Risks of red blood cell alloimmunization in transfusion-dependent β-thalassemia in Oman: a 25-year experience of a university tertiary care reference center and a literature review

Alloimmunization in β-Thalassemia and Sickle Cell Disease in Middle Eastern Countries: A Systemic Review

Sickle cell disease and β-thalassemia are important health problems in Middle Eastern countries. Transfusion is the cornerstone of the management in these disorders, and red blood cell alloimmunization is among the well-recognized adverse effects associated with it. We reviewed the literature on published studies on alloimmunization prevalence, its associated risk factors, and transfusion policies employed in these countries. Our review included 39 studies on thalassemia (including 9005 patients), and 19 on sickle cell disease (including 3867 patients). The mean alloimmunization prevalence rate in thalassemia was 13.0% (95% CI: 10.0-15.0%), while that in sickle cell disease was 14.0% (95% CI: 10.0 - 19.0%). The distribution of the prevalence rates showed considerable heterogeneity in both diseases. The most frequent alloantibodies detected were anti-K (25.9%), Anti-E (21.8%), and Anti-D (9.2%), with Rhesus and K antibodies comprising 74.2% of all antibodies detected. Some risk factors were significant in several studies, including older age, female sex, older age at first transfusion, number of transfused units, and splenectomy. The prevalence of alloimmunization was significantly higher in retrospective studies compared to cross-sectional ones, in both thalassemia and sickle cell disease (P = 0.04 in each). This review reaffirmed the need to provide ABO+Rhesus + K matched blood to hemoglobinopathy patients in the Middle East, and the need for more research on Rhesus variants in this part of the world.

Prevalence of Alloimmunization Events in Thalassemia Patients With Repeated Transfusions in the Rhesus Blood Group System: A Systematic Review and Meta Analysis

Background

Alloimmunization presents a significant challenge for patients with β-thalassemia major who depend on regular transfusion therapy. This systematic review and meta-analysis aimed to evaluate the frequency of alloimmunization within the Rhesus blood group system and identify the most prevalent alloantibodies.

Methods

A comprehensive search across multiple databases was conducted to locate epidemiological studies reporting alloimmunization in thalassemia patients undergoing repeated transfusions, specifically focusing on Rhesus antibodies. Statistical analyses were performed using R software, and heterogeneity was assessed using I2 statistics.

Results

This review included 20 studies with a total of 4,650 patients. The overall prevalence of alloimmunization was 5.4% (95% confidence interval (CI): 3.1-9.3%) across all ages, with a prevalence of 9.1% (95% CI: 5.3-15.2%) in children and 25% (95% CI: 12.7-41.2%) in adults. The pooled overall prevalence was 6.6% (95% CI: 4.2-10.2%). Among the 488 alloimmunized patients, 310 developed Rhesus-specific antibodies, with anti-E (34.58%) and anti-D (13.69%) being the most frequent.

Conclusions

This study underscores the substantial prevalence of Rhesus antibodies among alloimmunized thalassemia patients. Implementing extended phenotype matching for transfusions could significantly reduce the risk of alloantibody formation in this population. Future analyses should explore factors influencing alloimmunization rates, such as ethnic diversity, matching protocols, and age-related variations, to inform clinical practice better.

Human leukocyte antigen immunization in transfusion-dependent Moroccan patients with beta-thalassemia major: prevalence and risk factors

INTRODUCTION

Beta-thalassemia major patients need a regular blood transfusion to have an initial normal growth. However, these patients have an increased risk of developing alloantibodies. Our main goal was to study HLA alloimmunization in Moroccan Beta-thalassemia patients by confronting it with transfusion and demographic criteria, exploring the involvement of HLA typing profile in the development of HLA antibodies and in turn determining risk factors for their development.

METHODS

The study consisted of 53 Moroccan pediatric patients with Beta-thalassemia major. Screening for HLA alloantibodies was performed using Luminex technology Whereas HLA genotyping was done with sequence-specific primers (PCR-SSP).

RESULTS

In this study, 50.9% of patients have been identified as positive for HLA antibodies, with 59.3% having both HLA Class I and Class II antibodies. A significant increase frequency of DRB1*11 allele was revealed in non-immunized patients (34.6% vs. 0%, p = 0.001). Our results also revealed that the majority of our HLA immunized patients were women (72.4% vs. 27.6%, p = 0.001), and transfused with more than 300 units of RBC units (66.7% vs. 33.3%, p = 0.02). There were statistically significant differences when comparing these frequencies.

CONCLUSIONS

This paper revealed that the transfusion dependent Beta-thalassemia major patients are exposed to risk of developing HLA antibodies following transfusions with leukoreduced RBC units. The HLA DRB1*11 was a protective factor against HLA alloimmunization in our beta-thalassemia major patients.

Red blood cell alloimmunization among transfusion-dependent thalassemia major patients in Northeastern Iran

BACKGROUND

Thalassemia is one of the most common congenital hemoglobinopathies globally. Regular red blood cell (RBC) transfusion is of paramount importance in the treatment of thalassemia patients. However, this practice increases the risk of alloimmunization. This study was performed to determine the prevalence of RBC antibodies among multiple-transfused thalassemic patients in southern Khorasan, the eastern side of Iran.

METHODS

For the purpose of screening unexpected antibodies, blood samples of 68 β-thalassemia major patients were investigated. After determining positive cases through screening phase, the process of antibody identification was carried out using reagent cells.

RESULTS

The overall rate of alloimmunization was 2.9%, and the most frequent clinically important alloantibodies were anti-Kell and anti-Rh systems. Anti-K was detected in one of the patients. Furthermore, the simultaneous occurrence of anti-E and anti-C was seen in another study subject.

CONCLUSION

A number of factors might have contributed to the low alloimmunization rate detected in this study, including the homogeneity of the population in South Khorasan, well-matched donors for those patients, first transfusion at an early age, and the use of leukodepleted blood.

Characterization of Blood Group Variants in an Omani Population by Comparison of Whole Genome Sequencing and Serology

Although blood group variation was first described over a century ago, our understanding of the genetic variation affecting antigenic expression on the red blood cell surface in many populations is lacking. This deficit limits the ability to accurately type patients, especially as serological testing is not available for all described blood groups, and targeted genotyping panels may lack rare or population-specific variants. Here, we perform serological assays across 24 antigens and whole genome sequencing on 100 Omanis, a population underrepresented in genomic databases. We inferred blood group phenotypes using the most commonly typed genetic variants. The comparison of serological to inferred phenotypes resulted in an average concordance of 96.9%. Among the 22 discordances, we identify seven known variants in four blood groups that, to our knowledge, have not been previously reported in Omanis. Incorporating these variants for phenotype inference, concordance increases to 98.8%. Additionally, we describe five candidate variants in the Lewis, Lutheran, MNS, and P1 blood groups that may affect antigenic expression, although further functional confirmation is required. Notably, we identify several blood group alleles most common in African populations, likely introduced to Oman by gene flow over the last thousand years. These findings highlight the need to evaluate individual populations and their population history when considering variants to include in genotype panels for blood group typing. This research will inform future work in blood banks and transfusion services.

Red Blood Cell Alloimmunization in Pregnancy: A Review of the Pathophysiology, Prevalence, and Risk Factors

This review paper provides an overview of the risk factors and laboratory testing for red blood cell (RBC) alloimmunization in pregnancy. RBC alloimmunization is a significant medical issue that can cause haemolytic disease of the fetus and newborn (HDFN), leading to neonatal morbidity and mortality. Current HDFN prophylaxis targets only Rhesus D (RhD) alloimmunization, with no effective measures to prevent alloimmunization to other RBC antigen groups. Several factors can increase the risk of developing RBC alloimmunization during pregnancy, including fetomaternal haemorrhage, RBC and maternal genetic status, and previous transfusions. Identifying these risk factors is essential to execute the appropriate management strategies to minimize the risk of HDFN. The review also discusses the laboratory methods and overview of pregnancy management. The paper highlights the importance of identifying and managing the risk factors for RBC alloimmunization in pregnancy to minimize the risk of HDFN and improve neonatal outcomes.

Characteristics of unexpected antibodies in patients with blood disorders: Evidence in Vietnam

BACKGROUND

In Vietnam, a lack of evidence about the unexpected antibodies hinders the capabilities to prepare the necessary resources and personnel for treating patients with blood disorders. This study aimed to measure the rates of different unexpected antibodies in patients having blood orders in Vietnam.

STUDY DESIGN AND METHODS

A cross-sectional study was conducted at the National Institute of Hematology - Blood Transfusion, Vietnam on 5608 patients with blood disorders. Information was obtained from the medical records, blood transfusion forms, screening test forms.

RESULTS

The prevalence rate of unexpected antibodies in patients with haematological disorders was 9.3%. The most prevalent occurrence was the presence of an atypical antibody type, accounting for 61% of patients. The co-occurrence of this atypical antibody type and other types of antibodies was also observed, with the respective occurrence rates of 23.9%, 10.1%, 3.8%, and 1.2% for the combination of two, three, four, and five unexpected antibody types. The presence of one type of unexpected antibody was predominant, namely anti-E, accounting for the highest proportion (32.9%), followed by anti-Mia (18.4%). Among the 125 patients, the most frequently observed combination of abnormal antibodies was anti-E with anti-c (14.3%) and anti-E with anti-Mia (3.4%). Among the cohort of 53 patients exhibiting three types of unexpected antibodies, the most prevalent combination observed was anti-c, anti-E, and anti-Mia (5.7%).

CONCLUSION

This study revealed a prevalence rate of 9.3% in the presence of unexpected antibodies in patients with blood disorders. The occurrence of individual unexpected antibodies surpasses that of coordinated antibodies.

Red blood cell alloimmunization in blood transfusion-dependent β thalassemia major patients in Sana'a City-Yemen

The development of erythrocyte alloantibodies complicates transfusion therapy in β thalassemia major patients. These antibodies increase the need for blood and intensify transfusion complications. Data on erythrocyte alloimmunization is scarce in Yemeni thalassemia patients. We studied the frequency of alloimmunization in multitransfused β-thalassemia major patients and investigated risk factors that affect antibody formation. Blood samples were taken from 100 β thalassemia major patients who received multitransfused leukodepleted packed red-blood cells. Antibody screening and identification were performed by indirect antiglobulin test using the gel column technique. All patients were tested for autoantibodies using autocontrol and direct antiglobulin test. No adsorption test was done as no autoantibodies were detected in any patient. In our study of 100 β-thalassemia patients, 50 were male and 50 were female with ages ranging from 1 to 30 years. Alloantibodies were present in 6% of patients, while no autoantibodies were detected. Of the 17 alloantibodies identified, the majority were directed against Kell (41.2%) and Rh (29.4%) blood groups. Alloimmunization was significantly associated with age group and sex (p = 0.013, p = 0.030), respectively in β thalassemia major patients. The development of alloantibodies was not significantly associated with duration, total number of transfusions and splenectomy (P = 0.445, P = 0.125, P = 0.647). No autoantibodies found in patients with β thalassemia major. The study found low rates of erythrocyte alloimmunization in multitransfused β-thalassemia major patients, but significant alloantibodies were produced primarily from Kell and Rh blood groups, suggesting the need for providing phenotypically matched cells for selective antigens to improve transfusion efficiency.

Study of the Frequency and Specificity of Red Cell Antibodies in Patients with Hemoglobinopathies

Patients with thalassemia and sickle cell disease (SCD) require blood transfusions as part of their supportive care. However, one of the most serious side effects of this treatment is the risk of red cell alloimmunization. The goal of this study was to assess the prevalence and Specificity of red cell alloimmunization in Egyptian thalassemia and sickle cell anaemia patients. This study included 200 multi transfused Egyptian patients, one hundred and forty patients with transfusion dependent thalassaemia and sixty patients with sickle cell anaemia, who were attending the Paediatric Children Hospital-Cairo University at the period from March 2019 to October 2019. Alloantibody identification was made by Diamed- ID microtyping system. In the studied groups both thalassemia and sickle patients, the prevalence of alloimmunization was 22/200 (11%) patients. The two most often alloantibodies were, antibodies against Kell antigen (37%) and against E antigen (30%). The prevalence of alloimmunization was more in females in comparison to males, but it did not reach statistical significance and patients with thalassemia major had higher alloimmunization rates than other studied groups but was not statistically significant. In the D negative patients in the research group, alloimmunization demonstrated a statistically significant difference (p = 0.01). Age, gender, age of transfusion onset and splenectomy were not contributing factors to the antibody presence in the group of patients being investigated. Before receiving blood transfusions, extended red blood cell phenotyping should be thought of as a crucial procedure for hemoglobinopathies patients who would likely have several transfusions. It is advised that haemoglobinopathies patients in Egypt be checked through phenotyping of RBC units for Kell and all Rh antigens to be phenotyped before starting transfusion in these patients which is also standard of care for these patients presently.

Role of Hemin in the Immune Response of T Follicular Helper Lymphocytes Expressing T-Cell Immunoreceptor with Immunoglobulin and Immunoreceptor Tyrosine-Based Inhibitory Domains, Programmed Cell Death-1, and Interleukin-21 in Allo-Auto Positive and Negative Thalassemia

Introduction

Repeated transfusions in thalassemia patients can cause several complications, including alloimmunization and autoimmunization.

Purpose

This study compares the immune response of T follicular helper (Tfh) lymphocytes expressing T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory domains (TIGIT), programmed cell death-1 (PD-1), and interleukin-21 (IL-21) between patients with allo-auto positive and negative thalassemia before and after hemin administration.

Materials and Methods

This study used a quasi-experimental pre- and post-test design and was performed between April and November 2021 at the Dr. Soetomo General Academic Hospital in Surabaya, Indonesia. It enrolled 29 patients with allo-auto positive thalassemia and 28 with allo-auto negative, and 9 mL of whole blood (WB) was drawn from each patient. Hemin solution (20 µM) was added to 5 mL of WB, incubated for two hours, processed into peripheral blood mononuclear cells (PBMCs) in RPMI media, and cultured with 5% CO2 for three days. The 4 mL WB sample was also processed into PBMCs. PBMC cells cultured and without cultured were examined by flow cytometry using a BD FACSCalibur after surface and intracellular staining. Differences in Tfh cells expressing TIGIT, PD-1, and IL-21 between thalassemia groups before and after hemin administration were compared using independent t-tests or Mann-Whitney U-tests (p < 0.05).

Results

Tfh cell expression did not differ between groups before hemin administration and increased after hemin administration. The increase in Tfh cell expression was higher in the allo-auto positive group. TIGIT and PD-1 expression in Tfh cells did not differ between groups, but TIGIT decreased after hemin administration in contrast to PD-1 result. IL-21 expression in Tfh cells did not differ between groups and did not change after hemin administration.

Conclusion

Hemin affected the expression of Tfh cells in both group thalassemia, but there was no difference of Tfh cell expression between the groups.

Impact of Hemin on Interleukin-21 Levels and Plasma Cells in Transfusion-Dependent Thalassemia with Positive and Negative Allo-Autoantibody

Introduction

Antibody formation in transfusion-dependent thalassemia is associated with chronic hemolysis and repeated transfusions. Hemolysis produces heme, which mediates B-cell differentiation into plasma cells and produces antibodies influenced by interleukin-21 (IL-21).

Objective

This study aimed to compare IL-21 levels, plasma cell percentage, and red blood cell antibodies between positive and negative allo-autoantibody thalassemia before and after hemin administration.

Materials and Methods

This research employed a quasi-experimental nonequivalent control group pre-test and post-test design performed from April to November 2021 at Soetomo Academic Hospital in Surabaya, Indonesia. Heparinized blood samples of 5 mL and 4 mL and EDTA blood samples of 3 mL were taken from positive (29 patients) and negative (28 patients) allo-autoantibody thalassemia participants. Hemin 20 µM was added to 5 mL of heparinized blood, incubated for 2 hours, prepared into peripheral blood mononuclear cells (PBMCs), and cultured for 3 days. The percentage of plasma cells (CD38+CD184+) of cultured and uncultured PBMCs was measured by BD FACSCalibur Flow Cytometer. IL-21 levels of plasma and supernatants were measured with Sandwich Enzyme-Linked Immunosorbent Assay by Elabscience. Red blood cell antibodies were detected by QWALYS 3 E.M. Technology. Autoantibodies were determined by the Grifols gel tube method.

Results

IL-21 levels were significantly different in the positive and negative allo-autoantibody thalassemia groups after hemin administration. The percentage of plasma cells in the positive allo-autoantibody group increased significantly after the administration of hemin. The percentage of plasma cells between thalassemia groups was not significantly different before the hemin administration but increased significantly after it. Red blood cell antibodies after the administration of hemin were significantly different in the negative allo-autoantibody group but not significantly different in the positive allo-autoantibody group.

Conclusion

Hemin administration affected IL-21 levels, plasma cell percentage, and antibody formation in positive and negative allo-auto antibody thalassemia.

Red blood cell alloimmunization and other transfusion-related complications in patients with transfusion-dependent thalassemia: A multi-center study in Thailand

BACKGROUND

Thalassemia is a common genetic disease in Southeast Asia. Red blood cell (RBC) transfusion is an essential treatment for severe forms of thalassemia. We performed a study to demonstrate RBC alloimmunization and other transfusion-related complications in patients with transfusion-dependent thalassemia (TDT).

STUDY DESIGN AND METHODS

A multi-center web-based registry of TDT was conducted in eight medical centers across Thailand. Thalassemia information, transfusion therapy, and transfusion-related complications were collected. Factors associated with each complication were demonstrated using the logistic regression analysis.

RESULTS

Of 1000 patients recruited for the study, 449 were males (44.9%). The mean age was 23.9 ± 15.4 years. The majority of patients, 738 (73.8%) had hemoglobin E/beta-thalassemia. In the study, 421 transfusion-related complications were reported from 357 patients (35.7%). Alloimmunization was the most common complication which was found in 156 patients (15.6%) with 284 positive antibody tests. The most frequent antibodies against RBC were anti-E (80/284, 28.2%) followed by anti-Mia (45/284, 15.8%) and anti-c (32/284, 11.3%). Age ≥3 years at initial blood transfusion, splenomegaly, higher frequencies, and volumes of transfusion were significant factors associated with alloimmunization. None of the patients had to terminate blood transfusion due to multiple alloantibodies. Other commonly seen complications were allergic reactions (130, 13.0%), autoimmune hemolytic anemia (70, 7.0%) and febrile non-hemolytic transfusion reaction (54, 5.4%).

CONCLUSIONS

Transfusion-related complications, especially alloimmunization, were common among Thai patients with TDT. Extended RBC antigen-matching for the Rh system and Mia should be implemented to prevent the development of alloantibodies in multi-transfused patients.

COVID-19 Pandemic and Thalassemia Major Patients: Transfusion Practice and Treatment Assessment

BACKGROUND

When the COVID-19 epidemic occurred for the first time in December 2019, the governments worldwide took some restriction measures for slowing the spread of novel coronavirus. Eventually, there was a considerable decrease in volunteer blood donations. Regular transfusions and follow-up of patients with thalassemia major (TM) should be maintained during this period. It is possible that the treatment of the patients with TM may hinder due to the difficulty of reaching the treatment center and the difficulty of blood supply. Thus, in this study, we aimed to investigate whether there were any differences in the follow-up and treatment of the patients with TM during the outbreak.

MATERIALS AND METHODS

Sixty-one patients with TM who were followed up in our center without COVID-19 contact history and symptoms were included in this study. The demographic features and red blood cell volume per kilogram they received, pretransfusion hemoglobin, serum ferritin (SF) level, biochemical parameters, and transfusion interval were recorded. The difference between the arithmetic mean of the data before and during the pandemic was evaluated.

RESULTS

In this study, 61 patients with TM (32 males/29 females, mean age 13.9±6.8 y) were evaluated. The mean pretransfusion hemoglobin value was 9.14±0.77 g/dL and 8.87± 0.80 g/dL before and during the pandemic, respectively (P=0.023). There was no difference between before and during the pandemic concerning transfusion interval and transfusion volume. However, SF levels increased above 1000 ng/mL in 16.6% of patients.

CONCLUSION

Although blood donation decreased significantly during the pandemic, it was observed in this study that the blood needs of patients with TM could be provided. The results of the SF level showed that the management of chelation therapy should be more meticulous. However, we should be ready for the challenges in the transfusion practice of patients with TM due to fluctuations in the COVID-19 pandemic.

Molecular blood group screening in Omani blood donors

BACKGROUND AND OBJECTIVES

Blood group genotyping has been used in different populations. This study aims at evaluating the genotypes of common blood group antigens in the Omani blood donors and to assess the concordance rate with obtained phenotypes.

MATERIAL AND METHODS

Blood samples from 180 Omani donors were evaluated. Samples were typed by serological methods for the five blood group systems MNS, RH (RHD/RHCE), KEL, FY and JK. Samples were genotyped using RBC-FluoGene vERYfy eXtend kit (inno-train©). Predicted phenotypic variants for 70 red blood cell antigens among the MNS, RH (RHD/RHCE), KEL, FY, JK, DO, LU, YT, DI, VEL, CO and KN blood group systems were assessed.

RESULTS

Simultaneous phenotype and genotype results were available in 130 subjects. Concordance rate was >95% in all blood group systems with exception of Fy(b+) (87%). Homozygous GATA-1 mutation leading to erythroid silencing FY*02N.01 (resulting in the Fy(b-)^ES phenotype) was detected in 81/112 (72%) of genotyped samples. In addition, discrepant Fy^b phenotype/genotype result was obtained in 14/112 samples; 13 of which has a heterozygous GATA-1 mutation and one sample with a wild GATA genotype. D and partial e c.733C>G variants expressing the V+VS+ phenotype were found in 22/121 (18.2%) and 14/120 (11.7%) of the samples, respectively. Di(a-b+), Js(a-b+), Yt(a+b-) and Kn(a+b-) genotype frequencies were 99.4%, 95.8%, 91.9% and 97.7%, respectively.

CONCLUSION

In conclusion, we report a high frequency of FY*02N.01 allele due to homozygous c.-67T>C GATA-1 single-nucleotide variation. This is the first study reporting the detailed distribution of common and rare red cell genotypes in Omani blood donors.

High B-cell activating factor levels in multi-transfused thalassemia patients

OBJECTIVES

To assess the associations between B-cell activating factor (BAFF) and alloimmunisation in multi-transfused thalassemia.

BACKGROUND

Red blood cell (RBC) alloimmunisation is a complication of multi-transfused thalassemia. BAFF is promoting B cells that produce alloantibodies.

METHODS/MATERIALS

Multi-transfused thalassemia, 15 years or older, were recruited in the cohort study. Alloantibodies and BAFF levels were analysed.

RESULTS

Of 114 patients, the overall prevalence of RBC alloimmunisation was 29.8%. The most common alloantibodies were anti-E, anti-Mi^a and anti-c. BAFF levels were different among the three groups; the patients with baseline alloantibodies (median ± interquartile range 1251 ± 474 pg/ml), without alloantibodies (1098 ± 453) and healthy controls (719 ± 306), p < 0.001. The BAFF level was elevated in the >25 years old patients (vs. the <25, p = 0.011) and the buffy-coat-reduced blood recipients (vs. the pre-storage leukocyte-depletion, p = 0.005). Absolute lymphocyte count was higher in the patients without baseline alloantibodies (vs. with baseline alloantibodies, p = 0.049) and the splenectomised patients (vs. the non-splenectomised patients, p < 0.001). Of the 72 patients without baseline antibodies, four who developed new antibodies showed no statistically different BAFF levels compared with those without new antibodies after 40-month follow-up (1296 ± 734 vs. 1062 ± 460, p = 0.491). In multivariate analysis, BAFF to absolute lymphocyte ratio was independently associated with RBC alloimmunisation (odds ratio 3.07, 95% confidence interval 1.124-8.369, p = 0.029).

CONCLUSION

B-cell activating factor (BAFF) levels were elevated in multi-transfused thalassemia and the BAFF to absolute lymphocyte ratio was associated with red blood cell (RBC) alloimmunisation.

Non-transfusion dependent thalassemia is independently associated with higher alloimmunization risk than transfusion dependent thalassemia and would benefit the most from extended red cell antigen-matching

BACKGROUND

Alloimmunization prevalence is conventionally used to identify RBCs alloimmunization risk factors among thalassemia patients, but it may be confounded by differences in transfusion exposure especially between non-transfusion dependent thalassemia (NTDT) and transfusion dependent thalassemia (TDT) patients. To better identify thalassemia patients with high alloimmunization risks, we used cumulative incidence of first alloimmunization as a function of RBCs transfused to compare alloimmunization risks between TDT and NTDT and to evaluate other risk factors. We also proposed practical strategies to prevent alloimmunization in thalassemia.

STUDY DESIGN AND METHODS

Adult TDT and NTDT patients who had received ≥2 transfusions and no alloimmunization before their first transfusion were included. Alloimmunization was defined as the development of clinically significant alloantibodies. We estimated the first alloimmunization incidence from transfusion by Kaplan-Meier analysis with the horizontal axis expressed as cumulative non-antigen-matched RBC units transfused. We compared this incidence between TDT and NTDT, and analyzed for other alloimmunization risk factors and the alloantibody specificities/frequencies.

RESULTS

The alloimmunization prevalence was similar between TDT and NTDT (27% vs. 30% respectively, p = .726). However, for the same transfusion exposure, NTDT had higher alloimmunization incidence than TDT (hazard ratio 8.59, 95% confidence interval [2.25-32.74], p = .002), independent of age at first transfusion and last follow-up, gender, and splenectomy. Anti-E, anti-c, anti-Mi^a , and anti-Jk^a were most frequent.

DISCUSSION

NTDT has the highest alloimmunization risk and would benefit the most from extended RBC antigen-matching, especially C, c, E, and e. Other blood group antigen-matching should be guided by the patient/donor disparities and alloantibody frequencies in different populations.

A study of red blood cell alloimmunization and autoimmunization among 200 multitransfused Egyptian β thalassemia patients

The development of hemolytic erythrocyte alloantibodies and autoantibodies complicates transfusion therapy in thalassemia patients. These antibodies ultimately increase the need for blood and intensify transfusion complications. There is a scanty data on the frequency of RBC alloimmunization and autoimmunization in Egyptian β thalassemia patients as pretransfusion antibody screening is not routinely performed. We studied the frequency of alloimmunization and autoimmunization among 200 multiply transfused β thalassemia patients and investigated the factors that possibly affect antibody formation. Of the 200 patients in our study, 94 were males and 106 females, with the age range of 2–37 years. Alloantibodies were detected in 36 (18%) of the patients, while autoantibodies were detected in 33 (16.5%). The dominant alloantibodies were directed against Kell (33%) and Rh (24.4%) groups. Alloimmunization had a significant relationship with treatment duration and the frequency of transfusion (P = 0.007, 0.001, respectively). The presence of autoantibodies was significantly related to age (P = 0.001), total number of transfused units (P = 0.000) and splenectomy (P = 0.000). The high prevalence of alloimmunization in the study population disclosed the need for providing phenotypically matched cells for selective antigens especially for Kell and Rh subgroups to reduce risk of alloimmunization and increase the efficiency of blood transfusion.

Distribution of Red Blood Cell Alloantibodies Among Transfusion-Dependent β-Thalassemia Patients in Different Population of Iran: Effect of Ethnicity

The best approach for prevention of alloimmunization in β-thalassemia (β-thal) patients is perfect matching of all red blood cell (RBC) antigens associated with clinically significant antibodies, but this is expensive and may limit the blood supply. Knowing the most common alloantibodies in transfusion-dependent β-thal patients make it possible to establish more cost-effective matching strategies for high-risk antigens. With this in mind, we intended to determine the most common alloantibodies in different parts of Iran. A total of 480 alloimmunized β-thal major (β-TM) patients who were referred to the Tehran Adult Thalassemia Clinic in Tehran, Iran from all provinces between 2015 and 2017, were included in this study. Antibody screening was performed on the fresh serum of all patients. Subsequently, the specification of antibodies was identified using a panel of recognized blood group antigens. Anti-K was the most common alloantibody detected in β-TM patients in all regions of Iran. The prevalence of this antibody reached to 37.7% in the western area, but in southeastern region, anti-E was predominant. Interestingly, the rare alloantibody anti-Kp^a was detected with a high prevalence in the western region. The antibodies against E and D antigens were also encountered with high prevalence in most regions of the country. The present study demonstrated the distribution of alloantibodies in alloimmunized transfusion-dependent β-thal patients from diverse ethnic and racial backgrounds of the Iranian population. The results of this study can be used as a basis to establish cost-effective RBC phenotyping and matching strategies for high-risk antigens in donors and chronic transfusion recipients in different regions of Iran.

Study of Frequency and Characteristics of Red Blood Cell Alloimmunization in Thalassemic Patients: Multicenter Study from Palestine

Background. β-Thalassemia is a common inherited hemolytic disorder in Palestine. Red blood cell (RBC) transfusion is the principal treatment but it may cause RBC alloimmunization. This study was conducted to determine the prevalence and characteristics of RBC alloimmunization among thalassemic patients in northern governorates of Palestine. Methods. A prospective multicenter observational study was conducted in the thalassemia transfusion centers in the northern governorates of Palestine. The study included 215 thalassemia patients who received regular blood transfusions. Clinical and transfusion records of patients were examined. Antibody screening and identification was conducted using the microcolum gel technique. Results. Two hundred fifteen patients were included in the study. More than half (52.1%) of the patients were males. The median age of patients was 18 years (range: 12–24 years). The most frequent blood group was A (40.5%). Alloantibodies were detected in 12.6% of patients. Anti-D (33.3%), anti-K (25.9%) and anti-E (14.8%) were the most commonly isolated antibodies. There was no association between age, sex, starting age of transfusion, number of transfused units, history of splenectomy and alloimmunization. Conclusions. Anti-Rh and anti-K antibodies were common among this cohort of patients. Age, sex, starting age of transfusion, number of transfused units, and history of splenectomy could not predict the occurrence of alloimmunization.

Prevalence of Red Blood Cell Major Blood Group Antigens and Phenotypes among Omani Blood Donors

Objectives

Most literature on the frequencies of red blood cell (RBC) phenotypes are published in Europeans and Africans countries, with the frequencies in the Omani population unknown. We sought to determine the prevalence of RBC blood group phenotypes among Omani blood donors.

Methods

Blood group ABO, RhD type, and phenotyping were performed for 21 blood group antigens on enrolled blood donors. The following antigens were assessed serologically: Rh (C, c, E, e), Kell (K, k, Kp^a, Kp^b), Kidd (Jk^a, Jk^b), Duffy (Fy^a, Fy^b), Lewis (Le^a, Le^b), Lutheran (Lu^a, Lu^b), MNS (M, N, S, s), and P1.

Results

A total of 337 Omani blood donors were tested. The most common blood group was O+ (44.9%). Among the tested blood donors studied, 89.3% were RhD positive with R1r being the most common Rh phenotype. The k antigen was found at a frequency of 99.4%, while 4.5% of the blood donors studied were K+. The most common phenotype in the Duffy blood group system was Fy(a-b-), while the most common phenotypes in the Kidd and MNS blood group systems were Jk(a+b+) and M+N-S+s+ at 47.0% and 22.6%, respectively. The Le(a+) and Le(b+) antigens were found in 21.7% and 67.3% of the blood donors, respectively. One Jk(a-b-), one Le(a+b+), and two Lu(a-b-) individuals were identified.

Conclusion

This is the first study to examine the frequencies of RBC phenotypes among the Omani blood donors. The study's results show Duffy blood group frequencies that resemble what has been reported in the African population, and higher frequencies of the rare null phenotypes compared to European populations.

Amustaline-glutathione pathogen-reduced red blood cell concentrates for transfusion-dependent thalassaemia

Transfusion‐dependent thalassaemia (TDT) requires red blood cell concentrates (RBCC) to prevent complications of anaemia, but carries risk of infection. Pathogen reduction of RBCC offers potential to reduce infectious risk. We evaluated the efficacy and safety of pathogen‐reduced (PR) Amustaline‐Glutathione (A‐GSH) RBCC for TDT. Patients were randomized to a blinded 2‐period crossover treatment sequence for six transfusions over 8–10 months with Control and A‐GSH‐RBCC. The efficacy outcome utilized non‐inferiority analysis with 90% power to detect a 15% difference in transfused haemoglobin (Hb), and the safety outcome was the incidence of antibodies to A‐GSH‐PR‐RBCC. By intent to treat (80 patients), 12·5 ± 1·9 RBCC were transfused in each period. Storage durations of A‐GSH and C‐RBCC were similar (8·9 days). Mean A‐GSH‐RBCC transfused Hb (g/kg/day) was not inferior to Control (0·113 ± 0·04 vs. 0·111 ± 0·04, P = 0·373, paired t‐test). The upper bound of the one‐sided 95% confidence interval for the treatment difference from the mixed effects model was 0·005 g/kg/day, within a non‐inferiority margin of 0·017 g/kg/day. A‐GSH‐RBCC mean pre‐transfusion Hb levels declined by 6·0 g/l. No antibodies to A‐GSH‐RBCC were detected, and there were no differences in adverse events. A‐GSH‐RBCCs offer potential to reduce infectious risk in TDT with a tolerable safety profile.

Red blood cell alloimmunisation in transfusion-dependent thalassaemia: a systematic review

BACKGROUND

Chronic red blood cell transfusion is the first-line treatment for severe forms of thalassaemia. This therapy is, however, hampered by a number of adverse effects, including red blood cell alloimmunisation. The aim of this systematic review was to collect the current literature data on erythrocyte alloimmunisation.

MATERIALS AND METHODS

We performed a systematic search of the literature which identified 41 cohort studies involving 9,256 patients.

RESULTS

The prevalence of erythrocyte alloimmunisation was 11.4% (95% CI: 9.3-13.9%) with a higher rate of alloimmunisation against antigens of the Rh (52.4%) and Kell (25.6%) systems. Overall, alloantibodies against antigens belonging to the Rh and Kell systems accounted for 78% of the cases. A higher prevalence of red blood cell alloimmunisation was found in patients with thalassaemia intermedia compared to that among patients with thalassaemia major (15.5 vs 12.8%).

DISCUSSION

Matching transfusion-dependent thalassaemia patients and red blood cell units for Rh and Kell antigens should be able to reduce the risk of red blood cell alloimmunisation by about 80%.