords 'anti-D alloimmunization', 'RhD variant', and 'pregnant women.' The review adhered to the PRISMA guidelines. Meta-analysis was performed using MedCalc version 20. A significance level of p≤0.05 was considered statistically significant for all two-tailed tests. The meta-analysis included four articles that met the inclusion criteria. The total prevalence of RhD positivity (RhD+) was 61% (95% CI:34%-85%). The prevalence ranged from 22% to 82%, indicating a high degree of heterogeneity between studies (I2=98.71%, p<0.0001). The overall prevalence of D variants was 15% (95% CI, 9%-23%) with a prevalence of 0.05% to 100%, showing a high degree of heterogeneity between studies (I2=99.89%, p<0.0001). Anti-D alloimmunization could occur in pregnant women with some types of RhD variants. All four studies focused on molecular testing of samples showing inconsistent or weak results with at least two anti-D antibodies using serological methods.

RhD alloimmunization by DEL variant missed in donor testing

INTRODUCTION

Exposure to normal or variably expressed RhD antigens in an antigen-negative individual can elicit an immune response and lead to the formation of clinically significant anti-D alloantibodies. We present the case of anti-D alloimmunization by DEL variant missed in routine blood donor screening.

MATERIAL AND METHODS

Blood donors were typed for D antigen using the direct serologic micromethod. Nonreactive samples were confirmed in the indirect antiglobulin method with an IgM/IgG anti-D monoclonal reagent. Genomic DNA was extracted using a commercial QIAamp DNA Blood Mini kit on the QIAcube device (Qiaqen, Germany). RHD genotyping was performed using the PCR-SSP genotyping kits- Ready Gene D weak, Ready Gene D weak screen, Ready Gene CDE, and Ready Gene D AddOn (Inno-Train, Germany). Unidentified alleles were sent for DNA genome sequencing.

RESULTS

After identifying DEL positive blood units in RhD negative blood donor pool, a look-back study was performed to determine if their previous donations caused alloimmunization in recipients. Out of 40 D negative recipients, one developed anti-D alloantibody after 45 days. The patient did not receive other RhD positive blood products. Blood donor typed D negative in direct and indirect agglutination method. RHD screening was positive, but RHD genotyping and DNA sequencing showed no mutation indicating the normal genotype.

CONCLUSION

Currently used methods in RHD genotyping are insufficient to identify many variant alleles, especially intronic variations. We suggest additional gene investigation including yet unexplored regions of regulation and intron regions to justify our serological finding.

DEL in China: the D antigen among serologic RhD-negative individuals

BACKGROUND

Providing RhD-negative red cell transfusions is a challenge in East Asia, represented by China, Korea, and Japan, where the frequency of RhD-negative is the lowest in the world.

FINDINGS

Among 56 ethnic groups in China, the RhD-negative frequency in Han, the prevalent ethnicity, is 0.5% or less, similar to most other ethnic groups. The Uyghur ethnic group has the highest reported RhD-negative frequency of up to 4.7%, as compared to 13.9% in the US. However, an estimated 7.15 million RhD-negative people live in China. The RhD-negative phenotype typically results from a loss of the entire RHD gene, causing the lack of the RhD protein and D antigen. The DEL phenotype carries a low amount of the D antigen and types as RhD-negative in routine serology. The DEL prevalence in RhD-negative individuals averages 23.3% in the Han, 17% in the Hui and 2.4% in the Uyghur ethnicities. The Asian type DEL, also known as RHD*DEL1 and RHD:c.1227G > A allele, is by far the most prevalent among the 13 DEL alleles observed in China.

CONCLUSION

The purpose of this review is to summarize the data on DEL and to provide a basis for practical strategy decisions in managing patients and donors with DEL alleles in East Asia using molecular assays.

Serological Detection of Rh-Del Phenotype among Rh-Negative Blood Donors at National Blood Center, Yangon, Myanmar

Background

Red cell Rhesus (Rh) antigen expression is influenced by the genetic polymorphism of RHD and RHCE genes and reveals serologically different reactions of RhD variants such as partial D, weak D, and Rh-Del. Serologically, Rh-Del type can only be detected by an adsorption-elution technique, and it might be mistyped as Rh-negative. The prevalence of Rh-Del has not been reported yet in Myanmar.

Method

A total of 222 Rh-negative blood donors in the National Blood Center were tested for weak D and Rh-Del by indirect antihuman globulin and adsorption-elution method, respectively. RhCE typing was performed among Rh-negative and Rh-Del.

Results

Of them, 75.2% (167/222) were Rh-negative, 15.8% (35/222) were Rh-Del, and 9% (20/222) were weak D. Of 202 blood donors (167 true Rh-negative and 35 Rh-Del), all of the Rh-Del positives were C-antigen-positive with 94.3% Ccee phenotype (33/35) and 5.7% CCee (2/35). Most of the Rh-negative donors (80.2%) were ccee phenotype (134/167).

Conclusion

About half of Rh-Del subjects were repeated donors, and attention was needed to avoid transfusion of truly Rh-negative patients to prevent alloimmunization. It is recommended to do Rh-Del typing of Rh-negative donors who are C-antigen-positive and consider moving them to the Rh-positive pool. Further study is needed to clarify the alloimmunization status for transfusion of Rh-Del blood to Rh-negative recipients. Molecular markers for RhD-negative and D variants should be established in the Myanmar population to improve selection of antisera for Rh typing and enhance safety of the transfusion services.

Characterization of RHD alleles present in serologically RHD-negative donors determined by a sensitive microplate technique

BACKGROUND AND OBJECTIVES

Weak D phenotypes with very low antigen densities and DEL phenotype may not be detected in RhD typing routine and could be typed as D-negative, leading to D alloimmunization of D-negative recipients. The present study aimed to investigate the presence of RHD-positive genotypes in blood donors typed as D-negative by an automated system using the solid-phase methodology as a confirmatory test.

METHODS

Two screenings were performed in different selected donor populations. For the first screening, we selected 1403 blood donor samples typed as D-negative regardless of the CE status, and in the second screening, we selected 517 donor samples typed as D-negative C+ and/or E+. RhD typing was performed by microplate in an automated equipment (Neo-Immucor®), and the confirmatory test was performed by solid-phase technique using Capture R® technology. A multiplex PCR specific to RHD and RHDψ was performed in a pool of 6 DNA samples. Sequencing of RHD exons was performed in all RHD-positive samples, and a specific PCR was used to identify the D-CE(4-7)-D hybrid gene.

RESULTS AND CONCLUSION

No weak D type was found in either screening populations. Additionally, 353 (18·4%) D-negative samples presented previously reported non-functional RHD genes, 2 samples had a DEL allele, and 6 samples demonstrated new alleles, including one novel DEL allele. Our study identified six new RHD alleles and showed that the inclusion of a confirmatory test using serological methodology with high sensitivity can reduce the frequency of weak D samples typed as D-negative.

Recommendations Regarding Practical DEL Typing Strategies for Serologically D-Negative Asian Donors

Background

DEL, the weakest D variant, is mistyped as D-negative by routine serological assays. Transfusion of red blood cells expressing the DEL phenotype has the potential to elicit anti-D alloimmunization in D-negative recipients. The goal of this study was to recommend DEL typing strategies for serologically D-negative Asian donors.

Methods

RhCE phenotyping and the adsorption-elution test were performed on 674 serologically D-negative samples. RHD genotyping using real-time polymerase chain reaction and melting curve analysis were also undertaken to identify DEL alleles. Costs and turnaround time of RhCE phenotyping, the adsorption-elution test, and RHD genotyping were estimated.

Results

Sensitivity and specificity of the adsorption-elution test for serologically D-negative samples were 94.9% (93/98) and 91.5% (527/576), respectively. C+ phenotypes were detected in all 98 samples with DEL alleles. Despite comparable costs, RHD genotyping was more accurate and rapid than the adsorption-elution test.

Conclusions

Two practical DEL typing strategies using RhCE phenotyping as an initial screening method were recommended for serologically D-negative Asian donors. Compared with DEL typing using RHD genotyping, serological DEL typing using adsorption-elution test is predicted to increase the incidence of anti-D alloimmunization and decrease the D-negative donor pool without having any cost-competitiveness but can be used in laboratories where molecular methods are not applicable.

Development and evaluation of a transfusion medicine genome wide genotyping array

BACKGROUND

Many aspects of transfusion medicine are affected by genetics. Current single-nucleotide polymorphism (SNP) arrays are limited in the number of targets that can be interrogated and cannot detect all variation of interest. We designed a transfusion medicine array (TM-Array) for study of both common and rare transfusion-relevant variations in genetically diverse donor and recipient populations.

STUDY DESIGN AND METHODS

The array was designed by conducting extensive bioinformatics mining and consulting experts to identify genes and genetic variation related to a wide range of transfusion medicine clinical relevant and research-related topics. Copy number polymorphisms were added in the alpha globin, beta globin, and Rh gene clusters.

RESULTS

The final array contains approximately 879,000 SNP and copy number polymorphism markers. Over 99% of SNPs were called reliably. Technical replication showed the array to be robust and reproducible, with an error rate less than 0.03%. The array also had a very low Mendelian error rate (average parent-child trio accuracy of 0.9997). Blood group results were in concordance with serology testing results, and the array accurately identifies rare variants (minor allele frequency of 0.5%). The array achieved high genome-wide imputation coverage for African-American (97.5%), Hispanic (96.1%), East Asian (94.6%), and white (96.1%) genomes at a minor allele frequency of 5%.

CONCLUSIONS

A custom array for transfusion medicine research has been designed and evaluated. It gives wide coverage and accurate identification of rare SNPs in diverse populations. The TM-Array will be useful for future genetic studies in the diverse fields of transfusion medicine research.

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.

DEL phenotype

DEL red blood cells (RBCs) type as D- by routine serologic methods and are transfused routinely, without being identified as expressing a very weak D antigen, to D- recipients. DEL RBCs are detected only by adsorption and elution of anti-D or by molecular methods. Most DEL phenotypes have been reported in population studies conducted in East Asia, although DEL phenotypes have been detected also among Caucasian individuals. Approximately 98 percent of DEL phenotypes in East Asians are associated with the RHD*DEL1 or RHD*01EL.01 allele. The prevalence of DEL phenotypes has been reported among D- Han Chinese (30%), Japanese (28%), and Korean (17%) populations. The prevalence of DEL phenotypes is significantly lower among D- Caucasian populations (0.1%). Among the 3-5 percent of African individuals who are D-, there are no reports of the DEL phenotype. Case reports from East Asia indicate that transfusion of DEL RBCs to D- recipients has been associated with D alloimmunization. East Asian immigrants constitute 2.1 percent of the 318.9 million persons residing in the United States, and an estimated 2.8 percent are blood donors. Using these statistics, we estimate that 68-683 units of DEL RBCs from donors of East Asian ancestry are transfused as D- annually in the United States. Given the reports from East Asia of D alloimmunization attributed to transfusion of DEL RBCs, one would expect an occasional report of D alloimmunization in the United States following transfusion of DEL RBCs to a D- recipient. If such cases do occur, the most likely reason that they are not detected is the absence of active post-transfusion monitoring for formation of anti-D.

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.

Clinical and laboratory update on the DEL variant

Serological assays for the RhD blood group are based on detection of the RhD antigen on human red blood cells using a specific anti-D antibody. The weak expression of the RhD antigen in the DEL variant hinders the sensitivity of conventional serological assays. Evidence of anti-D immunization in patients with D-negativity who have received DEL-variant blood units has been reported in various populations. This observation has prompted the need for genetic epidemiological and clinical data on the DEL variant in the development of DEL molecular diagnostic testing. This review highlights the molecular features of the DEL variant, the clinical consequences of DEL-blood transfusion, and current approaches for detection of the DEL-variant for donor screening and transfusion.

Rhesus Negative Woman Transfused With Rhesus Positive Blood: Subsequent Normal Pregnancy Without Anti D production

Clinicians sometimes are confronted with the challenge of transfusing haemorrhaging Rhesus (Rh) D negative patients with Rh D positive blood to save their lives. There are concerns about alloimmunization and future haemolytic disease of the newborn in women of the reproductive age. Another fear is transfusion reaction if they receive another Rh D positive blood in future. We present a 32-year-old Rh D negative woman, who had postpartum haemorrhage in her first pregnancy and was transfused with Rh D positive blood because of unavailability of Rh D negative blood. She did not receive anti D immunoglobin but subsequently had a normal term pregnancy of an Rh positive fetus without any detectable anti D antibodies throughout the pregnancy. In life threatening situations from obstetric haemorrhage, transfusion of Rh D negative women with Rh D positive blood should be considered as the last resort.

Dried blood spots of pooled samples for RHD gene screening in blood donors of mixed ancestry

OBJECTIVES

In this study, we present a strategy for RHD gene screening based on real-time polymerase chain reaction (PCR) using dried blood spots of pooled samples.

BACKGROUND

Molecular analysis of blood donors may be used to detect RHD variants among the presumed D-negative individuals. RHD genotyping using pooled samples is a strategy to test a large number of samples at a more reasonable cost.

MATERIALS AND METHODS

RHD gene detection based on real-time PCR using dried blood spots of pooled samples was standardised and used to evaluate 1550 Brazilian blood donors phenotyped as RhD-negative. Positive results were re-evaluated by retesting single samples using real-time PCR and conventional multiplex PCR to amplify five RHD-specific exons. PCR-sequence-specific primers was used to amplify RHDψ allele.

RESULTS

We devised a strategy for RHD gene screening using dried blood spots of five pooled samples. Among 1550 serologically D-negative blood donors, 58 (3.74%) had the RHD gene. The non-functional RHDψ allele was detected in 47 samples (3.02%).

CONCLUSION

The present method is a promising strategy to detect the RHD gene among presumed RhD-negative blood donors, particularly for populations with African ancestry.

The RHD(1227G>A) DEL-associated allele is the most prevalent DEL allele in Australian D- blood donors with C+ and/or E+ phenotypes

BACKGROUND

Red blood cells (RBCs) with D antigen levels only detected by anti-D adsorption-elution and an antiglobulin test express a DEL phenotype. For two DEL types, including RHD(1227G>A), immunization of D- recipients has been reported. This study's aim was to measure the prevalence of DEL-associated RHD alleles in a cohort of Australian D- donors to develop a model to estimate alloimmunization risk.

STUDY DESIGN AND METHODS

D-, C+ and/or E+ blood donors were screened for RHD exons using quantitative polymerase chain reaction. Donors with RHD signals were DEL phenotyped with MCAD6 anti-D. RHD alleles were characterized via single-nucleotide polymorphism array or sequencing. Extended DEL phenotyping was performed with an anti-D panel.

RESULTS

Among 2027 donors, 39 carried RHD alleles that have been previously reported to associate with either the DEL or the weak D phenotype. An additional five donors carried previously unreported RHD alleles and exhibited the DEL phenotype: RHD(IVS2-2delA), RHD(IVS1+5G>C), RHD(ex9:del/CE), and RHD(ex8:del/CE) represented twice. In total, DEL/weak D-associated RHD alleles were detected in 44 of 2027 donors or 2.17% (95% confidence interval, 1.54%-2.81%). The RHD(1227G>A) DEL allele was the most frequent (n = 16). The risk of transfusing D- females not more than 40 years of age with an RHD(1227G>A) DEL RBC unit (when managed as D-) is estimated to be one in 149,109 transfusions (range, 100,680-294,490).

CONCLUSION

DEL/weak D-associated RHD alleles were found in 2.17% of Australian D-, C+ and/or E+ blood donors. This differs from previous European reports in that the clinically significant RHD(1227G>A) DEL allele is the most prevalent.

Implementation of a mandatory donor RHD screening in Switzerland

Starting in 2013, blood donors must be tested at least using: (1) one monoclonal anti-D and one anti-CDE (alternatively full RhCcEe phenotyping), and (2) all RhD negative donors must be tested for RHD exons 5 and 10 plus one further exonic, or intronic RHD specificity, according to the guidelines of the Blood Transfusion Service of the Swiss Red Cross (BTS SRC). In 2012 an adequate stock of RHD screened donors was built. Of all 25,370 RhD negative Swiss donors tested in 2012, 20,015 tested at BTS Berne and 5355 at BTS Zürich, showed 120 (0.47%) RHD positivity. Thirty-seven (0.15%) had to be redefined as RhD positive. Routine molecular RHD screening is reliable, rapid and cost-effective and provides safer RBC units in Switzerland.