Prenatal determination of fetal RhD type by DNA amplification

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.

Severe hemolytic disease of the fetus and newborn due to allo-anti-D in a patient with a partial DEL phenotype arising from the variant allele described as RHD*148+1T (RHD*01EL.31)

BACKGROUND

RhD DEL variants may show complete or partial expression of RhD epitopes. There have been only rare reports of anti-D causing hemolytic disease of the fetus and newborn (HDFN) in this context. We report a case of severe HDFN associated with a recently described DEL variant.

CASE REPORT

A multiparous woman presented with an allo-anti-D and showed incongruent phenotyping and genotyping results on initial study. Further investigations identified the RHD mutation, defined as RHD*148+1T and named RHD*01EL.31, which had been previously associated with a DEL phenotype. Extended RhD phenotyping by adsorption-elution showed that there was reactivity with four of nine monoclonal anti-D antibodies, suggesting a partial DEL phenotype. The first child showed no clinical evidence of HDFN, although the cord direct antiglobulin test was positive. The second child developed fetal anemia treated with intrauterine transfusion, and neonatal hyperbilirubinemia requiring exchange transfusion.

CONCLUSION

The RHD allele, RHD*148+1T, results in a partial Del phenotype, and the anti-D formed in pregnant women with this phenotype is capable of causing severe HDFN.

Considerations of red blood cell molecular testing in transfusion medicine

The field of transfusion medicine is on the threshold of a paradigm shift, as the technology for genotyping of red blood cell antigens, including US FDA-approved arrays, is now moving into standard practice. Access to cost-efficient, high-resolution genotyping has the potential to increase the quality of care by decreasing the risk for alloimmunization and incompatible transfusions in individuals on long-term blood transfusion protocols, including patient groups with hemoglobinopathies and other chronic diseases. Current and future applications of molecular methods in transfusion medicine and blood banking are discussed, with emphasis on indications for genotyping in various clinical scenarios. Furthermore, limitations of the current gold standard methodology and serology, as well as of contemporary molecular methodology, are examined.

[Non-invasive fetal RHD genotyping: Validation of the method with 200 patients]

BACKGROUND

Non-invasive fetal RHD genotyping is an important tool to assess the risk of fetuse's hemolytic disease of anti-D allo-immunized pregnant woman by non-invasive method. A method of genotyping has been developed in the laboratory of Lyon-GHE according to Minon's team (J Gynecol Obstet Biol Reprod 2005): exon 4, 5, and 10 are amplified by real time PCR. At first, genotyping results of 200 pregnant women have been compared with RH1 phenotype at birth. The most important parameters of validation have been tested: the sensibility and the specificity; the negative predictive value; the correlation study permitted to define criteria of biological interpretation. The validation of this method permitted to determine critical points and the limits of the method due to the minor amount of fetal DNA in the maternal plasma and existence of many variant forms of the RHD gene.

CONCLUSION

We worked too in the perspective to the accreditation for our genetic laboratory.

Rhesus-D zygosity and hemolytic disease of fetus and newborn

Alloimmunization against the Rhesus-D (RhD) antigen still remains as a major cause of hemolytic disease of fetus and newborn (HDFN). Determination of paternal RhDzygosity is performed by molecular testing and is valuable for the management of alloimmunized pregnant women. A 30-year-old pregnant woman with AB negative blood group presented with two consecutive abortions and no history of blood transfusion. By application of the antibody screening, identification panel, and selected cells, she was found to be highly alloimmunized. RhDzygosity was performed on her partner and was shown to be homozygous for RhD. The sequence- specific priming-polymerase chain reaction used in this report is essential to establish whether the mother requires an appropriate immunoprophylaxis or the fetus is at risk of HDFN.

RHD alleles in the Tunisian population

Background:

A comprehensive survey of RHD alleles in Tunisia population was lacking. The aim of this study was to use a multiplex RHD typing assay for simultaneous detection of partial D especially with RHD/RHCE deoxyribonucleic acid (DNA) sequence exchange mechanism and some weak D alleles.

Materials and Methods:

Six RHD specific primer sets were designed to amplify RHD exons 3, 4, 5, 6, 7 and 9. DNA from 2000 blood donors (1777 D+ and 223 D-) from several regions was selected for RHD genotyping using a PCR multiplex assay. Further molecular investigations were done to characterize the RHD variants that were identified by the PCR multiplex assay.

Results:

In the 1777 D+ samples, only 10 individuals showed the absence of amplification of exons 4 and 5 that were subsequently identified by PCR-SSP as weak D type 4 variants. No hybrid allele was detected. In the 223 D-, RHD amplification of some exons was observed only in 5 samples: 4 individuals expressed only RHD exon 9, and one subject lacking exons 4 and 5. These samples were then screened by PCR-SSPs on d(C) ce^s and weak D type 4, respectively.

Conclusion:

The weak D type 4 appears to be the most common D variant allele. We have not found any partial D variant. Findings also indicated that RHD gene deletion is the most prevalent cause of the D- phenotype in the Tunisian population.

RHD PCR of D-Negative Blood Donors

SUMMARY

RHD PCR of blood donors may be used to reveal weak D, partial D, DEL and chimeric D+/D- donors among presumed D-negative blood donors. Units donated by such donors pose a definite yet low risk for anti-D immunization of transfusion recipients. The frequency of DEL donors among D-negative donors is 1:350 to 1:2,000 in Europe and up to 1:5 in Asian countries. Different strategies for RHD PCR of blood donors have been used. Probably, the most cost-efficient implementation is replacement of sensitive D antigen testing with the indirect antiglobulin test by RHD PCR in pools which might even reduce total testing cost.

Circulating cell-free fetal DNA for the detection of RHD status and sex using reflex fetal identifiers

OBJECTIVE

To determine the sensitivity and specificity of circulating cell-free fetal DNA in determining the fetal RHD status and fetal sex.

METHODS

Maternal blood was collected in each trimester of pregnancy from RhD negative nonalloimmunized women. Whole blood was centrifuged, separated into plasma and buffy coat, and frozen at -80°C. DNA analysis was conducted via allele-specific primer extensions for exons 4, 5, and 7 of the RHD gene and for a 37-base pair insertion in exon 4 (RHD pseudogene; psi) three Y-chromosome sequences (SRY, DBY, and TTY2), and an extraction control (TGIFL-like X/Y). RhD serotyping on cord blood and gender assessment of the newborns were entered into a Web-based database.

RESULTS

One hundred twenty women were enrolled. The median gestational age at the first venipuncture was 12.4 (range: 10.6-13.9) weeks with 120 samples drawn; 118 samples were drawn at 17.6 (16-20.9) weeks; and 113 samples at 28.7 (27.9-33.9) weeks. Overall accuracy for RHD was 99.1%, 99.1%, and 98.1% for each trimester and was 99.1%, 99.1%, and 100% for fetal sex determination.

CONCLUSIONS

Fetal RHD genotyping and sex can be very accurately determined in all three trimesters using circulating cell-free fetal DNA in the maternal circulation.

From prenatal genomic diagnosis to fetal personalized medicine: progress and challenges

Thus far, the focus of personalized medicine has been the prevention and treatment of conditions that affect adults. Although advances in genetic technology have been applied more frequently to prenatal diagnosis than to fetal treatment, genetic and genomic information is beginning to influence pregnancy management. Recent developments in sequencing the fetal genome combined with progress in understanding fetal physiology using gene expression arrays indicate that we could have the technical capabilities to apply an individualized medicine approach to the fetus. Here I review recent advances in prenatal genetic diagnostics, the challenges associated with these new technologies and how the information derived from them can be used to advance fetal care. Historically, the goal of prenatal diagnosis has been to provide an informed choice to prospective parents. We are now at a point where that goal can and should be expanded to incorporate genetic, genomic and transcriptomic data to develop new approaches to fetal treatment.

Detection of fetal RHD pseudogene (RHDΨ) and hybrid RHD-CE-Ds from RHD-negative pregnant women with a free DNA fetal kit

Hemolytic disease of the newborn is a clinical condition in which maternal and paternal Rh blood group antigens are incompatible and the mother is negative for the antigen whereas the father is positive. Analysis of fetal cells recovered from maternal plasma can provide a highly sensitive prenatal diagnosis. The fetal RHD gene in plasma DNA is detected by real-time PCR amplification of two different segments of the RHD gene (exons 7 and 10). Each amplicon is revealed with specific probes. We examined 40 female blood samples to verify the specificity of RHD exons (7 and 10) amplified by real-time PCR. Thirty fetuses were predicted to be RHD-positive based on analysis of plasma DNA. Seven fetuses were predicted to be RHD-negative. One fetus was negative for RHD on exon 10, and positive for RHD on exon 7 (early gestation age); two fetuses were RHD-negative on exon 7, and RHD-positive on exon 10 (RHD-CE-D(s) or RHDΨ), indicative of a maternal RHD allele. We conclude that it is necessary to analyze at least two exon regions in the RHD gene.

Non-invasive prenatal diagnosis using cell-free fetal nucleic acids in maternal plasma: Progress overview beyond predictive and personalized diagnosis

The discovery of circulating cell-free fetal DNA (cffDNA) in maternal plasma allowed for the development of alternative methodologies that may facilitate safe non-invasive prenatal diagnosis (NIPD). The low concentration of cffDNA in maternal plasma, however, and the coexistence of maternal DNA limit its clinical application to the detection or exclusion of fetal targets that are not present in the mother, such as Y chromosome sequences, the RHD gene in a RhD-negative woman and genetic conditions inherited from the father. Strategies for NIPD of monogenic disorders and fetal chromosomal aneuploidies have also been achieved using next-generation sequencing and could be introduced to the clinics as soon as cost-effective and high throughput protocols are developed.

Noninvasive approach for the management of hemolytic disease of the fetus

Hemolytic disease of the fetus and newborn (HDFN) is due to maternal alloantibodies directed against paternally inherited antigens on fetal red cells, and it is still a problem in affected pregnancies despite the routine use of anti-D immunoglobulin during pregnancy and shortly after delivery. The current noninvasive management of HDFN starts with the determination of fetal RhD genotype by use of cell-free fetal DNA in maternal plasma. When the fetus is antigen positive, the follow-up is performed by Doppler ultrasonography for the detection of moderate or severe anemia on the basis of an increase peak velocity of systolic blood in the middle cerebral artery. Finally, if anemia is suspected, an invasive approach is required in order to perform an intrauterine blood transfusion, which should only be attempted when the fetus needs transfusion. This approach reduces the iatrogenic conversion of mild-to-severe disease, which occurred as a result of the previous invasive management, and prevents unnecessary administration of human-derived blood products. These changes represent one of the genuine successes of fetal therapy.

Cell-free fetal DNA in the maternal serum and plasma: current and evolving applications

PURPOSE OF REVIEW

Free fetal nucleic acids, found in the plasma of every pregnant woman, have made a substantial impact on prenatal diagnosis. The past decade has seen the introduction of routine noninvasive prenatal diagnosis (NIPD) using DNA extracted from maternal plasma for a number of clinical complications of pregnancy, notably feto-maternal blood group incompatibility, fetal sexing and exclusion/detection of single-gene disorders. It appears that mass-scale analysis of all RhD-negative pregnant women will be adopted to conserve stocks of prophylactic anti-D and avoid the administration of a blood product unnecessarily. For the majority of prenatal diagnostic procedures, the assessment of trisomy, particularly trisomy 21, is the highest priority. Because RHD genotyping, fetal sexing and analysis of single-gene disorders all depend on the detection of paternally inherited alleles, they were relatively simple to adapt on the basis of PCR analysis of DNA obtained from maternal plasma. However, for assessment of chromosome copy number, this is not so straightforward.

RECENT FINDINGS

The assessment of polymorphisms among placentally expressed mRNAs found in maternal plasma has enabled the detection of trisomy 21 fetuses using a combination of reverse transcriptase PCR and mass spectrometry to define allelic ratios of maternally and paternally inherited single nucleotide polymorphisms. Interesting recent developments also include the finding that direct sequence analysis of maternal plasma extracted DNA using 'next-generation' DNA sequencers can differentiate between normal and trisomy fetuses.

SUMMARY

NIPD using nucleic acids obtained from maternal plasma and serum is now a clinical reality, particularly in the management of hemolytic disease of the fetus and newborn. Recent advances signal that NIPD for common aneuploidies will soon be possible.

The Bloodgen Project of the European Union, 2003-2009

The Bloodgen project was funded by the European Commission between 2003 and 2006, and involved academic blood centres, universities, and Progenika Biopharma S.A., a commercial supplier of genotyping platforms that incorporate glass arrays. The project has led to the development of a commercially available product, BLOODchip, that can be used to comprehensively genotype an individual for all clinically significant blood groups. The intention of making this system available is that blood services and perhaps even hospital blood banks would be able to obtain extended information concerning the blood group of routine blood donors and vulnerable patient groups. This may be of significant use in the current management of multi-transfused patients who become alloimmunised due to incomplete matching of blood groups. In the future it can be envisaged that better matching of donor-patient blood could be achieved by comprehensive genotyping of every blood donor, especially regular ones. This situation could even be extended to genotyping every individual at birth, which may prove to have significant long-term health economic benefits as it may be coupled with detection of inborn errors of metabolism.

Large-scale blood group genotyping: clinical implications

The molecular background of blood group antigen expression of the major clinically significant blood group antigens has been largely accomplished. Despite this large body of work, blood group phenotype prediction by genotyping has a marginal supporting role in the routine blood bank. It has however had a major impact in the prenatal determination of fetal blood group status in the management of haemolytic disease of the fetus and newborn. In the past few years several high throughput systems have been in development that have the potential capacity to perform genotyping on a mass scale. Such systems have been designed for use on donor- and patient-derived DNA and provide much more comprehensive information regarding an individuals blood group than is possible by using serological methods alone. DNA-based typing methodology is easier to standardize than serology and has the potential to replace it as a front line diagnostic in blood banks. This review overviews the current situation in this area and attempts to predict how blood group genotyping will evolve in the future.

Polymerase chain reaction and its use in obstetrics

Deoxyribonucleic acid (DNA) is composed of a deoxyribose backbone, the three position (3') of each deoxyribose being linked to the five position (5') of the next by a phosphodiester bond. At the two position each deoxyribose is linked to one of four nucleic acids; the purines adenine or guanine or the pyrimadines thymine or cytosine. Each DNA molecule is made up of two such strands in a double helix with the nucleic acid bases on the inside. The bases pair by hydrogen bonding, adenine (A) with thymine (T) and cytosine (C) with guanine (G). Deoxyribonucleic acid is replicated by separation of the two strands and synthesis by DNA polymerases of new complementary strands. With one notable exception, the reverse transcriptase produced by viruses, DNA polymerases always add new bases at the 3' end of the molecule. Ribonucleic acid (RNA) has a structure similar to that of DNA but is always single stranded. The backbone consists of ribose, and uracil is used in place of thymine.

The changing face of haemolytic disease of the newborn

The diagnosis, acute management and follow-up of neonates with haemolytic disease of the newborn (HDN) still represents a significant area of activity for maternity/neonatal services. ABO incompatability is now the single largest cause of HDN in the western world. However, with increasing knowledge at the molecular level, and closer liaison between neonatal paediatricians and haematologists, the diagnosis of non-immune causes of HDN is increasing. As these conditions have an inherited basis and therefore have implications for other family members (or future children), it remains a high priority for all neonatal paediatricians to achieve an accurate diagnosis in all cases of HDN. As the efficacy of phototherapy increases the role of exchange transfusion in acute management is rapidly decreasing. This makes gauging the appropriate time to intervene with exchange transfusion a difficult clinical decision, and guidelines appropriate to the spectrum of contemporary disease are required. In the future intravenous immunoglobulin and/or intramuscular metalloporphyrins may further reduce the need for exchange transfusion and continue to change the spectrum of HDN faced by neonatal paediatricians.

Noninvasive fetal RHD genotyping from maternal plasma. Use of a new developed Free DNA Fetal Kit RhD

Fetal RHD genotyping from maternal plasma was performed by real-time PCR amplification of exons 7 and 10 of the RHD gene and the amplified products were detected either with SYBR Green I dye according to our previously published method [Mol Diagn 8 (2004) 23-31] or with hydrolysis probes in a new Free DNA Fetal Kit RhD((R)). Plasma specimen from 300 RhD-negative pregnant women (between 10 to 34 weeks of gestation) were analysed and validation of the results was ascertained either by RHD genotyping on amniotic cells or by blood typing of the neonate at birth. We found 100% concordant results when comparing the two methods. Two false-positive but no false-negative results were found. Thus, the sensitivity of the assay was 100% and the specificity superior than 99%. These data confirm the accuracy of fetal RHD genotyping on maternal plasma using the Free DNA Fetal Kit RhD, thus allowing to propose non invasive PCR-based fetal RHD genotyping for all RhD-negative pregnant women and to restrict the use of anti-D immunoglobulins only to those bearing an RhD-positive fetus.

Predictive blood group genetics in hemolytic disease of the fetus and newborn: a 10-year review of a laboratory evaluation of amniotic fluid-derived DNA

OBJECTIVE

To identify the types of requests, the patterns of testing, and the error rates associated with the genetic identification of fetuses at risk for immune-mediated hemolytic disease.

METHOD

Retrospective review of the laboratory information system for all fetal blood group genotyping tests performed at Mount Sinai Hospital, Toronto, Canada from January 1997 to December 2006.

RESULTS

Amniotic fluid-derived DNA, from 220 women (243 pregnancies), was tested for one or more antigens (279 tests) when the father was heterozygous for the inferred blood group antigen or was unavailable. The PCR amplification failure rate of amniotic fluid-derived DNA was 5.0%. When the father was considered hemizygous for RHD or was not available, the fetus was positive in 68.6% and 72.7% of cases, respectively. Two amniotic fluid-derived DNA KEL1 SSP-PCR results did not correlate with the result determined from cultured amniocyte DNA.

CONCLUSIONS

Paternal RHD hemizygosity may be overestimated. Thus, we recommend that RHD zygosity be established by molecular analysis of the RHD breakpoint. Cultured amniocytes should be reserved for testing if the amniotic fluid-derived DNA is inconclusive due to PCR amplification failure. We use PCR-RFLP genotyping methods for RHCE*E/RHCE*e (Rh E/e), KEL1/KEL2 (K/k), FYA/FYB (Fy(a/b)), and JKA/JKB (Jk(a/b)).

Rh discrepancies caused by variable reactivity of partial and weak D types with different serologic techniques

BACKGROUND

RhD discrepancies between current and historical results are problematic to resolve. The investigation of 10 discrepancies is reported here.

STUDY DESIGN

Samples identified were those that reacted by automated gel technology and were negative with an FDA-approved reagent. Reactivity with a commercially available panel of monoclonal anti-D was performed. Genomic DNA was evaluated for RHD alleles with multiplex RHD exon polymerase chain reaction (PCR), weak D PCR-restriction fragment length polymorphism, and RHD exon 5 and 7 sequence analyses.

RESULTS

The monoclonal anti-D panel identified two samples as DVa, yet possessed the DAR allele. Two weak D Type 1 samples had a similar monoclonal anti-D profile, but only one reacted directly with one of two FDA-approved anti-D. Only two of four weak D Type 2 samples reacted directly with one FDA-approved anti-D, and their D epitope profile differed.

CONCLUSIONS

The monoclonal anti-D reagents did not distinguish between partial and weak D Types 1 and 2. Weak D Types 1 and 2 do not show consistent reactivity with FDA-approved reagents and technology. To limit anti-D alloimmunization, it is recommended that samples yielding an immediate-spin tube test cutoff score of not more than 5 (i.e., < or =1+ agglutination) or a score of not more than 8 (i.e., < or =2+ hemagglutination) by gel technology be considered D- for transfusion and Rh immune globulin prophylaxis. That tube test anti-D reagents react poorly with some Weak D Types 1 and 2 red cells is problematic, inasmuch as they should be considered D+ for transfusion and prenatal care. Molecular tests that distinguish common partial and Weak D types provide the solution to resolving D antigen discrepancies.

Fetal anaemia: diagnosis and management

Fetal anaemia can by treated by in-utero therapy, which results in a significant improvement in perinatal outcome. The important causes of fetal anaemia are rhesus alloimmunisation, kell alloimmunisation and parvovirus infection. At-risk pregnancies require serial monitoring to ensure timely intervention with intrauterine transfusion. Non-invasive testing with middle cerebral artery Doppler is becoming the monitoring modality of choice.

Blood group genotyping in Germany

BACKGROUND

Molecular methods for blood group genotyping became available more than 10 years ago as one major aspect of immunogenetics. Since then, the clinical applications have been expanded and refined. Their implementation varies considerably among different health-care systems, notably between North America and Europe.

STUDY DESIGN

This summary is based on studies published mostly during the last 3 years and on workshop reports from the German and Swiss transfusion societies. It represents an edited transcript of the author's presentation given at the Workshop on Molecular Methods in Immunohematology organized by the Food and Drug Administration (FDA) in Bethesda on September 25, 2006.

RESULTS

Current applications of blood group genotyping in Germany, Switzerland, and Austria are detailed: weak D testing in patients and pregnant women; blood group genotyping in perinatal care, in patients who received a transfusion, and in patients with immunohematologic problems; RHD genotyping in donors for DEL and D(+/-) chimera; and RHD zygosity testing.

CONCLUSION

Since around 2000, molecular tests for blood groups have been widely offered as a routine service. Many samples are shipped to reference laboratories in the German-speaking countries with the specific request for such testing. The advent of Conformité Européenne (CE)-labeled test kits renders it technically and legally possible, within the specifications of the CE-certification process for in vitro diagnostic devices in the European Union, to replace several blood group serology tasks by genotyping.

Molecular genetic blood group typing by the use of PCR-SSP technique

BACKGROUND

DNA-based methods are useful for enhancing immunohematology typings. Ready-to-use Conformité Européenne (CE)-marked test kits based on polymerase chain reaction with sequence-specific priming (PCR-SSP) have been developed, which enable the examination of weak, unexpected, or unclear serologic findings. DEVELOPMENT AND VALIDATION: Primers were designed according to established mutation databases. Proficiency testing for CE marking was performed in accordance with Directive 98/79EC of the European Parliament and of the Council of October 27, 1998 on in vitro diagnostic medical devices using pretyped in-house and external samples. INTENDED USE: BAGene PCR-SSP kits are in vitro diagnostic devices. Genotyping of ABO and RHD/RHCE as well as HPA and KEL, JK, and FY specificities has to be performed after the conclusion of the serologic determination.

APPLICATION

Ready-to-use PCR-SSP typing kits allow the determination of common, rare, or weak alleles of the ABO blood group, Rhesus, and Kell/Kidd/Duffy systems as well as alleles of the human platelet antigens.

RESULTS

The investigations showed clear-cut results in accordance with serology or molecular genetic pretyping.

CONCLUSION

PCR-SSP is a helpful supplementary technique for resolving most of the common problems caused by discrepant or doubtful serologic results, and it is an easy-to-handle robust method. Questionable cases in donor, recipient, and patient typing can be examined with acceptable cost.

Prenatal diagnosis of the Rhesus D fetal blood type on amniotic fluid in daily practice

OBJECTIVE

To retrospectively examine the diagnostic accuracy of prenatal RhD blood type genotyping on amniotic fluid, using a combination of two polymerase chain reaction (PCR) methods in daily practice.

METHODS

Amniotic fluid was obtained from women undergoing amniocentesis. Two PCR protocols were carried out in two different laboratories. We obtained the postnatal serological RhD status. In cases with differing prenatal and postnatal test results, we investigated the possible error source by different methods. Sensitivity, specificity and the predictive values were calculated.

RESULTS

Prenatal RhD genotyping was applied in 1,640 cases, of which the postnatal serologic RhD status was obtained in 927. No discordance between both PCR methods occurred. In nine out of 927 cases differing results between PCR and serologic status were encountered. The sensitivity was 99.5%, the specificity 98.6%, and both positive and negative predictive values 99.1%.

CONCLUSION

Prenatal diagnosis of the fetal RhD blood type with PCR from amniotic fluid is highly accurate in daily practice and associated with a minimal sensitivity of 99.5% and a minimal specificity of 98.6%.

Prenatal determination of the fetal RhD blood group by multiplex PCR: a 7-year Portuguese experience

OBJECTIVES

This is a retrospective study to evaluate the efficacy and accuracy of the multiplex polymerase chain reaction (PCR) amplification, for early detection of fetuses at risk for hemolytic disease, in the population living in Portugal, and to characterize the RhD-negative individuals at serologic and molecular level.

METHODS

2030 uncultured amniotic fluid samples and 2012 blood samples from the respective RhD-negative pregnant women were studied by multiplex PCR of intron 3/intron 4, exon 7 and 3'UTR. Amniocentesis was performed for a variety of medical indications. For quality control, serologic RhD blood groups were determined in the cord blood, after birth.

RESULTS

1361 fetal amniotic samples were RhD-positive (67%), 669 were RhD-negative. The average time for diagnosis was 2 days for uncultured amniocytes and the molecular versus serologic RhD typing (n = 809) had 99.5% concordance. Among the 2012 serologic RhD-negative mothers, 26 had an RhD-positive allele.

CONCLUSION

The multiplex PCR amplification used in this study was a rapid and accurate method to determine the RhD blood type in the population living in Portugal, being a great tool for management of pregnancies with fetuses at risk for alloimmune hemolytic disease. In this population, 1.3% of the serologic RhD-negative women have an RHD-positive allele.

Large scale blood group genotyping

Determination of predicted blood group phenotype by determination of genotype has been performed since the 1990s. This evolved due to the rapid accrual of information surrounding the molecular basis of blood group antigen expression, which started in 1990 with ABO and RH systems and has now resulted in the molecular description of 28 of the 29 blood groups. Blood group genotyping is currently performed mostly for fetal blood group incompatibility and for assessment of multi-transfused patients. Both of these clinical scenarios are either dangerous or technically difficult, respectively to define serologically. With the simultaneous development of mass scale genotyping platforms it has now permitted the application of them to blood group genotype determination. In this paper, I describe some recently published work that has demonstrated that mass scale genotyping approaches are feasible. These approaches may lead to more effective management of blood stocks and patient cross-matching by reducing the dependence on serology during the time critical pre-transfusion phase. It is most probable that large scale studies, perhaps involving many European Union and North American based blood suppliers, may drive the introduction of this technology and convince red cell serologists that this approach may allow their work to be more focussed.

La surveillance immunohématologique de la femme enceinte et la nouvelle politique de prévention de l’allo-immunisation anti-RH1

Despite the generalization of immunoprophylaxis by anti-RH immunoglobulins since 1970 and improved management of at-risk pregnancies, allo-immunization due to the RH1 antigen (formerly known as Rhesus D or Rh D) remains widespread. In fact, anti-RH1 antibodies currently constitute over one-third of the immune antibodies detected after pregnancy. At the same time, allo-immunizations against others antigens than anti-RH1, especially anti-RH4 (anti-c) and anti-KEL1 (anti-Kell) increase. Allo-immunization, its follow-up during pregnancy, and its prevention are therefore still topical, and concern all the pregnant women. Immunohematological tests used in antenatal patients have gone a long way. However, despite a great deal of progress, we should not loose sight of the fact that these tests give only an indirect measurement and will only help the obstetrician, in conjunction with other fetal parameters to assess the severity of the haemolytic disease. The best method to assess the severity is the determination of the level of fetal hemoglobin after fetal blood sampling but this procedure is not without risk. Since 13 years, it is possible to determine the fetal RHD genotype of using amniocytes and to day directly with maternal plasma. All pregnant women should be blood-typed for ABO-RH-KEL1 and the blood tested for clinically irregular antibodies. The trend in anti-RH levels is more important than the level itself. Manual titration is simple but only provides rough, semiquantitative estimates of anti-RH concentration. Quantitative hemagglutination methods, using auto-analyzers and appropriate anti-RH1 standards, measured in mug/ml, are sensitive, rapid and have acceptable intra-laboratory reproducibility. RH:-1 women who are non-sensitized against RH1 antigen during and at the end of their pregnancy with a RH1 child. RH prophylaxis includes targeted prophylaxis after feto-maternal hemorrhage and now routine antenatal RH prophylaxis at the 28th week of gestation. It has been necessary to synthesize the indications of RH prophylaxis and immunohematological tests to assure an efficient therapeutic prevention.

Haemolytic disease of the newborn

The changing management of haemolytic disease of the newborn is reviewed

Évaluation de la détermination du statut Rhésus-D fœtal sur plasma maternel par la technique d’hemi-nested PCR

AIMS

The aim of our study was to evaluate the possibility of identifying the fetal RhD status in maternal plasma using conventional hemi nested PCR analysis.

SUBJECTS AND METHODS

After informed written consent, 20 mL of peripheral blood were collected in 99 D-negative pregnant women either at an amniocentesis for prenatal diagnosis or at a prenatal checkup. Fetal DNA extracted from 400 microL of maternal plasma was analyzed by two different operators with a hemi-nested PCR extending an area of the RhD gene exon 10. The results were compared to the fetal RhD status obtained by PCR amniotic fluid analysis or blood analysis of newborns after delivery. The influence of mother's and baby's phenotype were also studied.

RESULTS

Among the 99 D-negative pregnant women, all Caucasian, 47 were in their second trimester and 52 in their third trimester (mean: 27.20 weeks of gestation +/-8.25). Sixty-nine fetuses were D-positive and thirty D-negative. The sensitivity and specificity of our technique were respectively 100% and 86.7% and 15% of discordant results were observed between the two operators. Four false positives were observed. According to maternal phenotype, a fetal unexpressed RHD gene was suspected in only one case because of a particular fetal phenotype (ddCcEe).

CONCLUSION

A conventional hemi nested PCR analysis of maternal plasma could be used for accurate fetal RhD status. However this procedure is difficult to apply for routine analysis because of the importance of anti-contamination measures required to obtain good results. Real time quantitative PCR analysis on fetal DNA is more suitable. Whatever the operating procedure used, polymorphism of RhD gene may follow in either false negative from presence of rearranged gene or false positive from occasional presence of a non functional RHD gene.

Results of diagnostic accuracy studies are not always validated

BACKGROUND AND OBJECTIVE

Internal validation of a diagnostic test estimates the degree of random error, using the original data of a diagnostic accuracy study. External validation requires a new study in an independent but similar population. Here we describe whether diagnostic research is validated, which technique is used, and to what extent the validation study results differ from the original.

STUDY DESIGN AND SETTING

All original diagnostic accuracy studies published in 1993 in a predefined set of journals were selected. Validation of these studies was assessed in the original article and in articles published within a period of 10 years, through a literature search and contacting the authors.

RESULTS

None of the original studies reported any form of validation. Validation studies published later could be identified for 7 of the 11 original studies. Test characteristics were difficult to compare. Despite what was generally believed, not every validation study showed results inferior to the original. We found more studies that evaluated the test in a different population than in a similar one.

CONCLUSION

Not every diagnostic accuracy study is validated. Diagnostic tests are more often repeated in different populations.

High-throughput molecular profiling of blood donors for minor red blood cell and platelet antigens

BACKGROUND

ABO and D phenotyping of both blood donors and patients receiving transfusions is routinely performed by blood banks to ensure compatibility. These analyses are performed by antibody-based agglutination assays. Blood is not tested for minor blood group antigens on a regular basis, however, because of cost and time constraints. This can result in alloimmunization of the patient against one to several minor antigens and may complicate future transfusions.

STUDY DESIGN AND METHODS

To address this problem, an assay has been generated on the GenomeLab SNPstream genotyping system to test simultaneously polymorphisms linked to 22 different blood antigens with donor's DNA isolated from minute amounts of white blood cells.

RESULTS

The results showed that both the error rate of the assay, as measured by the strand concordance rate, and the no-call rate were very low (0.1%). The concordance rate with the actual red blood cell (RBC) and platelet (PLT) serology data varied from 97 to 100 percent. Experimental or database errors as well as rare polymorphisms contributing to antigen conformation could explain the observed differences. These rates, however, are well above requirements because phenotyping and cross-matching will always be performed before transfusion.

CONCLUSION

Molecular profiling of blood donors for minor RBC and PLT antigens will give blood banks instant access to many different matched donors through the setup of a centralized data storage system.

Rh proteins: Key structural and functional components of the red cell membrane

Rh (Rhesus) proteins (D, CcEe) are expressed in red cells (RBC) in association with other membrane proteins (RhAG, LW, CD47 and GPB). By interacting with the spectrin-based skeleton through protein 4.2 and ankyrin, the Rh complex contributes to the maintenance of the mechanical properties of the erythrocyte membrane. The RH system is one of the most immunogenic and polymorphic human blood group system. Molecular basis of most Rh phenotypes, including the Rh(null) phenotype associated with hemolytic anemia, have been determined. The demonstration that the RHD-positive locus is composed of the RHD and RHCE genes, whereas the RHD gene is deleted in most RhD-negative individuals, allowed fetal RhD genotyping by non-invasive PCR assays for antenatal diagnosis of pregnancy at risk for Rh hemolytic disease of the newborn. In mammals, the Rh protein family includes two non-erythroid members, RhBG and RhCG, mainly expressed in liver and kidney, two organs specialized in ammonia genesis and excretion. Functional analyses in heterologous systems revealed that RhAG, RhBG and RhCG can mediate ammonium (NH(3) and/or NH(4)(+)) transport across the cell membrane and might represent mammalian specific ammonium transporters. Furthermore, recent studies performed in human and murine red blood cells (RBC) indicate that RhAG facilitates CH(3)NH(2)/NH(3) movement across the membrane and represents a potential example of gas channel. The crystallographic structure of the bacterial ammonia channel AmtB and functional studies showing that AmtB conducts NH(3) into reconstituted vesicles is fully consistent with these latter studies. In RBCs, RhAG may transport NH(3) to detoxifying organs like kidney and liver and with non-erythroid tissues orthologs may contribute to regulation of the acid-base balance.