Transfusing children with sickle cell disease using blood group genotyping when the pool of Black donors is limited

BACKGROUND

Red blood cell transfusion is an effective treatment for patients with sickle cell disease (SCD). Alloimmunization can occur after a single transfusion, limiting further usage of blood transfusion. It is recommended to match for the ABO, D, C, E, and K antigens to reduce risks of alloimmunization. However, availability of compatible blood units can be challenging for blood providers with a limited number of Black donors.

STUDY DESIGN AND METHODS

A prospective cohort of 205 pediatric patients with SCD was genotyped for the RH and FY genes. Transfusion and alloimmunization history were collected. Our capacity to find RhCE-matched donors was evaluated using a database of genotyped donors.

RESULTS

Nearly 9.8% of patients carried a partial D variant and 5.9% were D-. Only 45.9% of RHCE alleles were normal, with the majority of variants affecting the RH5 (e) antigen. We found an alloimmunization prevalence of 20.7% and a Rh alloimmunization prevalence of 7.1%. Since Black donors represented only 1.40% of all blood donors in our province, D- Caucasian donors were mostly used to provide phenotype matched products. Compatible blood for patients with rare Rh variants was found only in Black donors. A donor with compatible RhCE could be identified for all patients.

CONCLUSION

Although Rh-compatible donors were identified, blood units might not be available when needed and/or the extended phenotype or ABO group might not match the patient. A greater effort has to be made for the recruitment of Black donors to accommodate patients with SCD.

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.

Red blood cell antigen portrait of self-identified black donors in Quebec

OBJECTIVES

The goal of this study was to establish a red blood cell antigen portrait of self-identified Black donors for the province of Quebec, Canada.

BACKGROUND

The demand for extensively phenotyped red blood cells is on the rise. A good example is the sickle cell patient cohort. To better answer their transfusion needs, Héma-Québec put forward great efforts to increase the recruitment of donors among cultural communities.

MATERIALS AND METHODS

In October 2009, an optional question was added on the record of donation to indicate the donor's ethnicity. Self-identified Black donors were extensively phenotyped by the Immunohematology Laboratory, whereas the Research and Development team genotyped red blood cell antigens to complete the picture.

RESULTS

Approximately 1500 self-identified Black donors have donated blood at least once since the beginning of the programme. Genotyping results predicted rare phenotypes: 18 S-s- (3 U-, 15 U+(w) ), 15 Js(a+b-), 5 Hy-, 3 Jo(a-), 34 hr(B) +(w) /- and 15 hr(B)-.

CONCLUSION

These Black donors, with or without a rare phenotype, are precious to the patient cohort depending on blood transfusions and to our organisation as the blood provider for the whole province of Quebec.

Set-up and routine use of a database of 10,555 genotyped blood donors to facilitate the screening of compatible blood components for alloimmunized patients

BACKGROUND AND OBJECTIVES

Large-scale genotyping of blood donors for red blood cell and platelet antigens has been predicted to replace phenotyping assays in the screening of compatible blood components for alloimmunized patients. Although several genotyping platforms have been described, novel procedures and processes are needed to perform genotyping efficiently and to maximize its benefits for blood banks.

MATERIALS AND METHODS

Here we describe the processes and procedures developed to introduce large-scale genotyping in our routine operations.

RESULTS

Preliminary cost-benefit analysis indicated that genotyping must target frequent blood donors (> 3 donations/year) to be efficiently used. A custom-designed computer application was developed to manage the whole project. It selects frequent donors among recent donations, prints coded labels to identify blood samples sent to the external genotyping laboratory, and stores genotyping results. It can search for donors compatible for any combination of the 22 genotyped antigens as well as consult the current inventory for the presence of the corresponding blood components. The phenotype of recovered components is confirmed by standard serology techniques prior to shipment to hospitals.

CONCLUSION

Since October 2007, 10 555 blood donors have been genotyped. The database is used on a regular basis to find compatible blood components with a genotype-phenotype concordance of 99.6%.

A new DEL variant caused by exon 8 deletion

BACKGROUND

A 28-year-old woman of Lebanese origin experienced two stillbirths. At the time, serology typed her red blood cells as being group A D- and found an anti-D in her serum sample. Molecular biology analysis, however, showed that she was in fact RHD+.

STUDY DESIGN AND METHODS

To better characterize this case, a full investigation including family members was undertaken. Classical serology techniques and DNA and RNA analysis were performed whenever possible.

RESULTS

Serology results showed that the patient's father and two brothers were D-. RHD genotyping demonstrated that her two brothers were indeed RHD+. Polymerase chain reaction (PCR) amplification was performed on each RHD 10 exons. Exon 8 did not amplify for the patient, her father, and her two brothers. Her mother and sister had exon 8. Messenger RNA analysis showed five RHD transcripts. The longest transcript was missing exon 8 but had a part of intron 7 inserted instead. Genomic DNA sequencing revealed a 995-bp deletion including part of intron 7, exon 8, and intron 8. This mutation, RHD(delEx8), was found to express a DEL in adsorption-elution. To facilitate the screening of this new DEL allele, a simple PCR-based assay was designed.

CONCLUSION

This novel allele represents the first observation of a large deletion at the genomic level within the RHD gene in Caucasian persons.