Studies on Rh prophylaxis. II. Rh immune prophylaxis after transfusion with Rh-positive blood

Not as "D"eadly as once thought - the risk of D-alloimmunization and hemolytic disease of the fetus and newborn following RhD-positive transfusion in trauma

The use of blood products to resuscitate injured and massively bleeding patients in the prehospital and early in-hospital phase of the resuscitation is increasing. Using group O red blood cells (RBC) and low titer group O whole blood (LTOWB) avoids an immediate hemolytic reaction from recipient's naturally occurring anti-A and - B, but choosing the RhD type for these products is more nuanced and requires the balancing of product availability and survival benefit against the risk of D-alloimmunization, especially in females of childbearing potential (FCP) due to the possible future occurrence of hemolytic disease of the fetus and newborn (HDFN). Recent models have estimated the risk of fetal/neonatal death from HDFN resulting from D-alloimmunization of an FCP during her trauma resuscitation at between 0-6.5% depending on her age at the time of the transfusion and other societal factors including trauma mortality, her age when she becomes pregnant, frequency of different RHD genotypes in the population, and the probability that the woman will have children with different fathers; this is counterbalanced by an approximately 24% risk of death from hemorrhagic shock. This review will discuss the different models of HDFN outcomes following RhD-positive transfusion as well as the results of recent surveys where the public was asked about their preferences for urgent transfusion in light of the risks of fetal/neonatal adverse events.

Management of Wrong Blood Transfusion to an RhD Negative Woman in Labor

Blood transfusion is life-saving in massive hemorrhage. Before pre-transfusion tests with ABO and RhD typing results are available, O RhD negative packed red blood cell (PRBC) units are used without cross-matching in emergency. RhD negative girls and women of child-bearing age should always receive RhD negative blood transfusions to prevent RhD-alloimmunization because anti-D-related hemolytic disease of fetus and newborn (HDFN) can result in mild to severe anemia, and in a worst-case scenario death of an RhD positive fetus and/or newborn. However, "wrong blood to wrong patient" happens unintentionally. Here we report an emergency blood transfusion with one unit of RhD positive PRBCs to an RhD negative young woman when estimated blood loss was 2500 mL during delivery and surgical removal of retained placenta. Realizing the mistake, management with high dose anti-D immunoglobulin (Ig) was initiated to remove the RhD positive red blood cells (RBCs) from the patient's circulation. Such mitigation is recommended only for girls and women of child-bearing age. Follow-up was performed by flow cytometry until RhD positive RBCs were no longer detected. Ten months after the delivery, antibody screening was negative. However, we still do not know whether we managed to prevent RhD-alloimmunization.

Anti-D Alloimmunization After RhD Positive Red Cell Transfusion to Selected RhD Negative Patients

Transfusion of RhD positive red cells to RhD negative individuals is not routine transfusion practice for the fear of alloimmunization. Aim of this study was to prospectively evaluate rate of alloimmunization after transfusion of RhD positive red cells in RhD negative individuals and to assess delay in transfusion due to decision making. This was a prospective, observational study conducted from 2014 to 2018. All patients were followed up for a period of three months, at 3, 14, 45 and 90 days with antibody screening. In addition, patients who were immunosuppressed and alloimmunized were followed up at 6 months and one year. During the period of the study, there were a total of 57 RhD negative patients (52 males and five females) who received a mean of 4.42 ± 2.85 transfusions. Alloimmunization was detected in 8 (14.03%) patients at a mean interval of 25.63 ± 16.04 days. Anti-D was detected in seven and one patient developed anti-E alloantibody. Mean number of red cell units transfused in alloimmunized was 1.7 ± 0.26 while it was 5.4 ± 1.82 in non-alloimmunized group. There was no delay in providing units to these patients. The TAT was found to be 68 min. Rate of alloimmunization after transfusion of RhD positive red cells to RhD negative individuals was found to be 12.3%. In life saving conditions, RhD negative patients can be transfused RhD positive red cells without delay in decision making.

Incidence of anti-D alloimmunization in D-negative individuals receiving D-positive red blood cell transfusion: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

The transfusion of D-negative red blood cells (RBCs) to D-negative patients has been widely adopted to prevent anti-D alloimmunization, especially in women of childbearing age. Still, transfusion of D-positive RBCs to D-negative recipients is occasionally inevitable in practice, and the resulting incidence of anti-D in different D-negative groups of patients has not been well summarized.

MATERIALS AND METHODS

We searched the relevant literature using PubMed, Cochrane Library, and Embase databases from inception date to 30 September 2021. We looked for studies of anti-D occurring in D-negative recipients who received D-positive RBC transfusions. The anti-D incidence was summarized with 95% confidence intervals (CIs). Data with similar characteristics were combined using a random-effects model.

RESULTS

About 42 studies (2226 cases), which found anti-D, the exact volume of D-positive RBC transfused, and the follow-up time for anti-D detection, met the inclusion criteria. The pooled anti-D incidence was 64% (95% CI, range 55%-74%) in volunteers receiving small volumes of D-positive RBCs, 84% (95% CI, 74%-94%) in those receiving whole units, 26% (95% CI, 19%-32%) in mixed patients, 12% (95% CI, 8%-16%) in oncology patients, 27% (95% CI, 13%-40%) in trauma patients, 4% (95% CI, 0%-8%) in immune-compromised transplant patients, and 6% (95% CI, 1%-39%) in those with AIDS.

CONCLUSION

Compared with the high frequency of anti-D in healthy D-negative volunteers given D-positive RBCs, we found a lower rate of anti-D immunization in various D-negative patients and almost none in transplant and AIDS patients.

Red cell alloimmunization among antenatal women attending tertiary care center in Jamnagar, Gujarat, India

BACKGROUND

The following study was conducted to measure the presence of alloantibodies of Rh and other blood group antigens produced due to fetomaternal hemorrhage in all antenatal women as well as those leading to hemolytic disease of fetus and newborn; presenting to a tertiary care center, G.G. Government Hospital, Jamnagar, Gujarat, India, between April 2014 and March 2016 (2 years).

MATERIALS AND METHODS

All multiparous women irrespective of their period of gestation or obstetrics history were included whereas those having taken anti-D immunoprophylaxis or with a history of blood transfusion were excluded. Antibody screening and identification were done using Bio-Rad ID microtyping system.

RESULTS

Out of total 8920 multigravida females, 8488 were D-antigen positive whereas 432 were D-antigen negative. A total of 126 antibodies among 117 females (1.31%) were found; out of them, 33 were found in D-antigen positive females (0.39%) and 84 in D-antigen negative ones (19.44%) looking at overall frequency of other antibodies such as anti-C: 9, anti-c: 9, anti-E: 13, anti-Cw: 1, anti-M: 5, anti-S: 8, anti-Fya: 3, and anti-D: 78; it was found that anti-D is the most common.

CONCLUSION

The rate of alloimmunization in D-antigen negative women was found to be very high as compared to other studies in western region; hence, strict follow-up of immunoprophylaxis of all Rh D-negative women needs to be taken care of. Apart from this, D-antigen-positive women also show alloimmunization against various antigens giving the prevalence of 0.39%; hence, it should be mandatory that there should be one standard universal protocol for screening of all antenatal women.

Clinical practices and outcomes of RhD immunoglobulin prophylaxis following large-volume fetomaternal haemorrhage in Queensland, Australia

BACKGROUND

Guidelines for laboratory assessment of fetomaternal haemorrhage (FMH) was published by the Australian and New Zealand Society of Blood Transfusion (ANZSBT) in 2002. However, data on adherence by practitioners and clinical outcomes are lacking.

AIMS

The primary objective is to examine the follow-up testing and dosing of additional RhD immunoglobulin in RhD negative women who experienced large-volume FMH for whom additional intravenous RhD immunoglobulin was requested in Queensland, Australia. The secondary objectives are to examine the rate and risk factors of RhD alloimmunisation in these women.

MATERIALS AND METHODS

RhD negative women with FMH >6 mL for whom additional dose(s) of intravenous RhD immunoglobulin was requested through Australian Red Cross Lifeblood from February 2007 to February 2018 were identified. For each patient, the volume of FMH, methods and timing of FMH quantitation, dose of RhD immunoglobulin, maternal and cord blood groups were analysed against the corresponding antibody screen and identification.

RESULTS

Following FMH >6 mL, only 15% and 11.5% of cases adhered to current ANZSBT guideline on follow-up testing and supplemental RhD immunoglobulin dosing respectively. Despite the provision of single supplemental RhD immunoglobulin at a ratio of 100 IU to 1 mL fetal red cells, the rate of RhD alloimmunisation in RhD negative women with RhD positive fetus or fetus of unknown RhD status following FMH >6 mL is at least 4%.

CONCLUSIONS

Poor compliance with guidelines for follow-up and management of large-volume FMH may contribute to increased risk of RhD alloimmunisation. Further analysis of data is warranted.

Red blood cell alloimmunisation after platelet transfusion (excluding ABO blood group system)

Red blood cell alloimmunisation after transfusion of red blood cell concentrates carries a risk for every recipient. This risk is particularly high for patients with conditions such as sickle cell disease. However, red blood cell alloimmunisation can also occur after platelet concentrate transfusion. All blood group systems other than ABO are affected, and there are several mechanisms responsible for this alloimmunisation. The practical implications of this are a need to match red blood cell concentrates in all alloimmunised patients and, in pregnant women, recongnition of the risk of developing haemolytic disease of the foetus and newborn. Several measures can be taken to prevent alloimmunisation: in the case of the D antigen, for example, anti-RhD immunoglobulins can be infused before transfusing platelet concentrates from an RhD-positive donor in a RhD-negative recipient.

How do I manage O- red blood cell inventory

Currently there are no widely accepted guidelines regarding the appropriate use of O- red blood cells (RBCs). Although there has been a decline in overall RBC utilization since 2010, the use of O- RBCs has continued to proportionally increase over this time period resulting in frequent shortages. When faced with these shortages, we implemented some simple strategies that resulted in a significant decrease in annual O- RBC utilization from 10% to 7.5% despite an increase in total RBC utilization. These strategies included collaboration with the clinical staff, improving practices within the blood bank, and having our health system partner with our blood supplier. Herein, we detail our strategies for hospital transfusion services to improve O- RBC utilization. Most of these can be easily implemented and do not require additional resources.

Mitigation strategies for anti-D alloimmunization by platelet transfusion in haematopoietic stem cell transplant patients: a survey of NCCN® centres

BACKGROUND AND OBJECTIVES

D-negative patients are at risk of developing an alloantibody to D (anti-D) if exposed to D during transfusion. The presence of anti-D can lead to haemolytic transfusion reactions and haemolytic disease of the newborn. Anti-D alloimmunization can also complicate allogeneic haematopoietic stem cell transplantation (HSCT) with haemolysis and increased transfusion requirements. The goal of this study was to determine whether cancer centres have transfusion practices intended to prevent anti-D alloimmunization with special attention in patients considered for HSCT.

METHODS AND MATERIALS

To understand transfusion practices regarding D-positive platelets in D-negative patients with large transfusion needs, we surveyed the 28 cancer centres that are members of the National Comprehensive Cancer Network^® (NCCN^® ).

RESULTS

Nineteen centres responded (68%). Most centres (79%) avoid transfusing D-positive platelets to RhD-negative patients when possible. Four centres (21%) avoid D-positive platelets only in D-negative women of childbearing age. If a D-negative patient receives a D-positive platelet transfusion, 53% of centres would consider treating with Rh immune globulin (RhIg) to prevent alloimmunization in women of childbearing age. Only one centre also gives RhIg to all D-negative patients who are HSCT candidates including adult men and women of no childbearing age.

CONCLUSION

There is wide variation in platelet transfusion practices for supporting D-negative patients. The majority of centres do not have D-positive platelet transfusion policies focused on preventing anti-D alloimmunization specifically in patients undergoing HSCT. Multicentre, longitudinal studies are needed to understand the clinical implications of anti-D alloimmunization in HSCT patients.

Strategies to develop a prophylaxis for the prevention of HPA-1a immunization and fetal and neonatal alloimmune thrombocytopenia

Anti-HPA-1a-antibodies are the main cause of fetal and neonatal alloimmune thrombocytopenia (FNAIT) which may result in intracranial hemorrhage (ICH) and death among fetuses and newborns. Advances in understanding the pathogenesis of FNAIT and proof of concept for prophylaxis to prevent immunization suggest that development of hyperimmune anti-HPA-1a IgG aimed at preventing immunization against HPA-1a and FNAIT is feasible. Anti-HPA-1a IgG can be obtained either by isolating immunoglobulin from already-immunized women or by development of monoclonal anti-HPA-1a antibodies. Here we discuss recent advances that may lead to the development of a prenatal and postnatal prophylactic treatment for the prevention of HPA-1a-associated FNAIT and life-threatening FNAIT-induced complications.

IgG-mediated immune suppression in mice is epitope specific except during high epitope density conditions

Specific IgG antibodies, passively administered together with erythrocytes, suppress antibody responses against the erythrocytes. Although used to prevent alloimmunization in Rhesus (Rh)D-negative women carrying RhD-positive fetuses, the mechanism behind is not understood. In mice, IgG suppresses efficiently in the absence of Fcγ-receptors and complement, suggesting an Fc-independent mechanism. In line with this, suppression is frequently restricted to the epitopes to which IgG binds. However, suppression of responses against epitopes not recognized by IgG has also been observed thus arguing against Fc-independence. Here, we explored the possibility that non-epitope specific suppression can be explained by steric hindrance when the suppressive IgG binds to an epitope present at high density. Mice were transfused with IgG anti-4-hydroxy-3-nitrophenylacetyl (NP) together with NP-conjugated sheep red blood cells (SRBC) with high, intermediate, or low NP-density. Antibody titers and the number of single antibody-forming cells were determined. As a rule, IgG suppressed NP- but not SRBC-specific responses (epitope specific suppression). However, there was one exception: suppression of both IgM anti-SRBC and IgM anti-NP responses occurred when high density SRBC-NP was administered (non-epitope specific suppression). These findings answer a longstanding question in antibody feedback regulation and are compatible with the hypothesis that epitope masking explains IgG-mediated immune suppression.

Platelet Transfusion Induces Alloimmunization to D and Non-D Rhesus Antigens

Background

Platelet concentrates (PC) contain residual contaminating red blood cells (RBC), being higher in pooled buffy coat PC (BC-PC) than in apheresis units (AP-PC). Data about PC-induced alloimmunization against non-D Rhesus (Rh) antigens are limited.

Methods

For all newly detected RhD and non-D alloantibodies between August 2015 and September /2017 we prospectively evaluated if they were triggered through PC by analyzing for incompatible RBC and/or PC transfusions.

Results

We found 5,799 positive results in 89,190 antibody screening tests. We identified 13 newly detectable Rh antibodies through incompatible PCs in 11 patients: 6× anti-D, 4× anti-E, 2× anti-c, 1× anti-f. They received a total of 156 PC (83 BC-PC; 73 AP-PC): 5 patients received incompatible BC-PC only, 1 patient received incompatible AP-PC only, 5 patients received incompatible BC-PC and AP-PC. Quality control showed a mean (range) of 0.304 (0.152-1.662) and 0.014 (0.003-0.080) × 10⁹ RBC/l for BC-PC and AP-PC, respectively. Ten of the 11 patients received RBC transfusions, all of them being antigen-negative for the alloantibodies identified.

Conclusions

PC transfusions may not only induce RhD alloimmunization, but also immunization against further Rh antigens such as c, E, and f. The risk seems higher for BC-PC than for AP-PC. The results may have impact on future recommendations of PC transfusion with respect to Rh compatibility and upper limits of RBC contamination.

How do I implement a whole blood program for massively bleeding patients?

Building on the successful military experience, interest has been rekindled in transfusing whole blood (WB) early in the resuscitation of traumatically injured civilians, often before their ABO group is known. WB efficiently provides treatment for shock and coagulopathy, as well as platelet hemostatic function, to patients losing large volumes of blood. Unlike group O uncrossmatched red blood cells (RBCs), group O WB contains a substantial amount of plasma, which is incompatible with the RBCs of all non-group O recipients. Thus, when implementing a WB program, it is important to decide how to mitigate the risk of immune-mediated hemolysis. Other questions that a hospital needs to answer before implementing a WB program include determining which patients will be eligible for this product, how many units eligible patients can receive, for how long it should be stored and under what conditions, and how to monitor for adverse events. The donor center needs to consider if the WB should be leukoreduced, how to comply with the AABB's transfusion-related acute lung injury risk mitigation standard, and into which storage solution it should be collected. This report describes the multidisciplinary approach taken to implementing a civilian WB program at a multihospital health care system in the United States.

Structural and functional impacts of amino acid substitutions that create blood group antigens: implications for immunogenicity

BACKGROUND

The immunogenicities of polypeptide blood group antigens vary widely. One possible determinant of immunogenicity is antigenic foreignness. The goal was to employ alternative ways of assessing foreignness and determine whether foreignness was related to immunogenicity.

STUDY DESIGN AND METHODS

Foreignness was assessed as the extent of protein functional disruption caused by the exofacial amino acid (AA) substitutions that create blood group antigens, using AA substitution prediction algorithms such as Meta-SNP and according to whether those substitutions were radical or conservative.

RESULTS

AA substitutions that create the most immunogenic antigens had the highest Meta-SNP scores, predictive of greater protein structure and function changes. Four of the 11 exofacial AAs that distinguish the most immunogenic antigen, RhD, from RhCE, and substitutions creating four of the five next most immunogenic antigens had the highest Meta-SNP scores (0.293-0.649). Excluding the outlier Jk^a , the mean Meta-SNP score of the four most immunogenic non-RhD antigens (K, Lu^a , E, c) was 3.7-fold higher than the mean of the four least immunogenic (M, Fy^a , C, S), 0.459 versus 0.123 (p = 0.0026). Regression analysis revealed a relationship between immunogenicity and Meta-SNP score (R²  = 0.953). Actual protein functional disruption was predicted for the AA substitution creating the E antigen. An AA cluster at Positions 350, 353, and 354 of RhD was unique, containing radical substitutions according to two classification schemes and relatively high Meta-SNP scores (0.351-0.432).

CONCLUSION

The immunogenicity of blood group antigens was related to the functional disruption caused by the AA substitutions that create the antigens, as measured by Meta-SNP score.

Rare and transient anti-D antibody response in D(-) liver transplant recipients transfused with D(+) red blood cells

A retrospective analysis was conducted on 20 D(-) liver transplant (LT) recipients transfused with D(+) RBCs perioperatively and screened for RBC antibodies between 2 and 6 months later. None developed anti-D detectable by the indirect antiglobulin test. Two patients produced weak anti-D that reacted only with papain-treated RBCs at 10 and 11 days without any sign of immune haemolysis. Antibodies became quickly undetectable. These data suggest an unusual pattern of alloimmunization in LT recipients with rapid, weak and transient antibody response and support the safety of transfusing D(+) RBCs in most of D(-) patients during LT surgery.

Rhesus Negative Woman Transfused With Rhesus Positive Blood: Subsequent Normal Pregnancy Without Anti D production

Clinicians sometimes are confronted with the challenge of transfusing haemorrhaging Rhesus (Rh) D negative patients with Rh D positive blood to save their lives. There are concerns about alloimmunization and future haemolytic disease of the newborn in women of the reproductive age. Another fear is transfusion reaction if they receive another Rh D positive blood in future. We present a 32-year-old Rh D negative woman, who had postpartum haemorrhage in her first pregnancy and was transfused with Rh D positive blood because of unavailability of Rh D negative blood. She did not receive anti D immunoglobin but subsequently had a normal term pregnancy of an Rh positive fetus without any detectable anti D antibodies throughout the pregnancy. In life threatening situations from obstetric haemorrhage, transfusion of Rh D negative women with Rh D positive blood should be considered as the last resort.

Prospective Evaluation of a Transfusion Policy of RhD-Positive Red Blood Cells into DEL Patients in China

BACKGROUND

The D antigen is highly immunogenic, requiring only a small quantity of transfused red blood cells (RBCs) to cause alloimmunization in D- immunocompetent recipients. DEL was reported arousing alloimmunization to true Rh- patients. Molecular studies of the RHD gene have revealed that DEL individuals retain a grossly intact RHD gene or have a portion of RHD in their genomes. Avoiding immunization with clinically important antibodies is a primary objective in transfusion medicine.

METHODS

In order to determine whether pregnant DEL women carrying an RhD+ fetus are at risk of anti-D alloimmunization, 808 Rh- pregnant women with a history of gestations or parturitions who regularly visited hospitals for their prenatal anti-D screening and postpartum care from January 2011 to December 2012 were investigated. Samples were analyzed for DEL by PCR with specific primers, PCR-sequence-specific primers (PCR-SSP), reverse transcription-PCR (RT-PCR), PCRrestriction fragment length polymorphism (PCR-RFLP), and by gene sequencing to characterize different alleles.

RESULTS

Among the 808 Rh- pregnant women of our sample, 178 (22.0%) were typed as DEL; 168 DEL samples were confirmed to have the RHD (1,227 G>A) allele, 8 DEL samples were characterized by one base mutation of the RHD (3G >A) allele, and the remaining two DEL samples were determined to carry RHD-CE(4-9)-D or RHD-CE(2-5)-D. The observation of allo-anti-D in two prominent D epitope loss cases confirmed the partial nature of these DEL phenotypes.

CONCLUSIONS

In conclusion, evidence is provided that different DEL genotypes code either for partial or complete D antigen expression. It is suggested that the use of RhD+ RBCs in complete D antigen DEL patients does not induce adverse reaction.

A case for stocking O D+ red blood cells in emergency room trauma bays

BACKGROUND

AABB Standard 5.27 requires transfusion services to have a process for urgent release of blood before completion of compatibility testing. Our institution endorses a policy for the emergency release of group O, D+ red blood cells (RBC; O+ RBC) to males and females at least 50 years of age. Our emergency department (ED) stocks 4 O- RBC units. To determine if O+ RBCs can replace ED O- RBCs, we performed a retrospective review.

STUDY DESIGN AND METHODS

Patients admitted to the ED between January 2001 and August 2011 and transfused emergency-release O- RBCs were identified. Data were collected on sex, age, length of stay, clinical status, ABO/Rh, RBC transfusions, and RBC antibody screen results.

RESULTS

A total of 498 ED O- RBC units were transfused to 268 patients (168 male, 100 female). A total of 322 units were transfused to males and 114 to females at least 50 years of age. Thirty-nine (14%) were D- with 18 receiving O+ RBCs. A total of 109 had follow-up antibody screens; one D- patient developed alloanti-D.

CONCLUSIONS

The findings support the placement of O+ RBCs in the ED. The majority of ED O- RBCs (88%) went to patients who qualified for O+ RBCs; a minority (1.5%) of patients were D- females less than 50 years of age. The rate of alloimmunization was low.

Responder individuality in red blood cell alloimmunization

Many different factors influence the propensity of transfusion recipients and pregnant women to form red blood cell alloantibodies (RBCA). RBCA may cause hemolytic transfusion reactions, hemolytic disease of the fetus and newborn and may be a complication in transplantation medicine. Antigenic differences between responder and foreign erythrocytes may lead to such an immune answer, in part with suspected specific HLA class II associations. Biochemical and conformational characteristics of red blood cell (RBC) antigens, their dose (number of transfusions and pregnancies, absolute number of antigens per RBC) and the mode of exposure impact on RBCA rates. In addition, individual circumstances determine the risk to form RBCA. Responder individuality in terms of age, sex, severity of underlying disease, disease- or therapy-induced immunosuppression and inflammation are discussed with respect to influencing RBC alloimmunization. For particular high-risk patients, extended phenotype matching of transfusion and recipient efficiently decreases RBCA induction and associated clinical risks.

[Platelet transfusion and immunization anti-Rh1: implication for immunoprophylaxis]

Rhesus (Rh) antigens are not expressed on platelets but residual red cells carry the risk of anti-D iso-immunization in transfusion recipients of platelet concentrates (PC). The main theoretical risk associated with this reaction relates to female subjects due to potential obstetrical situations of maternal-foetal Rh incompatibility. Isogroup PC transfusion in this system is therefore advised. However, logistical constraints impose frequent Rh-incompatible transfusions that require the recommendation of anti-Rh immunoglobulin in a girl of childbearing age in this situation. This recommendation, already restricted to a group of patients deserves to be questioned over a decade after being issued. Data from published reports are difficult to interpret because of the heterogeneity of the few series (CP type, immune status, timing of biological tests) but the current techniques for preparing products and most common use of CP apheresis limited the risk of immunization. Moreover, platelet transfusions are particularly relevant to immunocompromised populations which, to what extent (heavy chemotherapy and/or hematopoietic stem cells recipients) seems to be protected from this risk. It is noteworthy that the clinical consequences that may be expected from such immunization are not reported. Although some authors emphasize significant isoimmunization rates (maximum 19%), the heterogeneous conditions and the lack of evidence of clinical consequence suggest evaluating the recommendations or revising them towards more targeted indications of seroprophylaxis.

Does Rh immune globulin suppress HLA sensitization in pregnancy?

BACKGROUND

How Rh immune globulin (RhIG) prevents sensitization to D antigen is unclear. If RhIG Fc delivers a nonspecific immunosuppressive signal, then RhIG may inhibit sensitization to antigens other than D. HLA antibody prevalence was compared in previously pregnant D- versus D+ women to investigate whether RhIG suppresses HLA sensitization.

STUDY DESIGN AND METHODS

In the Leukocyte Antibody Prevalence Study (LAPS), 7920 volunteer blood donors were screened for anti-HLA and surveyed about prior pregnancies and transfusions. A secondary analysis of the LAPS database was performed.

RESULTS

D- women not more than 40 years old (presumed to have received antenatal with or without postpartum RhIG in all pregnancies) had a significantly lower HLA sensitization rate than D+ women (relative risk, 0.58; 95% confidence interval [CI], 0.40-0.83). When stratified by deliveries (one, two, three, or four or more), D- women not older than 40 were HLA sensitized less often than D+ women in every case. In contrast, a clear relationship between D type and HLA sensitization was not seen in older previously pregnant women whose childbearing years are presumed to have preceded the use of routine RhIG prophylaxis. In a multivariable logistic regression model, D- women not more than 40 years old remained significantly less likely to be HLA sensitized compared with D+ women after adjusting for parity, time from last pregnancy, lost pregnancies, and transfusions (odds ratio [OR], 0.55; 95% CI, 0.34-0.88).

CONCLUSION

Consistent with a nonspecific immunosuppressive effect of RhIG, younger previously pregnant D- women were less likely than previously pregnant D+ women to be HLA sensitized.

Intensive red blood cell transfusions and risk of alloimmunization

BACKGROUND

Exposure to allogenic red blood cells (RBCs) may lead to formation of antibodies against nonself-antigens in transfused patients. While alloimmunization rates are known to increase with the number of transfusions, the transfusion course in patients can vary from receiving multiple units during a single transfusion event or getting them dispersed over a long(er) period. In this study we compared the immunization risk between different transfusion intensities.

STUDY DESIGN AND METHODS

An incident new-user cohort study was conducted among consecutive transfused patients at two university medical centers. All patients who received their first RBC transfusion within the study period from January 2005 to December 2011 were eligible. Intensive transfusions were defined as at least 5, at least 10, and at least 20 RBC units within 48 hours. Alloimmunization hazard ratios (HRs), comparing patients receiving intensive transfusions to patients never receiving intensive transfusions, were estimated.

RESULTS

The study cohort was composed of 5812 patients who had received a median of 7 (interquartile range, 4-12) units. RBC alloantibodies were formed by 156 patients. The adjusted Cox regression HRs for alloimmunization, with number of units as the time covariate and adjusted for patient age, sex, and follow-up time after first transfusion, ranged from 0.8 to 1.2 (95% confidence interval, 0.4-2.6).

CONCLUSION

The occurrence of RBC alloimmunization in patients receiving intensive transfusions did not differ significantly from patients receiving nonintensive transfusions.

Platelet transfusion - the art and science of compromise

SUMMARY

Many modern therapies depend on platelet (PLT) transfusion support. PLTs have a 4- to 7-day shelf life and are frequently in short supply. In order to optimize the inventory PLTs are often transfused to adults without regard for ABO compatibility. Hemolytic reactions are infrequent despite the presence of 'high titer' anti-A and anti-B antibodies in some of the units. Despite the low risk for hemolysis, some centers provide only ABO identical PLTs to their recipients; this practice might have other beneficial outcomes that remain to be proven. Strategies to mitigate the risk of hemolysis and the clinical and laboratory outcomes following ABO-matched and mismatched transfusions will be discussed. Although the PLTs themselves do not carry the D antigen, a small number of RBCs are also transfused with every PLT dose. The quantity of RBCs varies by the type of PLT preparation, and even a small quantity of D+ RBCs can alloimmunize a susceptible D- host. Thus PLT units are labeled as D+/-, and most transfusion services try to prevent the transfusion of D+ PLTs to D- females of childbearing age. A similar policy for patients with hematological diseases is controversial, and the elements and mechanisms of anti-D alloimmunization will be discussed.

Emergency uncrossmatched transfusion effect on blood type alloantibodies

BACKGROUND

Trauma patients receive emergency transfusions of unmatched Type O Rh-negative (Rh-) blood until matched blood is available. We hypothesized that patients given uncrossmatched blood may develop alloantibodies, placing them at risk for hemolytic transfusion reactions (HTRs).

METHODS

Data regarding alloantibody profiles and HTR occurrence were collected from the records of trauma patients at our university-based trauma center who received emergency uncrossmatched blood from July 2008 to August 2010.

RESULTS

A total of 132 patients received 1,570 units of packed red blood cells. Mean injury severity score was 28 ± 1.3. Forty-five (34%) patients died: 27 on hospital day 1; the remaining 18 had no evidence of HTR before death. Four Rh- female patients received Rh+ fresh frozen plasma, but none received Rh+ packed red blood cells. Three Rh- male patients received both Rh+ packed red blood cells and fresh frozen plasma, and one received Rh+ fresh frozen plasma. One patient developed anti-Rh D antibodies. None experienced HTR. One female patient had HTR from reactivation of anamnestic JK antibodies. Thirteen (33%) of 39 patients met criteria for HTR based on urinalysis and 29 (40%) of 72 patients tested met criteria for HTR based on hemoglobin and bilirubin values. Only one patient had confirmed HTR.

CONCLUSION

High rates of injury recidivism in trauma patients increase the likelihood of multiple blood transfusions during their lifetime. Rh- patients who receive Rh+ blood are at risk of developing anti-Rh antibodies, putting them at risk for HTR. The conservation of Rh- blood for use in female patients may be detrimental to Rh- male patients. Laboratory diagnostic criteria for HTR are nonspecific in the trauma population and should be used with caution.

Immunogenicity of blood group antigens: a mathematical model corrected for antibody evanescence with exclusion of naturally occurring and pregnancy-related antibodies

Blood group antigen immunogenicity is a crucial factor in red blood cell alloimmunization. Previous calculated estimates of immunogenicity suffered from several key shortcomings. To address these issues we have (1) introduced a correction factor for antibody persistence rates into traditional immunogenicity calculations, (2) calculated immunogenicities only in men to eliminate pregnancy-related antibodies, and (3) excluded antibodies reactive only at room temperature to minimize the contribution of naturally occurring antibodies. With these corrections, we have calculated the immunogenicities of common blood group antigens using data collected on clinically significant alloantibodies (n = 452) in a male patient population. We observed a 3- to 5-fold increase in immunogenicity for some antigens (ie, Jka, Cw, Lua) and smaller changes in others compared with traditionally calculated estimates. In addition, we have calculated the transfusion-related immunogenicities of antigens traditionally associated with naturally occurring antibodies (eg, anti-Lea, -Leb, -M, and -P1).

Prospective evaluation of a transfusion policy of D+ red blood cells into D- patients

BACKGROUND

Although D- patients should receive red blood cells (RBCs) from D- donors, the scarcity of D- blood components in certain situations makes the transfusion of D+ RBCs unavoidable. Therefore it is recommended that guidelines be developed in order to standardize transfusion policy in these scenarios.

STUDY DESIGN AND METHODS

We have prospectively evaluated a policy for the use of D+ RBCs in 905 D- patients. The amount of D- RBCs saved as well as the incidence of hemolytic reactions and anti-D alloimmunization were assessed.

RESULTS

554 patients received D- RBCs while 351 received a total of 1032 D+ RBCs, all of them within our criteria for the acceptable use of D+ RBCs. This strategy allowed us to save 25.6 percent of D- RBCs (1032 out of 4024 RBCs requested). No hemolytic reactions were reported. The incidence of alloimmunization was 21.4 percent. Most patients who developed anti-D did so within the first 2 or 4 RBCs transfused (64% after the first 2 RBCs transfused and 88% after the first 4). In multivariate analysis the age of less than 77 years was the only predictor for alloimmuization (HR = 2.48 [95% CI = 1.21-3.81]; p = 0.014).

CONCLUSION

The use of D+ RBCs in selected D- patients does not induce adverse reactions and allows the saving of a significant number of D- RBCs.

Efficacy of RhD monoclonal antibodies in clinical trials as replacement therapy for prophylactic anti-D immunoglobulin: more questions than answers

Prophylactic anti-D is a very safe and effective therapy for the suppression of D-immunization and prevention of haemolytic disease of the foetus and newborn. The primary mode of action of anti-D is rapid clearance of fetal D-positive red cells from the maternal circulation, mediated by interactions with immunoglobulin G Fc receptors on macrophages in the spleen. Many anti-D monoclonal antibodies (mAb) have been produced by a variety of methods. Twelve anti-D mAbs were tested in eight studies for their ability to mediate clearance of autologous red cells, and 13 antibodies studied in seven trials of the clearance of D-positive red cells injected into D-negative subjects. Antibodies produced by human B-cell lines, mouse-human heterohybridomas and Chinese hamster ovary cells varied in their activity with none being quite as effective as polyclonal anti-D. However, clearance mediated by recombinant anti-D produced by rat YB2/0 cells was extremely rapid, faster than polyclonal anti-D, but with haemolysis and some hepatic accumulation of red cells observed in one study. Two human anti-D mAbs prevented D-immunization. In contrast, anti-D mAbs from heterohybridomas increased the incidence and rapidity of anti-D responses. It is hypothesised that unnatural glycosylation of monoclonal anti-D produced by some cell lines may have caused these unexpected results. In some antibodies, unusual oligosaccharides on anti-D may have affected binding to Fc receptors resulting in reduced red cell clearance. For others, non-human glycoforms of anti-D might have bound to innate immune recognition molecules promoting pro-inflammatory reactions. These extensive data on the clinical activity of monoclonal anti-D produced by cell lines derived from four species will inform the future development of monoclonal anti-D for RhD prophylaxis.

Detection of anti-D in D- recipients transfused with D+ red blood cells

BACKGROUND

The D antigen is highly immunogenic, requiring only a small quantity of transfused red blood cells (RBCs) to cause alloimmunization in D- immunocompetent recipients. The relatively low sensitization rate in oncology patients transfused with D+ platelets is well documented. A study of the alloimmunization rate of primarily nononcology D- recipients transfused with D+ RBCs was undertaken.

STUDY DESIGN AND METHODS

Transfusion service records were examined to identify D- recipients who were not alloimmunized to the D antigen and who had a follow-up antibody screen performed at least 10 days after the initial D+ RBC transfusion(s). The age and sex of the recipients, date and number of D+ RBC transfusion(s) and their leukoreduction status, all subsequent serologic investigations, and the hospital ward where the units were issued were recorded.

RESULTS

There were 98 study-eligible recipients identified who received a total of 445 D+ RBC units. The mean follow-up length was 182 days. Most recipients (87%) had antibody screens performed more than 21 days after the initial D+ RBC transfusion. In total, 24 recipients made 44 new alloantibodies: 22 anti-D (22%), 11 anti-E, 5 anti-C, 2 anti-K, and 1 each of anti-Kp(a), anti-Jk(a), anti-Bg, and anti-Fy(b). The rate of anti-D alloimmunization among recipients of entirely leukoreduced D+ units was 13 percent (1/8). Reexposure to D+ RBCs after the initial bleeding episode did not increase the rate of alloimmunization.

CONCLUSIONS

The 22 percent rate of anti-D alloimmunization in patients requiring urgent RBC transfusion was intermediate between the rates previously reported for D- oncology patients transfused with D+ RBCs and that in immunocompetent volunteer recipients.

Rhesus immune globulin fails to prevent immunization after rhesus incompatible blood transfusion

The transfusion of rhesus positive (D+) red blood cells to a rhesus negative (D-) person usually induces the development of an irregular anti-D antibody in the recipient. This can lead to a hemolytic reaction in subsequent transfusions, and, in women of childbearing age, can lead to fetal erythroblastosis in any future pregnancy. The recommended interventions to avoid the immunization of the recipient include the administration of intravenous rhesus immune globulin within 72 h after the transfusion. We report the case of a D- woman who received one unit of D+ red blood cells and a total of 40 units of D- red blood cells after severe trauma. In spite of treatment with rhesus immune globulin, the patient developed anti-D antibodies.

Prevention of Rh alloimmunization

OBJECTIVE

To provide guidelines on use of anti-D prophylaxis to optimize prevention of rhesus (Rh) alloimmunization in Canadian women.

OUTCOMES

Decreased incidence of Rh alloimmunization and minimized practice variation with regards to immunoprophylaxis strategies.

EVIDENCE

The Cochrane Library and MEDLINE were searched for English-language articles from 1968 to 2001, relating to the prevention of Rh alloimmunization. Search terms included: Rho(D) immune globulin, Rh iso- or allo-immunization, anti-D, anti-Rh, WinRho, Rhogam, and pregnancy. Additional publications were identified from the bibliographies of these articles. All study types were reviewed. Randomized controlled trials were considered evidence of highest quality, followed by cohort studies. Key individual studies on which the principal recommendations are based are referenced. Supporting data for each recommendation is briefly summarized with evaluative comments and referenced.

VALUES

The evidence collected was reviewed by the Maternal-Fetal Medicine and Genetics Committees of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and quantified using the Evaluation of Evidence guidelines developed by the Canadian Task Force on the Periodic Health Exam.

RECOMMENDATIONS

1. Anti-D Ig 300 microg IM or IV should be given within 72 hours of delivery to a postpartum nonsensitized Rh-negative woman delivering an Rh-positive infant. Additional anti-D Ig may be required for fetomaternal hemorrhage (FMH) greater than 15 mL of fetal red blood cells (about 30 mL of fetal blood). Alternatively, anti-D Ig 120 microg IM or IV may be given within 72 hours of delivery, with testing and additional anti-D Ig given for FMH over 6 mL of fetal red blood cells (12 mL fetal blood). (I-A) 2. If anti-D is not given within 72 hours of delivery or other potentially sensitizing event, anti-D should be given as soon as the need is recognized, for up to 28 days after delivery or other potentially sensitizing event. (III-B) 3. There is poor evidence regarding inclusion or exclusion of routine testing for postpartum FMH, as the cost-benefit of such testing in Rh mothers at risk has not been determined. (III-C) 4. Anti-D Ig 300 microg should be given routinely to all Rh-negative nonsensitized women at 28 weeks' gestation when fetal blood type is unknown or known to be Rh-positive. Alternatively, 2 doses of 100-120 microg may be given (120 microg being the lowest currently available dose in Canada): one at 28 weeks and one at 34 weeks. (I-A) 5. All pregnant women (D-negative or D-positive) should be typed and screened for alloantibodies with an indirect antiglobulin test at the first prenatal visit and again at 28 weeks. (III-C) 6. When paternity is certain, Rh testing of the baby's father may be offered to all Rh-negative pregnant women to eliminate unnecessary blood product administration. (III-C) 7. A woman with "weak D" (also known as Du-positive) should not receive anti-D. (III-D) 8. A repeat antepartum dose of Rh immune globulin is generally not required at 40 weeks, provided that the antepartum injection was given no earlier than 28 weeks' gestation. (III-C) 9. After miscarriage or threatened abortion or induced abortion during the first 12 weeks of gestation, nonsensitized D-negative women should be given a minimum anti-D of 120 microg. After 12 weeks' gestation, they should be given 300 microg. (II-3B) 10. At abortion, blood type and antibody screen should be done unless results of blood type and antibody screen during the pregnancy are available, in which case antibody screening need not be repeated. (III-B) 11. Anti-D should be given to nonsensitized D-negative women following ectopic pregnancy. A minimum of 120 microg should be given before 12 weeks' gestation and 300 microg after 12 weeks' gestation. (III-B) 12. Anti-D should be given to nonsensitized D-negative women following molar pregnancy because of the possibility of partial mole. Anti-D may be withheld if the diagnosis of complete mole is certain. (III-B) 13. At amniocentesis, anti-D 300 microg should be given to nonsensitized D-negativeesis, anti-D 300 microg should be given to nonsensitized D-negative women. (II-3B) 14. Anti-D should be given to nonsensitized D-negative women following chorionic villous sampling, at a minimum dose of 120 microg during the first 12 weeks' gestation, and at a dose of 300 microg after 12 weeks' gestation. (II-B) 15. Following cordocentesis, anti-D Ig 300 microg should be given to nonsensitized D-negative women. (II-3B) 16. Quantitative testing for FMH may be considered following events potentially associated with placental trauma and disruption of the fetomaternal interface (e.g., placental abruption, blunt trauma to the abdomen, cordocentesis, placenta previa with bleeding). There is a substantial risk of FMH over 30 mL with such events, especially with blunt trauma to the abdomen. (III-B) 17. Anti-D 120 microg or 300 microg is recommended in association with testing to quantitate FMH following conditions potentially associated with placental trauma and disruption of the fetomaternal interface (e.g., placental abruption, external cephalic version, blunt trauma to the abdomen, placenta previa with bleeding). If FMH is in excess of the amount covered by the dose given (6 mL or 15 mL fetal RBC), 10 microg additional anti-D should be given for every additional 0.5 mL fetal red blood cells. There is a risk of excess FMH, especially when there has been blunt trauma to the abdomen. (III-B) 18. Verbal or written informed consent must be obtained prior to administration of the blood product Rh immune globulin. (III-C) VALIDATION: These guidelines have been reviewed by the Maternal-Fetal Medicine Committee and the Genetics Committee, with input from the Rh Program of Nova Scotia. Final approval has been given by the Executive and Council of the Society of Obstetricians and Gynaecologists of Canada.

Absence of D- alloimmunization in AIDS patients receiving D-mismatched RBCs

BACKGROUND

More than 80 percent of D- patients who receive D+ blood become alloimmunized to the D antigen. Anemia occurs in most AIDS patients at some point in the disease. D- patients with AIDS may require blood transfusion and, during times of blood shortage, may receive D+ RBCs. They would be expected to become alloimmunized to the d antigen.

STUDY DESIGN AND METHODS

The records of the transfusion service between January 1996 and July 2000 were reviewed for D- patients who received D+ blood. IATs were performed before the initial transfusion and subsequently when the patient required further RBC transfusion.

RESULTS

Eight D- AIDS patients who received multiple transfusions (three women and five men; age range, 31-44 years; mean, 44 years) who received between 2 and 11 units (mean, 6.25) of D+ RBCs were identified. Antibody screens were performed at 8 to 65 weeks after transfusion. It was found that none of the eight D- AIDS patients developed anti-D. ABO antibodies were found as expected. During the same period, it was found that six D- patients admitted with other diagnoses who received 1 to 9 units of D+ RBCs, all developed anti-D within 7 to 19 weeks of transfusion.

CONCLUSION

Patients with AIDS may not form alloantibodies to the D antigen. This may be attributable to their immunodepressed state, particularly to the decrease in CD4+ T lymphocytes. Therefore, during blood shortages, transfusion of D+ blood to D- AIDS patients may be without any subsequent consequence.

Absence of D alloimmunization in D- pediatric oncology patients receiving D-incompatible single-donor platelets

BACKGROUND

Guidelines are lacking for prophylaxis against D alloimmunization after D-incompatible platelet transfusion. A rational basis for the application of prophylaxis would be beneficial for institutions in which inventory constraints demand the administration of large numbers of D-incompatible platelets.

STUDY DESIGN AND METHODS

A retrospective analysis was performed of all D-incompatible platelet transfusions administered at a pediatric research hospital over a 1.5-year period. Patients exclusively received single-donor WBC-reduced platelets and did not receive RhIg immunoprophylaxis. Numbers, source, ABO type, duration of serologic follow-up, and level of RBC contamination of D-incompatible transfusions were analyzed. All positive D serologies in the institution over a 3.5-year period were examined to determine cause and potential association with platelet transfusion.

RESULTS

Thirty-five patients not receiving bone marrow transplant and seven bone marrow transplant patients received 490 and 255 D-incompatible transfusions, respectively, over 1.5 years. Patients had various diagnoses, predominantly malignancies. Seventy-nine percent of D-incompatible transfusions were ABO compatible. An estimated 2300 incompatible transfusions were performed over 3.5 years. No case of D alloimmunization was detected.

CONCLUSIONS

D immunoprophylaxis is generally unnecessary in pediatric oncology patients receiving D-incompatible, WBC-reduced, single-donor platelets not visibly contaminated by RBCs. Further studies to validate these observations in the pediatric population and to extend them to other population groups are warranted.