How I manage donors and patients with a weak D phenotype

Evaluation of the LightCycler® PRO Instrument as a Platform for Rhesus D Typing

Rapid and reliable Rhesus D typing is crucial for blood donation centers. In instances of massive blood transfusion or reduced antigen expression, DNA-based phenotype prediction becomes mandatory. Our molecular RHD typing approach involves an initial real-time PCR for the most common aberrant RHD types in our region, RHD*01W.1 (weak D type 1), RHD*01W.2 (weak D type 2), RHD*01W.3 (weak D type 3), and RHD*07.01 (DVII). For comprehensive coverage, Sanger sequencing of RHD coding regions is performed in the case of PCR target-negative results. We evaluated the specificity and accuracy of these methods using the recently launched LightCycler® PRO real-time platform. All findings demonstrated remarkable accuracy. Notably, the LightCycler® PRO instrument offers a distinct advantage in data interpretation and integration via the HL7 interface. This study underlines the importance of including advanced molecular techniques in blood typing protocols, especially in scenarios where conventional serological methods may be insufficient.

A Bioinformatically Initiated Approach to Evaluate GATA1 Regulatory Regions in Samples with Weak D, Del, or D- Phenotypes Despite Normal RHD Exons

Introduction

With over 360 blood group antigens in systems recognized, there are antigens, such as RhD, which demonstrate a quantitative reduction in antigen expression due to nucleotide variants in the non-coding region of the gene that result in aberrant splicing or a regulatory mechanism. This study aimed to evaluate bioinformatically predicted GATA1-binding regulatory motifs in the RHD gene for samples presenting with weak or apparently negative RhD antigen expression but showing normal RHD exons.

Methods

Publicly available open chromatin region data were overlayed with GATA1 motif candidates in RHD. Genomic DNA from weak D, Del or D- samples with normal RHD exons (n = 13) was used to confirm RHD zygosity by quantitative PCR. Then, RHD promoter, intron 1, and intron 2 regions were amplified for Sanger sequencing to detect potential disruptions in the GATA1 motif candidates. Electrophoretic mobility shift assay (EMSA) was performed to assess GATA1-binding. Luciferase assays were used to assess transcriptional activity.

Results

Bioinformatic analysis identified five of six GATA1 motif candidates in the promoter, intron 1 and intron 2 for investigation in the samples. Luciferase assays showed an enhancement in transcription for GATA1 motifs in intron 1 and for intron 2 only when the R 2 haplotype variant (rs675072G>A) was present. GATA1 motifs were intact in 12 of 13 samples. For one sample with a Del phenotype, a novel RHD c.1-110A>C variant disrupted the GATA1 motif in the promoter which was supported by a lack of a GATA1 supershift in the EMSA and 73% transcriptional activity in the luciferase assay. Two samples were D+/D- chimeras.

Conclusion

The bioinformatic predictions enabled the identification of a novel DEL allele, RHD c.1-110A>C, which disrupted the GATA1 motif in the proximal promoter. Although the majority of the samples investigated here remain unexplained, we provide GATA1 targets which may benefit future RHD regulatory investigations.

40 years of researching the Del phenotype results in a change of transfusion practice

Anti-D cannot agglutinate red cells of any Del phenotype in routine serology. Many individuals with East Asian ancestry who type D-negative in serology harbor a Del phenotype. Almost all such individuals carry one distinct DEL variant, dubbed Asian-type DEL, known as RHD*01EL.01, RHD*DEL1, RHD:c.1227G>A, formerly known as RHD(K409K). Clinical evidence strongly suggests that Asian-type DEL individuals can safely be transfused with RhD-positive blood and do not need anti-D prophylaxis in pregnancy.

Fetal RHD Screening in RH1 Negative Pregnant Women: Experience in Switzerland

RH1 incompatibility between mother and fetus can cause hemolytic disease of the fetus and newborn. In Switzerland, fetal RHD genotyping from maternal blood has been recommended from gestational age 18 onwards since the year 2020. This facilitates tailored administration of RH immunoglobulin (RHIG) only to RH1 negative women carrying a RH1 positive fetus. Data from 30 months of noninvasive fetal RHD screening is presented. Cell-free DNA was extracted from 7192 plasma samples using a commercial kit, followed by an in-house qPCR to detect RHD exons 5 and 7, in addition to an amplification control. Valid results were obtained from 7072 samples, with 4515 (64%) fetuses typed RHD positive and 2556 (36%) fetuses being RHD negative. A total of 120 samples led to inconclusive results due to the presence of maternal or fetal RHD variants (46%), followed by women being serologically RH1 positive (37%), and technical issues (17%). One sample was typed false positive, possibly due to contamination. No false negative results were observed. We show that unnecessary administration of RHIG can be avoided for more than one third of RH1 negative pregnant women in Switzerland. This reduces the risks of exposure to a blood-derived product and conserves this limited resource to women in actual need.

Molecular and serological analysis of the D variant in the Chinese population and identification of seven novel RHD alleles

BACKGROUND

The molecular basis of the D variant phenotype in the Chinese differs greatly from that of the Caucasian. Adapting a specific D typing strategy to the spectrum of prevalent RHD variant alleles is necessary.

STUDY DESIGN AND METHODS

Blood samples with ambiguous D phenotypes were collected in the Southern Chinese population. A special three-step typing strategy was applied. First, the common DVI type 3 was identified from epitope profiles of D antigen. Then, another common weak D type 15 (RHD*845A) was identified by epitope profiles of D antigen and Sanger sequencing of RHD exon 6. Finally, the remaining D variants were genotyped mainly by Sanger sequencing. For the novel RHD alleles in the coding region and exon-intron junction, in vitro transfection and minigene splicing assays were performed, respectively. The anti-D investigation was performed.

RESULTS

DVI type 3 (65/253, 25.7%) and weak D type 15 (62/253, 24.5%) were common Chinese D variants, and RHD*960A, DFR, RHD*weak D type 25, 72, and 136 were frequent variant RHD alleles. Besides, twenty-two sporadic and seven novel RHD alleles (RHD*188A; RHD*688C; RHD*782 T; RHD*1181C; RHD*165 T, 993A; RHD*148 + 3G > T and RHD*1227 + 5G > C) were identified. The deleterious effect of the novel RHD alleles on D antigen or mRNA expression was confirmed. Anti-D was detected in two DVI type 3 pregnant women.

DISCUSSION

The three-step typing strategy provides an effective approach for Chinese D variant typing. It can be anticipated that commercially available RHD genotyping kits have limitations for testing Chinese D variants, as some of the frequent variants are not interrogated.

Transfusion management of Africans with RHD variants in China

The presence of D variant among minorities could produce a higher rate of alloimmunization observed in patients from this group. This is partly due to the ethnic and racial specificity of RHD variants and the limited availability of Rh-matched blood donors. Approximately half a million African migrants in China carrying distinct Rh blood type composition have presented to the health care system with an imperative safety requirement of blood transfusion among 1.3 billion Chinese individuals. We depict the clinically significant RHD alleles among African migrants living in China and identify the genetic similarities and disparities to Chinese. We discussed practical strategies to manage the unique transfusion needs of African migrants in China.

Weak D type 42: Antigen density and risk of alloimmunization in the province of Québec

BACKGROUND AND OBJECTIVES

A high proportion of suspected weak D patients referred to Héma-Québec were genotyped as weak D type 42 (368/2105, 17.5%). These patients are currently considered D with regard to RhD immunoprophylaxis in pregnancy and transfusion. The goal of this study was to retrospectively evaluate the risk of alloimmunization in weak D type 42 patients and to characterize their RhD surface molecule expression on red blood cells (RBCs) in comparison to other weak D types (1, 2 and 3).

MATERIALS AND METHODS

A retrospective analysis using the weak D type 42 patients' medical data to verify potential anti-D alloimmunization events was conducted. Quantitative analyses using flow cytometry were also performed on RBCs to quantify the cell surface density of the D antigen.

RESULTS

Data on 215 subjects with weak D type 42 were reviewed. None developed immune allo-anti-D; three had definite exposure to D+ red cells and 41 had possible exposure through pregnancy. Flow cytometry analysis showed that weak D types 1, 2, 3 and 42 had relative antigen densities of 2.7%, 2.2%, 8.1% and 3.6%, respectively, with R1R2 red cells referencing 100% density. The estimated antigen density range of weak D type 42 was 819-1104 sites per RBC.

CONCLUSION

Our retrospective alloimmunization data analysis and antigen density study establish a basis for the consideration of a weak D type 42 individual as D+. This consideration would allow for a targeted reduction of RhD immunoprophylaxis in pregnancy and the unjustified use of D- units for transfusion.

Blood Group Testing

Red blood cell (RBC) transfusion is one of the most frequently performed clinical procedures and therapies to improve tissue oxygen delivery in hospitalized patients worldwide. Generally, the cross-match is the mandatory test in place to meet the clinical needs of RBC transfusion by examining donor-recipient compatibility with antigens and antibodies of blood groups. Blood groups are usually an individual's combination of antigens on the surface of RBCs, typically of the ABO blood group system and the RH blood group system. Accurate and reliable blood group typing is critical before blood transfusion. Serological testing is the routine method for blood group typing based on hemagglutination reactions with RBC antigens against specific antibodies. Nevertheless, emerging technologies for blood group testing may be alternative and supplemental approaches when serological methods cannot determine blood groups. Moreover, some new technologies, such as the evolving applications of blood group genotyping, can precisely identify variant antigens for clinical significance. Therefore, this review mainly presents a clinical overview and perspective of emerging technologies in blood group testing based on the literature. Collectively, this may highlight the most promising strategies and promote blood group typing development to ensure blood transfusion safety.

Updated Evaluation of RhD Status Among Women of Child-Bearing Age in Detroit, Michigan

OBJECTIVES

The Rh blood group system is one of the most important and immunogenic blood group systems after the ABO blood group system and, like other blood group antigens, it follows ethnic and racial trends. However, when it comes to D variants-partial D and weak D-most of the cohorts studied in the literature have been of European descent. This study aimed to discover the variant D trends in Detroit, Michigan, with an emphasis on Black communities.

METHODS

From 2016 to 2018, there were 102 patients (women of childbearing potential: < 50 years) at Henry Ford Hospital that had serologic D discrepant testing. These patients were sent out for molecular RHD determination.

RESULTS

In total, 12.7% of patients were characterized as RhD positive and 87.3% of patients were characterized as RhD variants (nominated as RhD negative at our institution).

CONCLUSIONS

Our predominantly Black cohort sheds light on the diversity of the RhD antigen. The majority of Blacks were classified as RhD variants (RhD negative nomination at our institution). Therefore, molecular testing for this patient population with serologic RhD discrepancies is paramount to properly manage their obstetric care.

High prevalence of weak D type 42 in a large-scale RHD genotyping program in the province of Quebec (Canada)

BACKGROUND

The determination of the RhD phenotype is crucial to avoid alloimmunization, especially in childbearing women. Following the 2015 recommendation from the Work Group on RHD Genotyping, a large-scale RHD genotyping program was implemented in the province of Quebec (Canada) and offered to women ≤45 years old with a serological weak D or discordant results. Since weak D type 42 was previously shown to be prevalent among French Canadians, genotyping for that variant was also performed. Our aim was to report the prevalence of the weak D alleles in the province of Quebec.

STUDY DESIGN AND METHODS

A retrospective study of 2105 women with serological weak D referred to Hema-Quebec's immunohematology reference laboratory (IRL) between June 2016 and May 2020 was conducted. Results from the serological tests performed by the referring hospital were compiled and RHD were genotyped.

RESULTS

Most patients presented at least one serological result ≤2+ before being referred to Hema-Quebec. Weak D type 42 was the most prevalent variant, representing 17.5% (368/2105) of all individuals tested. Only 15.3% (323/2105) of patients were weak D type 1, 3.3% (69/2105) were type 2, and 8.6% (180/2105) were type 3. Weak D type 42 is highly expressed in regions with low immigration rate and known for their founder effect.

CONCLUSION

Our RHD genotyping program allowed for a better management of weak D. The province of Quebec presents a unique RHD genotype distribution. We confirmed that weak D type 42 is associated with a founder effect found in Caucasian French Canadians.

Molecular Characteristics of the Serological Weak D Phenotype in Koreans

Serological weak D is a reaction of 2+ or less to anti-D reagent and includes weak D and partial D phenotypes. Although identifying the RhD subtype is important for transfusion safety, serological tests are insufficient for defining the RhD subtype, and molecular tests are needed. To analyze the molecular characteristics of D variants in Koreans to facilitate the formulation of individualized transfusion strategies, molecular tests such as RhD genotyping using real-time polymerase chain reaction (PCR) and partial-D and/or weak-D sequence-specific amplification (SSP) were performed on 105 Korean Rare Blood Program (KRBP) patients exhibiting serological weak D. In total, 58 out of 68 serologically determined weak D KRBP patients were typed as having weak D or partial D phenotypes via RhD genotyping. In detail, eight (13.8%) were typed as partial DVa or DBS, nine (15.5%) as weak D type 15, and four others (6.8%) as partial DVI, partial DVII, weak D type 2, or weak D type 41 or 45, whereas the rest (n = 37, 63.8%) was typed as having either weak D or partial D. This suggests that serological weak D Koreans who require transfusion should be treated as D-negative.

Transfusion support during childbirth for a woman with anti-U and the RHD*weak D type 4.0 allele

D- red blood cells (RBCs), always in short supply, and Rh immune globulin (RhIG) are not needed for patient care if D+ RBCs can safely be transfused. According to a recent work group recommendation, patients with the RHD*weak D type 4.0 allele can be considered D+. We report an African American woman who presented for delivery at the end of the third trimester, at which time anti-U and a serologic weak D phenotype were recognized, requiring U-, D- RBC units. We obtained 3 U- RBC units, including 1 D- unit. Later, the RHD*weak D type 4.0 allele was determined by RHD genotyping, only 6 days before delivery. The patient had an uneventful vaginal delivery of a D+ baby. No transfusion was needed for mother or baby. In this case, a pregnant woman with the RHD*weak D type 4.0 allele can safely be managed as D+, relaxing the unnecessary D- restriction for the limited U- RBC supply. The procured U-, D- RBC unit was frozen with 14 days of shelf-life remaining. To conserve D- RBC units, not limited to U-, for patients with a definite need, we recommend molecular analysis of a serologic weak D phenotype before a transfusion becomes imminent. The best time to resolve a serologic weak D phenotype with RHD genotyping is early in a pregnancy. Immunohematology 2021;37:1-4 .

D– red blood cells (RBCs), always in short supply, and Rh immune globulin (RhIG) are not needed for patient care if D+ RBCs can safely be transfused. According to a recent work group recommendation, patients with the RHD*weak D type 4.0 allele can be considered D+. We report an African American woman who presented for delivery at the end of the third trimester, at which time anti-U and a serologic weak D phenotype were recognized, requiring U–, D– RBC units. We obtained 3 U– RBC units, including 1 D– unit. Later, the RHD*weak D type 4.0 allele was determined by RHD genotyping, only 6 days before delivery. The patient had an uneventful vaginal delivery of a D+ baby. No transfusion was needed for mother or baby. In this case, a pregnant woman with the RHD*weak D type 4.0 allele can safely be managed as D+, relaxing the unnecessary D– restriction for the limited U– RBC supply. The procured U–, D– RBC unit was frozen with 14 days of shelf-life remaining. To conserve D– RBC units, not limited to U–, for patients with a definite need, we recommend molecular analysis of a serologic weak D phenotype before a transfusion becomes imminent. The best time to resolve a serologic weak D phenotype with RHD genotyping is early in a pregnancy. Immunohematology 2021;37:1–4 .

Insights into anti-D formation in carriers of RhD variants through studies of 3D intraprotein interactions

BACKGROUND

Many RhD variants associated with anti-D formation (partial D) in carriers exposed to the conventional D antigen carry mutations affecting extracellular loop residues. Surprisingly, some carry mutations affecting transmembrane or intracellular domains, positions not thought likely to have a major impact on D epitopes.

STUDY DESIGN AND METHODS

A wild-type Rh trimer (RhD₁ RhAG₂ ) was modeled by comparative modeling with the human RhCG structure. Taking trimer conformation, residue accessibility, and position relative to the lipid bilayer into account, we redefine the domains of the RhD protein. We generated models for RhD variants carrying one or two amino acid substitutions associated with anti-D formation in published articles (25 variants) or abstracts (12 variants) and for RHD*weak D type 38. We determined the extracellular substitutions and compared the interactions of the variants with those of the standard RhD.

RESULTS

The findings of the three-dimensional (3D) analysis were correlated with anti-D formation for 76% of RhD variants: 15 substitutions associated with anti-D formation concerned extracellular residues, and structural differences in intraprotein interactions relative to standard RhD were observed in the others. We discuss the mechanisms by which D epitopes may be modified in variants in which the extracellular residues are identical to those of standard RhD and provide arguments for the benignity of p.T379M (RHD*DAU0) and p.G278D (RHD*weak D type 38) in transfusion medicine.

CONCLUSION

The study of RhD intraprotein interactions and the precise redefinition of residue accessibility provide insight into the mechanisms through which RhD point mutations may lead to anti-D formation in carriers.

Impact of RHD genotyping on transfusion practice in Denmark and the United States and identification of novel RHD alleles

BACKGROUND

Reduced D antigen on red blood cells (RBCs) may be due to "partial" D phenotypes associated with loss of epitope(s) and risk for alloimmunization or "weak" D phenotypes that do not lack major epitopes with absence of clinical complications. Genotyping of samples with weak and discrepant D typing is recommended to guide transfusion and RhIG prophylaxis. The goal was to compare the impact of RHD genotyping on transfusion practice in two centers serving different populations.

STUDY DESIGN AND METHODS

Fifty-seven samples from Denmark and 353 from the United States with weak or discrepant D typing were genotyped. RBC typing was by multiple methods and reagents. DNA isolated from white blood cells was tested with RBC-Ready Gene D weak or CDE in Denmark or RHD BeadChip in the United States. RHD was sequenced for those unresolved.

RESULTS

Of Caucasian samples from Denmark, 90% (n = 51) had weak D types 1, 2, or 3; two had other weak D, two partial D, and two new alleles. In diverse ethnic U.S. samples, 44% (n = 155) had weak D types 1, 2, or 3 and 56% (n = 198) had other alleles: uncommon weak D (n = 13), weak 4.0 (n = 62), partial D (n = 107), no RHD (n = 9), and new alleles (n = 7).

CONCLUSION

Most samples with weak or variable D typing from Denmark had alleles without risk for anti-D. In U.S. samples, 48% could safely be treated as D+, 18% may require consideration if pregnancy possible, and 34% could potentially benefit from being treated as D-. Black and multiracial ethnicities were overrepresented relative to population.

RHD genotyping of serological weak D phenotypes in the Iranian blood donors and patients

BACKGROUND

Most prevalent weak D types in the Caucasians molecularly defined weak D types 1, 2 or 3 and can be managed safely as RhD-positive, conserving limited supplies of RhD-negative RBCs. Therefore, identification of RHD alleles prevalence in each population could improve the policies related to accuracy of RhD typing. The aim of this study was to determine the frequency of RHD variant alleles among donors and patients for the first time in Iran.

MATERIALS AND METHODS

RHD genotyping was performed on 100 blood donor and patient samples with weak D phenotype. PCR-SSP and DNA sequencing were used to identify the RHD alleles.

RESULTS

Molecular analysis showed only 15 samples were RHD*weak D 1(n = 13) and RHD*weak D 3(n = 2), and no cases of RHD*weak D 2 were detected. RHD*weak 15 (n = 43) was determined as the most prevalent D variants in our population and the other weak D types follows: RHD*weak 4, 5, 80 and one case of each one: RHD*weak 8, 11, 14, 100 and 105. Partial D variants also was identified in 18 samples as follows: RHD*partial DLO, DBT1, DV2, DHK and DAU-1.

CONCLUSION

The results of this study highlight the specific pattern of RHD status in the Iranian population. The weak D types 15 was the most common weak D type in the Iranian population. However, the screening for weak D types 1, 2 and 3 with 15 % frequency is also necessary for accurate RhD typing and developing clinical strategy of blood transfusion in weak D patients.

RHD and RHCE molecular analysis in weak D blood donors and in patients with Rh antibodies against their own corresponding Rh antigen

BACKGROUND

The Rh system is the largest and most polymorphic blood group system. The existence of a large number of RH alleles results in variant phenotypes that often complicate blood donor phenotyping and the distinction between auto- and allo-antibodies in recipients who have anti-Rh antibodies in the presence of their own corresponding Rh antigen. Knowledge of these variants is necessary in order to make blood transfusion safer.

MATERIALS AND METHODS

Samples from 48 blood donors with serological weak D and from 29 patients who had anti-Rh antibody in the presence of their own corresponding Rh antigen were evaluated molecularly for RHD and RHCE alleles using a blood-multiplex ligation-dependent probe amplification assay and Sanger sequencing.

RESULTS

Rh variants were found in 45 of the 48 blood donors: 24/45 (53%) were weak D, 2/45 (4%) partial D and 19/45 (42%) were weak and partial D. The remaining three donors (6%) did not show a mutation in the RHD allele. Among the 29 patients, 13/29 had anti-e, of whom 4/13 had genotypes that predicted a partial e antigen; 11/29 had anti-D, with 6/11 being identified as partial D; 2/29 had anti-c, of whom 1/2 was predicted to express partial c antigen; 4/29 who had anti-E and 4/29 who had anti-C did not show mutations in RHCE*C or RHCE*E.

DISCUSSION

It was possible to find individuals with clinically significant Rh phenotypes due to the weak reactivity of the D antigen, detected through serological tests in blood donors. In patients, when found with the anti-Rh antibody in the presence of the same Rh antigen, it is difficult to distinguish an auto-antibody from an allo-antibody by serological tests; in these cases, molecular methods (genotyping) can help us to determine whether there are changes in the RH alleles and to discover the nature of the antibody (allo or auto).

Molecular characterisation of RhD variants in North Indian blood donor population

OBJECTIVES

A molecular analysis of serologically RhD variant samples was conducted to find the incidence of various D variants in our blood donor population.

BACKGROUND

Determining a blood donor's RhD phenotype and genotype is important as transfusion of units with a weak D or partial D phenotype can result in immunisation of the recipients.

METHODS

Samples with discrepant D and weak D phenotypes identified on testing with at least five different monoclonal anti-D antisera were considered serological RhD variant and subjected to molecular testing (Massarray kit, Agena Bioscience, San Diego) for variant RHD gene.

RESULTS

A total of 39 samples, including 19 RhD discrepant samples and 20 weak D samples, were identified as serological RhD variant from a total of 4386 samples. Thirteen (13/39) samples carried variants leading to weak D phenotype, and eight samples had variants leading to partial D categories. Seven samples (7) could not be characterised, whereas 11 samples were identified as Rh negative (RHD*01N.01) after molecular testing. Overall incidence of D variants in the study population was 0.48%. RHD*weak D type 1(5, 0.1%) and RHD*DFR1 (5, 1%) were the most common variants identified.

CONCLUSIONS

Few samples with weak reaction on serological testing were found to be partial D variant and vice versa. Donor centres should develop a protocol for genotyping of samples with aberrant results on serological testing for assessing the actual RhD status of an individual as results of serological testing may be misleading.

A multi-centre study on the performance of the molecular genotyping platform ID RHD XT for resolving serological weak RhD phenotype in routine clinical practice

BACKGROUND AND OBJECTIVES

There is concern regarding the lack of prevention of unnecessary transfusion of RhD negative red cells and unnecessary administration of Rh immunoglobulin (RhIG) to pregnant women. In this study, performance of ID RHD XT, a genotyping assay for identification of six RHD allelic variants and human platelet antigens HPA-1a/1b was assessed.

MATERIALS AND METHODS

Whole blood samples presenting weak, discrepant or inconclusive D phenotype results were genotyped with ID RHD XT and compared to reference molecular tests. Candidacy for RhIG prophylaxis was determined by analysing samples from pregnant women. Hands-on time to complete the procedures was measured.

RESULTS

Overall, 167 samples were tested (55 donors, 56 patients, 52 pregnant women and four newborns). Agreement between ID RHD XT and the reference method was 100% (51% weak D type 1, 2 or 3; 35·5% weak D Types 1, 2 or 3 not detected; 4% RHD deletion; 1% RHD*Pseudogene; 1% RHD*DIIIa-CE(3-7)-D; and 4% no amplification variant detected for RHD genotype; and 64% HPA-1a/a; 30% HPA-1a/b; and 3% HPA-1b/b for HPA-1 genotype). Call rate was 98·2%. ID RHD XT identified 40% of the pregnant women that would not have required RhIG prophylaxis. Overall hands-on time was 25-45 min to process a batch of 24 samples, and four hours for total assay time.

CONCLUSION

ID RHD XT yielded reproducible results for RHD typing in serologically weak D phenotype individuals. ID RHD XT was proven useful for the correct management of patients with RhD serological discrepancies and the rational use of RhIG in pregnancy.

Evaluation of molecular typing and serological methods in solving discrepant results of weak and partial D (Rh) in South Egypt

INTRODUCTION

Rh discrepancies produced by partial and weak D phenotypes are a problem during routine testing. Some blood units with weak and partial D expression may be missed by serology. Overcoming the limitations of serology can be achieved by molecular typing. Our objective was to evaluate currently used serologic methods with the molecular analysis in solving discrepant results of weak and partial D (Rh) in South Egypt.

PATIENTS AND METHODS

Fifty blood donor and patient samples with undetermined D phenotype were subjected to serology to define their phenotype using identification (ID)-Card "ID-partial RhD typing set" using six monoclonal anti-D panels, followed by molecular typing using polymerase chain reaction sequence-specific primer kit.

RESULTS

Molecular typing confirmed most of the serology results; two samples previously resolved as partial D Type 3 and DFR by serological methods were clarified by molecular techniques - one sample as weak Type 4 and the other sample as weak Type 3. Among the weak D alleles found in our study, Type 4 was the most common, with a frequency of 20%, followed by Type 3 (14%), Type 1 (8%), Type 2 (6%), and finally, Type 5 with a frequency of 3%. The most common types of partial D were partial D Type D5 (14%) and Type D3 (10%).

CONCLUSION

Our study identified D variants (weak D and partial D categories) of the antigen D and determined the frequency and composition of partial D and weak D alleles in our population. Molecular typing also confirmed most of the results obtained from serological methods.

Strategies to identify candidates for D variant genotyping

BACKGROUND

RhD variants have altered D epitopes and/or decreased antigen copies per red cell. Individuals carrying these variants may test antigen negative, weakly positive, or positive by serology, and may or may not be at risk of alloimmunisation after exposure. There have been recommendations to perform RHD genotyping of patients, pregnant women and females of childbearing potential with serological weak D phenotype, to guide prophylactic use of Rh immune globulin (RhIG), and better conserve D-negative blood products. The purpose of this study was to evaluate the performance of a set of empirical criteria to identify such patients.

MATERIALS AND METHODS

A two-method strategy of gel testing (GT) and tube testing (TT) was used for Rh typing of patients with no historical blood type in the present institution. A monoclonal-polyclonal blend anti-D was used for Rh typing by TT at immediate spin. Three empirical criteria were used to identify candidates for genotyping: C1: discrepancy between the two test methods and a GT reaction strength >2+ stronger than TT; C2: weak serological reaction, defined as reaction strength ≤2+ regardless of testing method if both GT and TT were performed or reaction strength ≤2+ if only GT was performed, or reaction strength ≤1+ if only TT was performed; C3: presence of anti-D in D-positive patients with no history of RhIG use in the preceding 3 months and in whom alloanti-D is suspected.

RESULTS

Overall, 50 patients, ranging from newly born to 93 years old, were identified. Genomic testing confirmed D variants in 49/50 cases with a positive predictive value of 98%.

DISCUSSION

This two-method strategy is a powerful screening tool for identifying candidates for RHD genotyping. This strategy meets the current requirements of two blood type determinations/two specimens in pre-transfusion testing while simultaneously identifying candidates for RHD genotyping with a minimal increase in work load and cost.

Transfusion strategy for weak D Type 4.0 based on RHD alleles and RH haplotypes in Tunisia

BACKGROUND

With more than 460 RHD alleles, this gene is the most complex and polymorphic among all blood group systems. The Tunisian population has the largest known prevalence of weak D Type 4.0 alleles, occurring in one of 105 RH haplotypes. We aimed to establish a rationale for the transfusion strategy of weak D Type 4.0 in Tunisia.

STUDY DESIGN AND METHODS

Donors were randomly screened for the serologic weak D phenotype. The RHD coding sequence and parts of the introns were sequenced. To establish the RH haplotype, the RHCE gene was tested for characteristic single-nucleotide positions.

RESULTS

We determined all RHD alleles and the RH haplotypes coding for the serologic weak D phenotype among 13,431 Tunisian donations. A serologic weak D phenotype was found in 67 individuals (0.50%). Among them, 60 carried a weak D Type 4 allele: 53 weak D Type 4.0, six weak D Type 4.2.2 (DAR), and one weak D Type 4.1. An additional four donors had one variant allele each: DVII, weak D Type 1, weak D Type 3, and weak D type 100, while three donors showed a normal RHD sequence. The weak D Type 4.0 was most often linked to RHCE*ceVS.04.01, weak D Type 4.2.2 to RHCE*ceAR, and weak D Type 4.1 to RHCE*ceVS.02, while the other RHD alleles were linked to one of the common RHCE alleles.

CONCLUSIONS

Among the weak D phenotypes in Tunisia, no novel RHD allele was found and almost 90% were caused by alleles of the weak D Type 4 cluster, of which 88% represented the weak D Type 4.0 allele. Based on established RH haplotypes for variant RHD and RHCE alleles and the lack of adverse clinical reports, we recommend D+ transfusions for patients with weak D Type 4.0 in Tunisia.

Serological weak D phenotypes: a review and guidance for interpreting the RhD blood type using the RHD genotype

Approximately 0·2-1% of routine RhD blood typings result in a "serological weak D phenotype." For more than 50 years, serological weak D phenotypes have been managed by policies to protect RhD-negative women of child-bearing potential from exposure to weak D antigens. Typically, blood donors with a serological weak D phenotype have been managed as RhD-positive, in contrast to transfusion recipients and pregnant women, who have been managed as RhD-negative. Most serological weak D phenotypes in Caucasians express molecularly defined weak D types 1, 2 or 3 and can be managed safely as RhD-positive, eliminating unnecessary injections of Rh immune globulin and conserving limited supplies of RhD-negative RBCs. If laboratories in the UK, Ireland and other European countries validated the use of potent anti-D reagents to result in weak D types 1, 2 and 3 typing initially as RhD-positive, such laboratory results would not require further testing. When serological weak D phenotypes are detected, laboratories should complete RhD testing by determining RHD genotypes (internally or by referral). Individuals with a serological weak D phenotype should be managed as RhD-positive or RhD-negative, according to their RHD genotype.

Pre- and Post-Transfusion Alloimmunization in Dogs Characterized by 2 Antiglobulin-Enhanced Cross-match Tests

BACKGROUND

When dogs are transfused, blood compatibility testing varies widely but may include dog erythrocyte antigen (DEA) 1 typing and rarely cross-matching.

OBJECTIVES

Prospective study to examine naturally occurring alloantibodies against red blood cells (RBCs) and alloimmunization by transfusion using 2 antiglobulin-enhanced cross-match tests.

ANIMALS

Eighty client-owned anemic, 72 donor, and 7 control dogs.

METHODS

All dogs were typed for DEA 1 and some also for DEA 4 and DEA 7. Major cross-match tests with canine antiglobulin-enhanced immunochromatographic strip and gel columns were performed 26-129 days post-transfusion (median, 39 days); some dogs had an additional early evaluation 11-22 days post-transfusion (median, 16 days). Plasma from alloimmunized recipients was cross-matched against RBCs from 34 donor and control dogs.

RESULTS

The 2 cross-match methods gave entirely concordant results. All 126 pretransfusion cross-match results for the 80 anemic recipients were compatible, but 54 dogs died or were lost to follow up. Among the 26 recipients with follow-up, 1 dog accidently received DEA 1-mismatched blood and became cross-match-incompatible post-transfusion. Eleven of the 25 DEA 1-matched recipients (44%) became incompatible against other RBC antigens. No naturally occurring anti-DEA 7 alloantibodies were detected in DEA 7- dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

The antiglobulin-enhanced immunochromatographic strip cross-match and laboratory gel column techniques identified no naturally occurring alloantibodies against RBC antigens, but a high degree of post-transfusion alloimmunization in dogs. Cross-matching is warranted in any dog that has been previously transfused independent of initial DEA 1 typing and cross-matching results before the first transfusion event.

RHD alleles among pregnant women with serologic discrepant weak D phenotypes from a multiethnic population and risk of alloimmunization

BACKGROUND

A considerable number of RHD alleles responsible for weak and partial D phenotypes have been identified. Serologic determination of these phenotypes is often doubtful and makes genetic analysis of RHD gene highly desirable in transfusion recipients and pregnant women. We analyzed the RHD gene in a cohort of pregnant women with doubtful D phenotypes.

METHODS

RHD genotyping was performed on 104 cases with D typing discrepancies or with history of serologic weak D phenotype. Laboratory-developed DNA tests, RHD BeadChip (Bioarray Solutions, Immucor), and sequencing were used to identify the RHD alleles.

RESULTS

Molecular analyses showed 23 of 104 (22%) pregnant women were RHD*weak D types 1, 2, or 3 and not at risk for anti-D. Fifty-one (49%) were RHD*weak partial 4.0, 6 RHD*weak D type 38 (6%), 1 RHD*weak D type 45 (1%), 1 RHD*weak D type 67 (1%), and potentially at risk for being alloimmunized and making anti-D. Partial D was identified in 22 of 104 (21%) patients and definitively at risk for anti-D.

DISCUSSION

Appropriate classification of RhD phenotypes is recommended for correct indication of RhIG in pregnant women. However, the serologic distinction between RhD-negative and RhD-positive phenotypes is a difficult task in the case of D variants due to the variations in serologic testing. Our results show a great variability in RHD variant alleles in pregnant women from this population of high admixture. According to these results, 78% of these obstetric patients are at risk for anti-D and candidates for RhIG.

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.

Clinically relevant RHD-CE genotypes in patients with sickle cell disease and in African Brazilian donors

BACKGROUND

As a consequence of the homology and opposite orientation of RHD and RHCE, numerous gene rearrangements have occurred in Africans and resulted in altered RH alleles that predict partial antigens, contributing to the high rate of Rh alloimmunisation among patients with sickle cell disease (SCD). In this study, we characterised variant RH alleles encoding partial antigens and/or lacking high prevalence antigens in patients with SCD and in African Brazilian donors, in order to support antigen-matched blood for transfusion.

MATERIAL AND METHODS

RH genotypes were determined in 168 DNA samples from SCD patients and 280 DNA samples from African Brazilian donors. Laboratory developed tests, RHD BeadChip(TM), RHCE BeadChip(TM), cloning and sequencing were used to determine RHD-CE genotypes among patients and African Brazilian blood donors.

RESULTS

The distributions of RHD and RHCE alleles in donors and patients were similar. We found RHCE variant alleles inherited with altered RHD alleles in 25 out of 168 patients (15%) and in 22 out of 280 (7.8%) African Brazilian donors. The RHD and RHCE allele combinations found in the population studied were: RHD*DAR with RHCE*ceAR; RHD*weak D type 4.2.2 with RHCE*ceAR, RHD*weak D type 4.0 with RHCE*ceVS.01 and RHCE*ceVS.02; RHD*DIIIa with RHCE*ceVS.02. Thirteen patients and six donors had RHD-CE genotypes with homozygous or compound heterozygous alleles predicting partial antigens and/or lacking high prevalence antigens. Eleven patients were alloimmunised to Rh antigens. For six patients with RHD-CE genotypes predicting partial antigens, no donors with similar genotypes were found.

DISCUSSION

Knowledge of the distribution and prevalence of RH alleles in patients with SCD and donors of African origin may be important for implementing a programme for RH genotype matching in SCD patients with RH variant alleles and clinically significant Rh antibodies.

Variant RHD Types in Brazilians With Discrepancies in RhD Typing

BACKGROUND

The knowledge of D variants in patients and donors is important because anti-D alloimmunization can occur in some but not all individuals who express a variant RHD allele. Serologic distinction of RhD discrepancies is not always straightforward, which makes molecular analysis highly desirable.

METHODS

A group of 223 subjects, 129 patients, and 94 blood donors was identified and analyzed on the basis of a D typing discrepancy. The D antigen expression was evaluated by tube and gel hemagglutination with four anti-D reagents. PCR-single specific primer (SSP), multiplex PCR, RHD BeadChip (Immucor), or sequencing were used for molecular analysis.

RESULTS

In total, 168/223 (75%) weak D and 55/223 (25%) partial D variants were identified. Hemagglutination results varied in methods and anti-D reagents used in this process. There was no standard serologic reactivity identified, which could predict what type of D variant would be identified. Among weak D samples, types 1-3 were the most common, while DAR and DVI were most prevalent among partial D samples.

CONCLUSION

Our results show that discrepancies found in the serologic typing should be investigated by molecular methods in order to determine the D variant involved and also to distinguish between weak D and partial D. The knowledge of the distribution of weak D types and partial D among populations is important for D- patients and pregnant women management.

Prevalence of RhD status and clinical application of non-invasive prenatal determination of fetal RHD in maternal plasma: a 5 year experience in Cyprus

BACKGROUND

After the discovery that cell-free fetal DNA (cffDNA) is circulating in the maternal plasma of pregnant women, non-invasive prenatal diagnosis for fetal RhD in maternal plasma in RhD negative women at risk for haemolytic disease of the newborn (HDN) was clinically established and used by many laboratories. The objectives of this study are: (a) to assess the feasibility and report our experiences of the routine implementation of fetal RHD genotyping by analysis of cffDNA extracted from maternal plasma of RhD negative women at risk of HDN, and (b) to estimate the RhD phenotype frequencies, the RHD genotype frequencies and the RhD zygosity in the Cypriot population.

METHODS

cffDNA was extracted from maternal plasma of 73 RhD negative pregnant women. Real-Time Multiplex-PCR was used to amplify regions of RHD gene in exons 4, 5 and 10. RhD phenotypes were determined on 445 random samples using conventional agglutination slide test.

RESULTS

The fetus was predicted to be positive in 53 cases and negative in 18 cases. Two of cases were identified as D-variants, weak D type-1 and 11. The frequency of RhD negative homozygosity in the Cypriot population was estimated to be 7.2%, while the frequencies of RHD hemizygosity and RhD positive homozygosity was calculated to be 39.2 and 53.6%, respectively.

CONCLUSION

Fetal RHD genotyping can be accurately determined using cffDNA from maternal plasma. The implementation of the test has eliminated all use of unnecessary anti-D and reduced the total use of anti-D by 25.3% while achieving appropriate management of the RhD negative pregnancies.

Advances in Blood Typing

The clinical importance of blood group antigens relates to their ability to evoke immune antibodies that are capable of causing hemolysis. The most important antigens for safe transfusion are ABO and D (Rh), and typing for these antigens is routinely performed for patients awaiting transfusion, prenatal patients, and blood donors. Typing for other blood group antigens, typically of the Kell, Duffy, Kidd, and MNS blood groups, is sometimes necessary, for patients who have, or are likely to develop antibodies to these antigens. The most commonly used typing method is serological typing, based on hemagglutination reactions against specific antisera. This method is generally reliable and practical for routine use, but it has certain drawbacks. In recent years, molecular typing has emerged as an alternative or supplemental typing method. It is based on detecting the polymorphisms and mutations that control the expression of blood group antigens, and using this information to predict the probable antigen type. Molecular typing methods are useful when traditional serological typing methods cannot be used, as when a patient has been transfused and the sample is contaminated with red blood cells from the transfused blood component. Moreover, molecular typing methods can precisely identify clinically significant variant antigens that cannot be distinguished by serological typing; this capability has been exploited for the resolution of typing discrepancies and shows promise for the improved transfusion management of patients with sickle cell anemia. Despite its advantages, molecular typing has certain limitations, and it should be used in conjunction with serological methods.

Hemolytic disease of the fetus and newborn: managing the mother, fetus, and newborn

Hemolytic disease of the fetus and newborn (HDFN) affects 3/100 000 to 80/100 000 patients per year. It is due to maternal blood group antibodies that cause fetal red cell destruction and in some cases, marrow suppression. This process leads to fetal anemia, and in severe cases can progress to edema, ascites, heart failure, and death. Infants affected with HDFN can have hyperbilirubinemia in the acute phase and hyporegenerative anemia for weeks to months after birth. The diagnosis and management of pregnant women with HDFN is based on laboratory and radiographic monitoring. Fetuses with marked anemia may require intervention with intrauterine transfusion. HDFN due to RhD can be prevented by RhIg administration. Prevention for other causal blood group specificities is less studied.

A model for integrating molecular-based testing in transfusion services

BACKGROUND

Molecular-based laboratory tests can predict blood group antigens and supplement serological methods, adding a unique technology to assist in resolving discrepant or incomplete blood group typing or antibody identification. Hospital transfusion services have options for integrating molecular-based methods in their routine operations. We describe here the model of a hospital-reference laboratory partnership.

MATERIALS AND METHODS

Blood samples for compatibility testing were obtained from patients in a 609-bed hospital serving an urban multiethnic and multiracial population. When results of blood group phenotyping by serological methods were inconclusive, samples were referred for molecular-based testing. The reference laboratory used several methods for genotyping, including polymerase chain reaction followed by restriction enzyme-linked polymorphism analysis, sequence-specific primer polymerase chain reaction and array-based approaches. Human erythrocyte antigen, RHCE and RHD single nucleotide polymorphism arrays were integrated into the laboratory as they became commercially available.

RESULTS

The hospital-reference laboratory model made it possible to integrate blood group genotyping promptly by current technology without the expense of new laboratory equipment or adding personnel with technical expertise. We describe ten cases that illustrate the categories of serological problems that were resolved by molecular methods.

DISCUSSION

In-hospital molecular testing for transfusion services has logistical advantages, but is financially impractical for most hospitals. Our model demonstrates the advantages of a hospital-reference laboratory partnership. In conclusion, hospital transfusion services can integrate molecular-based testing in their routine services without delay by establishing a partnership with a molecular blood group reference laboratory. The hospital reference-laboratory model promotes genomic medicine without the expense of new equipment and skilled personnel, while supporting the economy of centralised large-scale laboratory operations.

RHD genotyping and its implication in transfusion practice

BACKGROUND

The limitations of serology can be overcome by molecular typing. In order to evaluate the contribution of RH systematic genotyping and its implication in transfusion practice, a genotyping of D- blood donors was initiated.

METHODS

Blood samples were collected from 400 unrelated D- individuals. All samples were tested by RHD exon 10 PCR. In order to clarify the molecular mechanisms of RHD gene carrier, we applied molecular tools using different techniques: PCR-multiplex, and PCR-SSPs.

RESULTS

Among 400 D- subjects tested, 390 had RHD gene deletion; and 10 had RHD exon 10 of which seven were associated with the presence of the C or E antigens. Among D- carriers, we observed in five cases the presence of RHD-CE-Ds hybrid, in four cases the presence of pseudogene RHD ψ and in one case the presence of weak D type 4.

CONCLUSION

Since the majority of aberrant alleles were associated with C or E antigens and the preliminary infrastructure for molecular diagnostic were absent in all Tunisia territory, we recommend to reinforce transfusion practice to consider D- donors but C+/E+ antigens as D+ donors and the application of RHD molecular typing only to solve serologic problems.

RHD positive among C/E+ and D-negative blood donors in Tunisia

PURPOSE OF THE STUDY

The aim of this study was to investigate RHD alleles among Tunisian blood donors with D-negative phenotype and positive for C and/or E antigen.

PATIENTS AND METHODS

A total of 100 D-negative and C/E+ samples were analyzed by RHD genotyping using an initial test for RHD exon 10. In case of a positive reaction, further molecular investigations including real time quantitative PCR, allele specific PCR and nucleotide sequencing were done to elucidate the RHD involved mechanisms.

RESULTS

Seventy-five percent of the studied samples lacked the RHD gene. Twenty-three percent carried the hybrid RHD-CE-D alleles (16 RHD-CE(3-7)-D, 5 RHD-CE(4-7)-D, 1 RHD-CE(4-8)-D, 1 RHD-CE(3-8)-D) and 2% were weak D (1 weak D type 1 and 1 weak D type 5).

CONCLUSION

Our study proved the high frequency of RHD gene among serologically D-negative samples, positive for C and/or E antigen. Thus achieving systematically RHCE phenotyping in all transfusion centers on the Tunisian territory and considering blood donated from D-negative C/E+ persons as D-positive will be recommended to reduce anti-D allo-immunization.

Serologic findings of RhD alleles in Egyptians and their clinical implications

INTRODUCTION

Serologic discrepancies caused by various reactivity of D variants can only be resolved by the use of RhD genotyping. However, this strategy cannot be applied routinely due to the cost and feasibility. It has been documented that D variants are demonstrated among individuals with positivity for at least C or E antigens. It is considered to be affordable for some countries to test D negative donors who are C or E positive for D variants. It was proposed that an algorithm could be found based on distinct serologic features that matches the Egyptian genetic frequency data, and correctly assigns donors and patients, using the least possible expenses.

MATERIALS AND METHODS

Samples with the most prevalent weak D and partial D were investigated for their RhCE phenotype. Routine D typing by immediate spin (IS) tube method was performed in parallel with an automated gel test, and the reactivity results of D variants with both techniques were compared.

RESULTS

Among 31 D variants, only 5 were C or E positive (16.1 %). R0r phenotype was associated with the remaining 26 samples (83.9%) and constituted weak D types 4.2 (38.5%), and 4.0/4.1 (11.5%), partial DIII (34.6%), and partial DV (15.4%). Gel reacted strongly with partial DIII and DV. Ten samples with DIII and DV typed as D positive with IS. All weak D were positive by indirect antiglobulin test (IAT), while all partial D were positive by gel and IAT.

CONCLUSION

Guidelines for RhD workup should be adjusted to match population data. Detection of D variants among C or E positive donors may not be an optimal strategy for Egyptians. Serology cannot discriminate weak D from partial D, but may provide a clue about the probable D variant to be tested molecularly with the appropriate kit. Reagent selection is important to correctly assign donors and patients with the DIII and DV types.