Risk of alloimmunization and delayed hemolytic transfusion reactions in patients with sickle cell disease

Blood transfusion is an integral part of the supportive care of patients with sickle cell diseases. The hazards of red blood cell alloimmunization and delayed hemolytic transfusion reactions (DHTRs) complicate the treatment of patients with sickle cell diseases, particularly since such reactions may be misinterpreted as a pain crisis, and, as a result, specific transfusion serologic studies may not be performed. The frequency of alloimmunization in this population has been the subject of several reports; however, the frequency of DHTRs is unknown. To determine the frequency of this event, we retrospectively reviewed the medical and transfusion service records of all adult patients with sickle cell diseases transfused during the six-year period from January 1980 to December 1985. Seventy-three adult patients with sickle cell diseases received transfusions. The prevalence of recognized DHTR was three (4%) of 73. Red blood cell alloimmunization was seen in 22 (30%) of 73 of the patients. The calculated risk of alloimmunization was 3.1% per unit of blood. These observations suggest that alloimmunization and clinically apparent DHTRs occur more frequently in patients with sickle cell diseases and support pretransfusion testing for at least Rh and Kell red blood cell antigens in patients who are at high risk of such events (patients who have formed an alloantibody or who are being enrolled in a transfusion program).     

Transfusion and alloimmunization in sickle cell disease. The Cooperative Study of Sickle Cell Disease

In 1,814 patients with sickle cell disease who had been transfused, the overall rate of alloimmunization to erythrocyte antigens was 18.6%. The rate of alloimmunization in this group appears to be an explicit function of the number of transfusions received because it increases exponentially with increasing numbers of transfusions. Alloimmunization usually occurred with less than 15 transfusions, although the rate of alloimmunization continued to increase when more transfusions were given. The rate of alloimmunization was less in patients with hemoglobin SC disease and sickle-beta+ thalassemia because these patients had received fewer transfusions. Children less than 10 years old had a slightly lower rate of alloimmunization than patients in other age groups even after correction for the number of transfusions given. Women were more frequently alloimmunized than men; this was largely due to the fact that women received more transfusions than men, but in the age group 16 to 20 years the increase may have been due in part to alloimmunization owing to pregnancy. Forty-five percent of those alloimmunized made antibodies of only one specificity; 17% made four or more antibodies reacting with different antigens. Antibodies to the C and E antigens of the Rh group, the Kell antigen, and the Lewis antigens were most commonly made. These findings may be important in formulating a rational transfusion policy in sickle cell disease.     

A simple,practical model for reducing alloimmunization in patients with sickle cell disease

Patients with sickle cell disease (SCD) form immune alloantibodies more frequently than other transfused populations because red cells (RBCs) from white donors (with a higher incidence of certain Rh, Duffy, Kell, and Kidd blood group antigens) are transfused to black patients often lacking these antigens. We propose a model to reduce alloimmunization in patients with SCD by providing them with blood from only black random donors. Rationale is shown by examining calculations based on the phenotype E–, C–, Fy(a–), K–, and Jk(b–). There is a 7% probability that this phenotype belongs to a white donor, while there is a 93% probability that this phenotype belongs to a black donor. The probability of selecting blood from a black donor identical with the above phenotype for black recipients from an all black population and from a typical urban blood inventory population (90% white, 10% black) is 1/4 and 1/33, respectively. Therefore, an 8-fold greater chance of selecting antigen non-identical blood occurs if blood is obtained from a typical urban donor population as compared to a black population. Based on these calculations, alloimmunization can be reduced prospectively in patients with SCD by meeting their transfusion requirements with blood selected from random black blood donors.     

Predictors of Red Cell Alloimmunization in Kurdish Multi Transfused Patients with Hemoglobinopathies in Iraq

Abstract

Hemoglobinopathies are significant health problems in Iraq, including its Northern Kurdistan region. One of the essential components of management of these disorders is regular lifelong blood transfusions. The latter is associated with several complications including red cell alloimmunization. No study has looked at the frequency of alloimmunization and its associations in the country. To address the latter issue, 401 multi transfused patients [311 with β-thalassemia (β-thal) syndrome and 90 with sickle cell disease], registered at a large thalassemia care center in Iraqi Kurdistan had their records reviewed, and their sera tested for atypical antibodies using screening and extended red cell panels. Red cell alloimmunization was detected in 18 patients (4.5%) with a total of 20 alloantibodies, while no autoantibodies were detected. The most frequent alloantibody was anti-E, followed by anti-D, anti-K, anti-C^w, anti-C, anti-c and anti-Le^a. Ethnicity was an important predictor of alloimmunization, while age at start of transfusion (>2 vs. ≤2 years) (p?=?0.005), Rhesus D (RhD) negative status (p?=?0.0017) and history of previous transfusion reactions (p?=?0.007) showed a statistically significant higher rate of alloimmunization. However, patients’ age, gender, number of units transfused, underlying diagnosis and splenectomy were not significantly associated with alloimmunization. Based on our observations, measures to reduce alloimmunization rates may include extended matching for Rhesus and Kell antigens and early initiation of blood transfusions.     

Red Cell Alloantibodies in Patients with Thalassemia

We present the results of tests carried out to detect alloimmunization against red cells in 1,200 patients (607 males and 593 females), transfused and followed up during the period 1981-1987 in our hospital. Of these patients, 1,135 were thalassemic and 65 had sickle cell/beta-thalassemia. In 162 patients who received blood matched for the AB0, rhesus and Kell systems from their first transfusion, the immunization rate was very low (3.7%). In a pilot group consisting of 83 patients with the same clinical characteristics, who received blood matched only for the AB0 and Rh-D antigens, there was a significant difference in the frequency of alloantibodies (15.7%, p less than 0.001). Of 1,038 patients who received blood only matched for AB0 and Rh-D 244 (23.5%) with one or more red cell alloantibodies were identified. Of these 1,038 patients, 973 were exclusively thalassemic. In 220 (22.6%) of them, alloantibodies were found. The sickle cell beta-thalassemia patients presented alloantibodies with a higher frequency (36.9%, 24/65). Only one antibody was found in 114 patients (51.8%) and two or more in 106 patients (48.2%). The alloimmunization significantly concerned the rhesus (34.0%) and Kell (29.8%) systems. Anti-Kell was most often identified (28.5%). Alloimmunization appears considerably lower in patients in whom blood transfusion is started before the age of 3 than in those in whom it is started after that age (20.9 vs. 47.5%, p less than 0.0001).     

Should Chronic Transfusions Be Matched for Antigens Other than ABO and Rho(D)?

It has been recommended that red blood cell transfusions to patients with hemoglobinopathy or aplastic anemia be matched for antigens other than ABO and Rho(D). We studied 1,010 patients with disorders that often lead to repetitive transfusion. The frequency of transfused patients with clinically important antibodies was not significantly different among the disease groups except for those with lymphocytic leukemia. The frequency of multiple red cell antibodies was about 3% overall. Most antibodies (71%) developed early in the transfusion course, before the 15th transfusion. From the standpoints of frequency of alloimmunization, multiplicity of antibodies, and time course of antibody development, patients with hemoglobinopathy and aplastic anemia were not significantly different from other transfused patients. Matching for antigens other than ABO or Rho(D) might increase costs in our hospital by 40,000-370,000 dollars per year for these patients. Because morbidity or mortality due to these antibodies is rare, antigen matching for other than ABO and Rho(D) is not cost-effective.     

Alloimmunization to platelets in heavily transfused patients with sickle cell disease

Bone marrow transplantation (BMT) is now an option for some patients with sickle cell disease (SCD). Many SCD patients are multiply transfused with red blood cells (RBCs), and may be immunized to alloantigens other than erythrocyte antigens. Because platelet refractoriness is a significant complication during BMT, we wished to determine the prevalence of alloimmunization to platelets in transfused SCD patients. Sera collected from 47 transfused and 14 untransfused SCD patients were screened for HLA and platelet-specific antibodies. Transfusion and RBC antibody histories were reviewed. A subset of the patients were rescreened 1 year later. Eighty-five percent of patients with at least 50 RBC transfusions (22 of 26), 48% of patients with less than 50 transfusions (10 of 21), and none of 14 untransfused patients demonstrated platelet alloimmunization (P < .05). Platelet alloimmunization was more prevalent than RBC alloimmunization (20% to 30%). Half of the platelet reactivity was chloroquine-elutable. Eighteen of 22 patients (82%) on chronic RBC transfusion remained platelet-alloimmunized 11 to 22 months after initial testing. In summary, 85% of heavily transfused SCD patients are alloimmunized to HLA and/or platelet-specific antigens. These patients may be refractory to platelet transfusion, a condition that would increase their risk during BMT. Leukodepletion in the transfusion support of SCD patients should be considered to prevent platelet alloimmunization.     

Red cell immunization in multiply transfused Malay thalassemic patients

The development of red blood cell (RBC) isoimmunization with alloantibodies and autoantibodies complicate transfusion therapy in multiply transfused thalassemia patients. Thus, the frequency, causes and prevention of these phenomena were studied among these patients. Clinical and serological data from 58 Malay multiply transfused thalassemic patients who sought treatment at Hospital University Sains Malaysia were collected and analyzed prospectively. Blood samples were subjected to standard blood bank procedures to screen for antibody and subsequent antibodies identification. All patients in our hospital received blood matched for only ABO and Rh (D) antigens. There were 46 (79.3%) patients with Hb E/beta thalassemia, 8 (13.8%) with beta thalassemia major, 3 (5.2%) with Hb H Constant Spring and 1 (1.7%) with Hb H disease. Overall, 8.6% of the patients had alloantibodies and 1.7% had autoantibodies. The alloantibodies identified were anti-E, anti-c, anti-K, anti-Jka, anti-N and anti-S. In conclusion, the transfusion of matched blood is essential for chronically multiply transfused patients in order to avoid alloimmunization. Considering the high frequency of anti E at our hospital, it is advisable to genotype patients and match the red cells for E antigens in multiply transfused thalassemia patients.     

Alloimmunization to red blood cell antigens after universal leucodepletion. A regional multicentre retrospective study

Leucodepletion has been shown to reduce human leucocyte antigen immunization, but studies on the effect of leucodepletion on red cell alloimmunization reported discordant results. We conducted a retrospective multicentre study to determine whether prestorage filter leucodepletion alters the development of clinically significant red blood cell alloimmunization against the Rhesus, Kell, Duffy, Kidd and MSs blood group systems. Two periods were investigated, 2 years before and 2 years after universal leucodepletion. Comparisons were made between the transfused patient cohorts. To control for changes not related to leucoreduction, we compared antibody incidence with antibody prevalence in the two study periods. Newly detected antibodies (n = 4770) were found in 4115 patients from 19 participating hospitals. Of these, 857 antibodies in 659 patients were because of transfusions given in the study periods. The immunization risk was 0.13% for both periods. No differences were found regarding incidence of new antibodies, nor for patients regarding age, sex, previous antibodies, multiple antibodies, additional antibodies, number of transfusions, transfusions episodes and days from transfusion to date of immunization. In conclusion, compared with buffy-coat leucoreduction, universal prestorage filter leucodepletion did not alter the development of clinically significant red blood cell alloimmunization.     

Red blood cell transfusions are associated with HLA class I but not H‐Y alloantibodies in children with sickle cell disease

Blood transfusions can induce alloantibodies to antigens on red blood cells (RBCs), white blood cells and platelets, with these alloantibodies affecting transfusion and transplantation. While transfusion‐related alloimmunization against RBC antigens and human leucocyte antigens (HLA) have been studied, transfusion‐related alloimmunization to minor histocompatibility antigens (mHA), such as H‐Y antigens, has not been clinically characterized. We conducted a cross‐sectional study of 114 children with sickle cell disease (SCD) and tested for antibodies to 5 H‐Y antigens and to HLA class I and class II. Few patients had H‐Y antibodies, with no significant differences in the prevalence of any H‐Y antibody observed among transfused females (7%), transfused males (6%) and never transfused females (4%). In contrast, HLA class I, but not HLA class II, antibodies were more prevalent among transfused than never transfused patients (class I: 33% vs. 13%, P = 0·046; class II: 7% vs. 8%, P = 0·67). Among transfused patients, RBC alloantibody history but not amount of transfusion exposure was associated with a high (>25%) HLA class I panel reactive antibody (Odds ratio 6·8, 95% confidence interval 2·1–22·3). These results are consistent with immunological responder and non‐responder phenotypes, wherein a subset of patients with SCD may be at higher risk for transfusion‐related alloimmunization.     

Red blood cell alloimmunization in sickle cell disease: The influence of racial and antigenic pattern differences between donors and recipients in Brazil

Red blood cell (RBC) transfusions are widely used in the management of patients with sickle cell disease (SCD). However, repeated RBC transfusions are often complicated by RBC alloimmunization. To investigate whether the frequency of RBC alloimmunization could be accounted for by racial and RBC phenotype differences between donors and recipients in Brazil, in this study we compared the RBC phenotype of 100 SCD patients with that observed in 120 randomly selected blood donors. A comparison of the RBC phenotype between the two groups revealed a statistically significant increase in the frequency of the C antigen in the donor population (P < 0.01), but no significant difference was observed for the A, B, D, c, E, e, K, k, Fy^a, M, N, S, s, and Jk^a antigens. Using standard techniques (indirect antiglobulin test, enzyme treatment, and low-ionic-strength solution) we observed an RBC alloimmunization rate of 12.9% (11/85) in the SCD patients. Fifteen alloantibodies were detected in 11 patients, and most (80%) involved antigens in the Rhesus and Kell systems. This observed RBC alloimmunization rate in SCD patients in Brazil is lower than that reported by studies from North America, suggesting that the requirement for extended antigen-matched RBC transfusion for SCD patients in the setting of a RBC phenotype concordant donor-recipient population may not be cost-effective in some countries. © 1996 Wiley-Liss, Inc.     

Alloimmunization and erythrocyte autoimmunization in transfusion-dependent thalassemia patients of predominantly asian descent

The development of hemolytic alloantibodies and erythrocyte autoantibodies complicates transfusion therapy in thalassemia patients. The frequency, causes, and prevention of this phenomena among 64 transfused thalassemia patients (75% Asian) were evaluated. The effect of red blood cell (RBC) phenotypic differences between donors (mostly white) and Asian recipients on the frequency of alloimmunization was determined. Additional transfusion and patient immune factors were examined. 14 (22%) of 64 patients (75% Asian) became alloimmunized. A mismatched RBC phenotype between the white population, comprising the majority of the donor pool, and that of the Asian recipients, was found for K, c, S, and Fyb antigens, which accounts for 38% of the alloantibodies among Asian patients. Patients who had a splenectomy had a higher rate of alloimmunization than patients who did not have a splenectomy (36% vs 12.8%; P =.06). Erythrocyte autoantibodies, as determined by a positive Coombs test, developed in 25% or 16 of the 64 patients, thereby causing severe hemolytic anemia in 3 of 16 patients. Of these 16, 11 antibodies were typed immunoglobulin G [IgG], and 5 were typed IgM. Autoimmunization was associated with alloimmunization and with the absence of spleen (44% and 56%, respectively). Transfused RBCs had abnormal deformability profiles, more prominent in the patients without a spleen, which possibly stimulated antibody production. Transfusion of phenotypically matched blood for the Rh and Kell (leukodepleted in 92%) systems compared to blood phenotypically matched for the standard ABO-D system (leukodepleted in 60%) proved to be effective in preventing alloimmunization (2.8% vs 33%; P =.0005). Alloimmunization and autoimmunization are common, serious complications in Asian thalassemia patients, who are affected by donor-recipient RBC antigen mismatch and immunological factors.     

High risk of transfusion-induced alloimmunization of patients with inflammatory bowel disease

BackgroundAnemia is highly prevalent in inflammatory bowel disease patients, and red blood cell transfusion is often indicated already at reproductive age. Both transfusion and pregnancy may induce red cell alloantibodies, potentially complicating further transfusions and pregnancies. As recent evidence suggests that inflammation may promote red cell antibody induction, the alloimmunization risk of these patients after allogenic erythrocyte exposure was investigated.MethodsRed cell alloantibody status and clinical data were analyzed in 193 inflammatory bowel disease patients with a history of transfusion or pregnancy, and compared with transfused controls with noninflammatory diseases (n = 357).ResultsIn transfused patients with inflammatory bowel disease, a 2.5-fold-increased red cell antibody prevalence was found (10/119, 8.4%), compared with transfused sex-matched controls with noninflammatory diseases (12/357, 3.4%; P = .023). Patients with inflammatory bowel disease had fewer transfusions (mean 3.0 vs 4.2, P = .003) but higher C-reactive protein levels during transfusion than controls (mean 8.4 vs 5.4 mg/dL, P <.001). The red cell antibodies of inflammatory bowel disease patients were clinically significant, directed against different Rh, Kell, Duffy, or Lutheran blood group antigens, and associated with higher number of transfusions (odds ratio 1.57; 95% confidence interval, 1.03-2.39). Conversely, immunomodulatory therapy during transfusion showed negative association (odds ratio 0.12; 95% confidence interval, 0.02-0.61). Only 1.4% of inflammatory bowel disease patients with pregnancy alone had antibodies.ConclusionsPatients with inflammatory bowel disease exhibited a very high risk of transfusion-induced red cell alloimmunization, possibly potentiated by inflammation. Aside from a restrictive transfusion strategy, the implementation of prophylactic blood group phenotype matching of red cell concentrates (not only for ABO and RhD but also RhCcEe, Kell, Kidd, Duffy) could prevent antibody induction and associated complications in these patients.     

Red cell antibodies in patients with homozygous sickle cell disease: a comparison of patients in Jamaica and the United Kingdom

The transfusion history and frequency of red cell antibodies in patients with homozygous sickle cell (SS) disease have been compared in 190 subjects from the Jamaican cohort study and 37 patients attending a sickle cell clinic in Manchester, England. The proportion of patients transfused did not differ between the groups although the number of units transfused and the frequency of red cell antibodies were significantly greater in the Manchester group. Immune antibodies occurred in three Jamaicans (2.6% of those transfused) and 16 UK subjects (76% of those transfused). Multiple antibodies occurred in 10 (63%) UK subjects but in no Jamaicans. Indications for transfusion also differed between the groups, Jamaican patients typically receiving 1-2 units for acute anaemia or acute chest syndrome, whereas UK patients frequently had multiple transfusions in preoperative exchange or prophylaxis programmes. The greater red cell alloimmunization among UK patients probably reflects both the greater use of transfusion and the disparity between donor and recipient populations in the UK.     

Alloimmunization to Red Cell Antigens in Thalassemia: Comparative Study of Usual versus Better-Match Transfusion Programmes

Transfusion records and serological data concerning 120 regularly transfused thalassemic children were followed up, beginning with their first transfusion, for a 5-year period. All patients had been phenotyped for 18 red cell antigens before their first transfusion. The usual-match (UM) group consisted of 64 children who received blood compatible with their ABO and Rho (D) antigens. The better-match (BM) group comprised 56 children who received blood compatible with ABO, CcDEe and K antigens. It was found that a statistically significant difference does not exist in the overall frequency of alloimmunization between the UM (23.43%) and BM group (14.28%) and also between the children that started transfusion therapy before they were 12 months old regarding UM (9%) and BM policies (5.2%). However, a large numerical difference, which might become statistically significant with a larger number of patients was observed in the group of children who were started on transfusions after they were 12 months old, between the UM (38.7%) and BM (18.9%) policy. Finally, a statistically significant difference (less than 0.005) was found only between the children that started transfusions early (7.69%) and those that started them later in life (27.9%), irrespective of the transfusion policy observed. We report, in this study, the mean transfusion numbers of immunized and nonimmunized patients and the frequency, specificity and clinical significance of the identified antibodies are analyzed. Our conclusion is that a BM policy in transfusion programmes, including at least the Rhesus and Kell antigens, is recommended for all thalassemic children that start transfusion therapy after they are 12 months of age; if they start earlier, observation of the BM policy is not necessary.     

Prevalence,Specificity and Titration of Red Cell Alloantibodies in Multiparous Antenatal Females at a Tertiary Care Centre from North India

Screening and detection of clinically significant antibodies among antenatal women plays an important role in transfusion safety and preventing hemolytic disease of fetus and newborn. Routine screening of antenatal women for antibodies is not done in all blood centres of our country and so immunization rates are not known in pregnant women. We studied the prevalence of alloantibodies and titration of Anti D among antenatal multiparous women in Jammu region. In present prospective study, 750 antenatal multiparous women attending antenatal clinics were typed for ABO and D antigens. Alloantibody screening was done, if positive, specificity of alloantibody was ascertained by using commercially available red cell panel by tube method. Rate of alloimmunization was correlated with Rh D status, gravida, previous transfusion history and bad obstetric history. Titration of alloantibody D was done in first and third trimester of pregnancy. In present study most common blood group detected was B positive (38.4 %). Rh D negative cases constituted 7.6 % of total cases. Rate of alloimmunization was 2 %. A significant correlation was seen between Rh D-negative and alloimmunization (21 % in D-negative and 0.45 % in D-positive). There is significant increasing degree of alloimmunization with increase in Gravida. Alloimmunization in females with bad obstetric history was high (4.41 %) as compared to females with no bad obstetric history showing only 1.76 %. Alloantibodies detected were Anti-D, Anti-E, Anti-C and Anti-K. Anti-D constituted 80 % of all alloantibodies detected. Six women in their third trimester had raised titers of anti-D. Most common alloantibody detected was anti-D (80 %). Alloantibodies to other Rh antigens and Kell blood group systems were also identified. To minimize alloimmunization in Rh D negative women, proper Anti D immunoprophylaxis should be implemented.     

Detection and Identification of Red Cell Alloantibodies in Multiply Transfused Thalassemia Major Patients: A Prospective Study

Life long red blood transfusion remains the main treatment for β thalassemia major patients. The development of alloantibodies complicates transfusion therapy in thalassemia patients. Alloimmunization to red cell antigens is one of the most important immunological transfusion reaction and causes delayed type of transfusion reaction. A prospective study was conducted from January 2007 to January 2010. This was a cohorts of 115 patients were selected from regular transfusion group and they were followed for two and half year. They were followed up for the effect of transfusion during study period. There was a decline in patient number from 115 to 96 due to mortality and transfer of patient. A total of 96 multiply transfused thalassemia patients were prospectively included in this study and three consecutive samples collected after every 6 months and investigated for the development of alloantibody to red cell antigens. Tests for antibody screening and identification were performed on preserved sample to investigate prevalence and development of red cell alloimmunization by standardized laboratory techniques by same person at Prathama Blood Centre. A total of 96 patients were included in the study. 63 patients were males and 33 females. A total of five single alloantibodies were formed in five patients out of them four (80 %) belonged to Kell blood group system and one (20 %) from Rh system. It was observed that two (1.92 %) of new thalassemia patients developed red cell alloantibodies during study period. Red cell alloimmunization should be kept in mind in the patients receiving multiple transfusions. In present study, alloimmunization rate was 5.21 %. Mean transfusion duration in these patients was 23.90 days, probably due to presence of alloantibody. RBC alloantibody detection on regular interval and corresponding antigen negative blood transfusion is strongly recommended in transfusion dependent thalassemia patients.     

Post-transfusion alloimmunization in patients with sickle cell disease.

The transfusion histories over a 33-month period of 50 patients with sickle cell disease were reviewed to determine the frequency of alloimmunization to red cell antigens following transfusion in these patients. There were 30 females and 20 males, aged 19--49 years. Eighteen (36%) were immunized of which thirteen were females. Five of the patients have formed only one antibody so far, while the other 13 have formed two or more. Thirty-six antibodies were identified: 16 against various Rh antigens, 12 anti-Lewis, 5 anti-Kell and one each of anti-Jka, -Fya and -M. The immunized patients received, on the average, more transfusions although there was a considerable degree of overlap between the immunized and nonimmunized groups. An approach to the hemotherapy of patients with sickle cell disease (SCD) is discussed.     

Current issues with blood transfusions in sickle cell disease

With increased recognition of the profound morbidity of sickle cell disease and with growing evidence of the efficacy of transfusion therapy in prevention and treatment of sickle cell complications, most patients now receive intermittent transfusion therapy. The purpose of this report is to review blood component therapy and its risks for sickle cell patients. Packed red cells are the preferred blood component. Leukocyte-reduced units should be standard because of their beneficial effects in reducing alloimmunization, transfusion reactions, platelet refractoriness, and infection transmission. The use of washed, frozen, or irradiated units is limited to specific problems. Sickle trait-positive units function normally, but because of difficulties with calculating hemoglobin S percentages and leukocyte filters, they are not routinely used. Transfusion-acquired infections have shown a marked decrease but still present a major risk. Viral hepatitis transmission is currently low, but at least 10% of adult sickle cell patients are hepatitis C positive, and they often have liver damage. Although bacterial infections are rare, they account for 16% of transfusion-related fatalities. Patients who are iron overloaded are particularly vulnerable to Yersina enterocolitica. Red cell alloimmunization is a serious problem that could potentially affect 50% of transfused patients. However, preventive phenotypic matching for common antigens can minimize alloimmunization; limited matching for at least E, C, and K has become the standard of care. Recently, more patients are being identified who have developed red cell autoantibodies, which can mask alloantibodies and occasionally are hemolytic. Careful laboratory evaluation of all cases is essential. Transfusions also may trigger sickle cell events, including pain crises, stroke, and acute pulmonary deterioration. In part, these are induced by blood viscosity and increased blood pressure. Diuretic therapy and close monitoring of transfusion volume and vital signs can minimize these events. In summary, transfusion therapy carries risks, but the routine use of leukocyte-reduced, phenotypically matched units in conjunction with close monitoring of patients can make transfusion therapy safer.     

Red blood cell alloimmunization in sickle cell disease and in thalassaemia: current status,future perspectives and potential role of molecular typing

Red blood cell (RBC) transfusions are a milestone in the treatment for sickle cell anaemia (SSA) and for thalassaemia. RBC alloimmunization remains a major challenge of chronic transfusion therapy, and it can lead to adverse life‐threatening events. The alloimmunization risk could depend on multiple factors such as the number of transfusions and, most of all, the genetic background. Different ethnic groups are predisposed to immunization because of a significant degree of RBC antigenic mismatch between donor and recipient. There is no universal agreement and standards for the most appropriate selection of RBC units in chronically transfused subjects. Current practice only deals with compatibility of ABO, Rh and K antigens. Molecular RBC antigenic matching extended to other blood group systems is an innovative strategy to ensure a better quality and effectiveness of transfusion therapy.