Molecular testing in transfusion medicine

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.

Integration of red cell genotyping into the blood supply chain: a population-based study

BACKGROUND

When problems with compatibility arise, transfusion services often use time-consuming serological tests to identify antigen-negative red cell units for safe transfusion. New methods have made red cell genotyping possible for all clinically relevant blood group antigens. We did mass-scale genotyping of donor blood and provided hospitals with access to a large red cell database to meet the demand for antigen-negative red cell units beyond ABO and Rh blood typing.

METHODS

We established a red cell genotype database at the BloodCenter of Wisconsin on July 17, 2010. All self-declared African American, Asian, Hispanic, and Native American blood donors were eligible irrespective of their ABO and Rh type or history of donation. Additionally, blood donors who were groups O, A, and B, irrespective of their Rh phenotype, were eligible for inclusion only if they had a history of at least three donations in the previous 3 years, with one donation in the previous 12 months at the BloodCenter of Wisconsin. We did red cell genotyping with a nanofluidic microarray system, using 32 single nucleotide polymorphisms to predict 42 blood group antigens. An additional 14 antigens were identified via serological phenotype. We monitored the ability of the red cell genotype database to meet demand for compatible blood during 3 years. In addition to the central database at the BloodCenter of Wisconsin, we gave seven hospitals online access to a web-based antigen query portal on May 1, 2013, to help them to locate antigen-negative red cell units in their own inventories.

FINDINGS

We analysed genotype data for 43,066 blood donors. Requests were filled for 5661 (99.8%) of 5672 patient encounters in which antigen-negative red cell units were needed. Red cell genotyping met the demand for antigen-negative blood in 5339 (94.1%) of 5672 patient encounters, and the remaining 333 (5.9%) requests were filled by use of serological data. Using the 42 antigens represented in our red cell genotype database, we were able to fill 14,357 (94.8%) of 15,140 requests for antigen-negative red cell units from hospitals served by the BloodCenter of Wisconsin. In the pilot phase, the seven hospitals identified 71 units from 52 antigen-negative red cell unit requests.

INTERPRETATION

Red cell genotyping has the potential to transform the way antigen-negative red cell units are provided. An antigen query portal could reduce the need for transportation of blood and serological screening. If this wealth of genotype data can be made easily accessible online, it will help with the supply of affordable antigen-negative red cell units to ensure patient safety.

FUNDING

BloodCenter of Wisconsin Diagnostic Laboratories Strategic Initiative and the NIH Clinical Center Intramural Research Program.

Molecular typing for blood group antigens within 40 min by direct polymerase chain reaction from plasma or serum

Determining blood group antigens by serological methods may be unreliable in certain situations, such as in patients after chronic or massive transfusion. Red cell genotyping offers a complementary approach, but current methods may take much longer than conventional serological typing, limiting their utility in urgent situations. To narrow this gap, we devised a rapid method using direct polymerase chain reaction (PCR) amplification while avoiding the DNA extraction step. DNA was amplified by PCR directly from plasma or serum of blood donors followed by a melting curve analysis in a capillary rapid-cycle PCR assay. We evaluated the single nucleotide polymorphisms underlying the clinically relevant Fy^a , Fy^b , Jk^a and Jk^b antigens, with our analysis being completed within 40 min of receiving a plasma or serum sample. The positive predictive value was 100% and the negative predictive value at least 84%. Direct PCR with melting point analysis allowed faster red cell genotyping to predict blood group antigens than any previous molecular method. Our assay may be used as a screening tool with subsequent confirmatory testing, within the limitations of the false-negative rate. With fast turnaround times, the rapid-cycle PCR assay may eventually be developed and applied to red cell genotyping in the hospital setting.

Implementing mass-scale red cell genotyping at a blood center

BACKGROUND

When problems with compatibility beyond ABO and D arise, currently transfusion services search their inventories and perform time-consuming serologic testing to locate antigen-negative blood. These clinically important blood group antigens can be detected reliably by red cell genotyping, which is a technology whereby DNA-based techniques are used to evaluate gene polymorphisms that determine the expression of blood group antigens. We introduced mass-scale genotyping and measured availability of genotyped blood.

STUDY DESIGN AND METHODS

All non-Caucasian donors qualified for genotyping along with donors who had a history of repeat donation. Mass-scale red cell genotyping, performed on an electronic interfaced open array platform, was implemented to screen blood donors for 32 single-nucleotide polymorphisms that predicted 42 blood group antigens. Genotype screening results were confirmed by phenotyping, when needed for antigen-negative transfusion, before release of the red blood cell (RBC) unit.

RESULTS

Approximately 22,000 donors were red cell genotyped within 4 months and a total of 43,066 donors in 4 years. There were 463 discordances (0.52% of 89,596 genotypes with a phenotype). Among the 307 resolved discordances, approximate equal numbers represented historical serologic or genotyping discrepancies (n = 151 and n = 156, respectively). In the final year of the study, a mean of 29% of the daily inventory had a genotype.

CONCLUSIONS

Red cell genotyping of blood donors using an electronic interface created a large and stable supply of RBC units with historical genotypes. The database served the needs of antigen-negative blood requests for a large regional blood center and allowed us to abandon screening by serology.

Extended blood group molecular typing and next-generation sequencing

Several high-throughput multiplex blood group molecular typing platforms have been developed to predict blood group antigen phenotypes. These molecular systems support extended donor/patient matching by detecting commonly encountered blood group polymorphisms as well as rare alleles that determine the expression of blood group antigens. Extended molecular typing of a large number of blood donors by high-throughput platforms can increase the likelihood of identifying donor red blood cells that match those of recipients. This is especially important in the management of multiply-transfused patients who may have developed several alloantibodies. Nevertheless, current molecular techniques have limitations. For example, they detect only predefined genetic variants. In contrast, target enrichment next-generation sequencing (NGS) is an emerging technology that provides comprehensive sequence information, focusing on specified genomic regions. Target enrichment NGS is able to assess genetic variations that cannot be achieved by traditional Sanger sequencing or other genotyping platforms. Target enrichment NGS has been used to detect both known and de novo genetic polymorphisms, including single-nucleotide polymorphisms, indels (insertions/deletions), and structural variations. This review discusses the methodology, advantages, and limitations of the current blood group genotyping techniques and describes various target enrichment NGS approaches that can be used to develop an extended blood group genotyping assay system.

Prospects for the provision of genotyped blood for transfusion

Blood group genotyping is gaining widespread adoption in blood centres and transfusion services. The current interest for a blood centre is its use as a screening tool to accurately predict donor phenotypes. However, not only is blood group genotyping used to screen for uncommon and rare types on a mass-scale, it can be used to optimize the inventory of multiple antigen-negative screened units. In addition, blood group genotyping provides blood types when antisera are not available, it can predict weak and variant antigens, and can aid in the resolution of ABO discrepancies. There are quality improvement benefits in blood group genotyping because it can screen for RHD alleles in Rh-negative blood donors and can be used to confirm that donors are suitable for reagent red cell production. It is possible that blood group genotyping information may be used as a donor recruitment tool. Given that genotyping can convey much more information about the expression of some complex antigens, e.g. hrB, Uvar, and Duffy, clinical trials are probably needed to show that genotyped or 'dry matched' transfusions are superior to phenotyped blood.