Low-frequency Antigen Research Articles

Identification of Antibody to Low-Frequency Antigen in Thalassemia: Non-specific Allo Adsorption Method

Identification of Antibody to Low-Frequency Antigen in Thalassemia: Non-specific Allo Adsorption Method

Ethnic diversity in Chilean blood groups: A comprehensive analysis of genotypes, phenotypes, alleles and the immunogenic potential of antigens in northern, southern and central regions.

The available information on blood groups in the Chilean population is derived from studies on aboriginal cohorts and routine serological test results. The purpose of this study is to conduct a comprehensive analysis of genotypes, phenotypes and blood group alleles in donors from northern, central and southern Chile using molecular methods. Overall, 850 samples from donors in northern, central and southern Chile were genotyped. Allelic, genotypic and antigenic frequencies were calculated and compared among regions. Of these, 602 samples were analysed by haemagglutination, and discrepancies found between phenotypes and genotypes were investigated. The immunogenic potential of antigens was calculated by the Giblett equation, using the antigenic frequencies of donors from Santiago and the alloantibody frequencies of patients from the same region. Alleles of low prevalence, variant alleles and those responsible for the absence of high-prevalence antigens were found. Significant differences were observed between the antigenic frequencies of the three regions. Discrepancies between serologic and molecular results were mostly attributed to the molecular background affecting antigen expression. In the calculation of the immunogenic potential of antigens, the highest value was attributed to the Dia antigen. These findings represent the first molecular characterization of blood group antigens in Chileans. Our results highlight the necessity of using molecular tools to explore the genotypes underlying variant phenotypes, low-frequency antigens and antigens lacking specific antisera that cannot be detected by haemagglutination. Additionally, they emphasize the importance of understanding the distribution of blood groups among different populations.

Reporting a rare, clinically significant, naturally occurring anti-Cw alloantibody in a whole blood donor: A kingpin in vein-to-vein transfusion chain

Abstract Anti-Cw (C Willis) is a low-frequency immunoglobulin against red cell antigen Cw in the Rhesus (Rh) blood group system. Anti-Cw can either be naturally occurring or develop as a result of red blood cell sensitization through transfusion or during pregnancy, and is rarely associated with clinically significant hemolytic disease of the fetus and newborn. However, anti-Cw, being a low-frequency antigen, is not always included in the commercial antibody screening panels and also not phenotyped for in-house pooled red cells used for single-cell indirect antiglobulin testing for blood donors in various blood centers. Here, we report a case of a whole blood donor who was identified with an anti-Cw antibody.

Hybrids and microconversions in RH genes: investigation and implication in transfusion therapy

: The discovery and characterization of the RH genes, i.e., RHD and RHCE, in the early 90s have been milestones in the field of blood group genetics. In addition to the single nucleotide variants (SNVs), which are commonly considered as the predominant molecular actors resulting in the variability of antigen expression, genetic exchange between both RH genes has been shown to be a frequent mutational mechanism. Indeed, dozens of hybrid alleles and microconversions associated with variant RH phenotype have been reported so far. Interestingly, these alleles display population-specific patterns of distribution. Also, they are directly involved in the qualitative and quantitative alteration of RH antigen expression, which has immediate consequences for diagnostics and transfusion management. Overall, hybrid alleles and microconversions contribute largely to the complexity of the RH blood group system. In the current state of knowledge, this narrative review: (I) defines and introduces the molecular determinants of the genetic exchange in the RH genes; (II) describes how these variant alleles may alter the expression of polymorphic and high-frequency antigens (HFAs) and/or result in the expression of low-frequency antigens (LFAs); (III) reports on their distribution at a low-resolution population scale; and (IV) discusses their relevance and identification in routine clinical practice for transfusion management at the laboratory level.

Severe hemolytic disease of a newborn due to anti-E combined with anti-Mia, anti-Mur and anti-Hil

Background: Common alloantibodies leading to severe hemolytic disease of the fetus and newborn (HDFN) could vary among different ethnic groups. The MNS blood group hybrid glycophorin GP.Mur distributes with a high frequency in the regions of Southeast Asia. Alloantibodies against GP.Mur (anti-‘Mia’) often present as mixture of antibodies against several low frequency antigens. In this study, we first described a case of severe HDFN in Guangzhou, China, which was caused by alloantibodies of anti-E in combination with specificities to the GP.Mur including Mia, Mur and Hil.

Rare Blood Groups in ABO, Rh, Kell Systems - Biological and Clinical Significance.

Background: The frequency of ABO, Rh and Kell blood group antigens differs among populations of different ethnic ancestry. There are low-frequency antigens (<1%) and high-frequency antigens (>90%). A rare blood group is defined as the absence of a high-frequency antigen in the general population, as well as absence of multiple frequent antigens within a single or multiple blood group systems. Aim: To perform red blood cell typing and to calculate the antigen and phenotype frequencies, in order to identify rare blood group donors within the clinically most important АВО, Rh and Kell systems. Material and Methods: АВО, Rh (D, C, E, c, e) and Kell (K) antigen typing was performed using specific monoclonal sera and microplate technique, while Cellano (k) typing was performed with a monoclonal anti-k, antihuman globulin and column agglutination technique. Weak ABO subgroups were determined using the absorption elution method or molecular genotyping (PCR-SSP). Results: ABO antigen frequency is: A (40.89%), O (34.22%), B (16.97%), AB (7.92%) and weak ABO subgroups (0, 009 %). The established genotypes were AxO1 (0, 0026%) and AxB (0, 001%). Rh antigen frequency is: D (85.79%), C (71.7%), c (76.0%), E (26.0%) and е (97.95%). The most common Rh pheno-type is the DCcee (32.7%) while the rarest phenotype is the DCCEE phenotype (0. 003%). The prevalence of K and k antigen is 7.5% and 99.94%, respectively. The frequency of the rare phenotype K+k- is 0.06%. Conclusion: Large scale phenotyping of blood group antigens enables the identification of blood donors with rare blood groups for patients with rare phenotypes or with antibodies to high-frequency antigens and to frequent antigens within one or more blood group systems.

Rare Anti-Cw Antibody

Introduction: Anti-Cw is a low-frequency antibody against Cw (Rh8) antigen, a low incidence antigen of the Rh system. Anti-Cw antibody may cause mild to moderate hemolytic disease of the fetus and newborn (HDFN) and mild to severe immediate or delayed hemolytic transfusion reactions (HTR). The antigenic frequency of Cw in the Indian population is 1.25%. Two cases of Anti-Cw antibody are being reported which were detected during routine antibody screening, one an oncology patient and the other a healthy blood donor. Case 1: A 30-year-old male, known case of acute myeloid leukemia, with previous history of induction chemotherapy and blood transfusion was admitted for further management and chemotherapy. When three cell antibody screening was performed using an automated platform, the screen was positive with +2 reactions. Antibody identification using 14 cells suggested the presence of an Anti-Cw antibody. On further testing, the patient red blood cell (RBCs) were negative for Cw antigen. Case 2: A 20-year-old male, first-time, voluntary blood donor, with no history of blood transfusion donated whole blood. On performing three cell antibody screening using automated platform, screen was found to be positive with +3 reactions. Antibody identification performed using 14 cell panel suggested the presence of Anti-Cw antibody. On further testing, the donor RBCs were negative for Cw antigen. Conclusion: Antibody screening and identification is recommended in pretransfusion testing, especially in multi-transfused patients and patients belonging to the reproductive age group, so that antibody to low-frequency antigen can be detected and its potential to cause HTR and HDFN can be assessed.

Alloimmunization and Autoimmunization in Adult Transfusion Dependent Beta Thalassemia Major Patients: Report from a Comprehensive Center in Israel

BACKROUND: Survival of patients with transfusion dependent (TD) beta thalassemia major (TM) has improved significantly over the past few decades as better treatment became available. However, due to ineffective erythropoiesis, reduced red blood cell (RBC) survival, and subsequent continuous hemolytic anemia, these patients are regularly and heavily transfused since early childhood. Exposure to multi transfusions is associated with significant risks including development of antibodies against RBC antigens, both alloantibodies and autoantibodies, which in turn complicate RBC cross matching, shorten in vivo survival of transfused RBC, and may accelerate tissue iron loading. Anti-K, anti-E and other Rh blood group system alloantibodies are the most frequently detected.AIMS: Assessment of RBC alloimmunization and autoimmunization rate in adult patients with TD TM followed and treated in our center.PATIENTS and METHODS: The study included a total of 40 patients with TD TM, >18 years of age. Clinical and transfusion records, including age, gender, ethnicity, history of pregnancies, blood group, history of splenectomy, age at first transfusion and lifelong cumulative number of blood units transfused, were retrieved from patients' files and from the blood bank database.RESULTS: Twenty one (52.5%) patients were males, 19 (47.5%) were females, the mean ±SD (range) age was 31.8 ± 6.9 (20-47) years, 29 patients (72.5%) were of Muslim Arab origin, 11 (27.5%) were Jewish. Thirty (75.0%) of the patients were splenectomized (SPX). The median (mean) ±SD (range) age at first transfusion was 0.71 (1.07) ± 0.93 (0.25-4.0) years, and the mean ±SD (range) of lifelong cumulative number of blood units transfused was 828.5 ± 239.3 (439-1363).Alloimmunization was demonstrated in 17 (42.5%) patients; 10 of 21 (47.6%) males and 7 of 19 (36.8%) females; 11 of 29 (37.9%) of Muslim Arab origin, 6 of 11 (54.5%) of Jewish origin; 11 (64.7%) had >1 alloantibody. Among female patients, alloimmunization was demonstrated in 4 (31.0%) of 13 with no history of pregnancy and in 3 (50.0%) of 6 with history of pregnancy. Twelve (40.0%) of 30 SPX patients had alloantibodies, compared to 5 (50.0%) of 10 patients with intact spleen.Anti-Rh antibodies were the most prevalent, detected in 10/17 (58.8%) patients having 12 alloantibodies (8 anti-E, 2 anti-D, 1 anti-C and 1 anti-Cw), followed by Anti-Kell antibodies detected in 7/17 (41.2%) patients having 8 alloantibodies (6 anti-K, 2 anti-Kpa). One patient had anti-Jkb, and 3 patients had alloantibodies against low frequency antigens. Autoimmunization was demonstrated in 2 (5.0%) patients (Figure 1).Significant inverse correlation was found between age at first transfusion and rate of alloimmunization. Thirty (75.0%) patients started blood transfusions before 1 year; 9 (30.0%) of them had alloantibodies. Ten (25.0%) patients started blood transfusions after the first year; 8 (80.0%) of them had alloantibodies (p=0.009).There was no significant association between alloimmunization and patients' age, gender, ethnicity, history of pregnancies, blood group, splenectomy status, and lifelong cumulative number of blood units transfused (p >0.05).CONCLUSIONS: We have found a high rate (42.5%) of alloimmunization in adult TD TM patients, which might be attributed to multi transfusions over many years without RBC antigen matching beyond ABO and Rh. Alloimmunization rate was lower in those who began transfusions before 1 year of age, similar to previous studies, supporting the concept of immune tolerance developing in young children who begin transfusions before 1 year of age. Based on our study results, transfusion policies, especially extended antigen matching for Rh and K, should be considered in order to reduce alloimmunization. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Fetal inheritance of GP*Mur causing severe HDFN in an unrecognized case of maternal alloimmunization

The clinical and laboratory features of hemolytic disease of the newborn can be challenging to diagnose during pregnancy in the apparent absence of a blood group antibody. Low-frequency antibodies go undetected due to the lack of appropriate antigen-positive reagent red blood cells (RBCs). A pregnant woman of Southeast Asian descent was referred to a maternal-fetal medicine outpatient clinic due to a complicated obstetric history and a negative antibody screen. This initial visit at 29 weeks and 0 days' gestational age (GA) was unremarkable. A hydropic infant, born at 29 weeks and 5 days' GA, succumbed on the seventh day of life. Comprehensive laboratory testing was performed after birth. The hospital blood bank performed a maternal antibody identification. Direct antiglobulin test was performed on the cord blood. A reference laboratory confirmed an anti-Mia , performed paternal Mia phenotyping, and identified a hybrid glycophorin B-A-B GP*Mur allele. Maternal alloimmunization to low-frequency antigens remains a challenge. Southeast Asians make up a significant percentage in some US locations. Worldwide reports on the frequency of maternal alloimmunization of the MNS system can be used to guide the use of specific reagent RBCs for testing. Such strategies rely on the identification of blood donor units for reagent manufacture and use in perinatal antibody screens. The incidence of Mia and related antibodies is significant among Southeast Asians. In North America, prenatal antibody screening cells are not routinely chosen to match this population. The clinical and societal implications are discussed.

Red Blood Cell Alloimmunization in Transfused Patients With Sickle Cell Disease in Sub-Saharan Africa; a Systematic Review and Meta-Analysis.

Sickle cell disease (SCD) is the most common monogenic disorder in sub-Saharan Africa (SSA). Blood transfusion to increase the oxygen carrying capacity of blood is vital in the management of many patients with SCD. However, red blood cell (RBC) alloimmunization is a major challenge to transfusions in these patients. Commonly in SSA, pretransfusion tests only involve ABO D grouping and compatibility without RBC antibody testing. Data on the frequency of RBC alloimmunization in patients with SCD in SSA are limited. We performed a systematic review and meta-analysis on available data on alloimmunization in transfused patients with SCD to determine the published prevalence of RBC alloimmunization in SCD patients in SSA. Six databases were systematically searched to identify relevant studies, without year or language restrictions. In all, 249 articles were identified and 15 met our selection criteria. The overall proportion of alloimmunization was 7.4 (95% confidence interval: 5.1-10.0) per 100 transfused patients. Antibodies against E, D, C, and K antigens accounted for almost half of antibody specificities, and antibodies to low- and high-frequency antigens were also common and represented almost 30% (20% to low-frequency antigens and 9% to high-frequency antigens) of specificities. Heterogeneity between studies was moderate, and meta-analysis found region of Africa as the major contributor to the heterogeneity. We also observed inconsistencies across studies in reporting of factors that may influence alloimmunization. This review provides an overview of the extent of the alloimmunization problem in SSA and provides a baseline against which to compare the effect of any interventions to reduce the alloimmunization risk.

Prevalence of Anti Erythocyte Alloimmunization to Sub-Saharan African Blood Donors

A part from any incompatible blood transfusion, anti-erythrocyte alloimmunization is observed to pregnant women. It is the result of the passage of red blood cells carrying antigens different from those of the mother during pregnancy and delivery. The Rhesus D system is the most involved; but there are also other systems involved in this alloimmunization. Non-transfusion alloimmunization is an extremely rare event in the order of 1 of 4000 to women in Europe and in most cases concerns the Rhesus D. In sub-Saharan Africa, there are no statistics collected on foeto-maternal alloimmunization. As part of our postgraduate thesis on the sensitization status of red blood cells to acridine, we used the technique of looking for irregular agglutinins. The goal was to find anti-erythrocyte alloimmunization to blood donors in sub-Saharan Africa. We conducted a two-year multicenter prospective and descriptive study of 903 blood donors in Côte d'Ivoire, Benin and Cameroon. The samples were analyzed in the laboratories of the National Blood Transfusion Center of Côte D'Ivoire and Frankfurt according to the technique of the RAI gel card of the BIORAD company after centrifugation and incubation using test red cells treated with S-303. In the case of a positive reaction, identification is made by a panel of red blood cells in the different blood group systems. In our study population, there is a male predominance with a male/female ratio of 7.42. We found a very low prevalence of alloimmunization to non-transfused blood donors (0.9% or 8 cases out of 902). 4 anti-erythrocyte antibodies have been identified (1 Ac anti D and 3 AC anti S); 2 pan-agglutination, 2 unidentified Ac (insufficient serum) and suspicion of anti-glutathione. Anti-erythrocyte alloimmunization to sub-Saharan Africa blood donor is about 0.9% in our series. It remains high compared to European data. This alloimmunization is mainly observed to women with low frequency antigens to black peoples.

The anti-Mia antibody – Report of four cases in a tertiary care hospital with review of literature

Anti – Mia antibody is antibody reacting with Mi III phenotype of the Miltenberger (Mi) subsystem. It is rarely reported in the West, however, it is common in Chinese and South East Asian populations. Very few cases have been reported in India. Here, we report 4 cases of the Anti - Mia antibody picked up on antibody screening of samples (which was performed using Asia ID-Diacell I-II-III Asia (Mia +) 3 cell panel). Patients: In all the four cases, ICT was positive. Antibody screening and Identification was done with 3 cell panel (ID-Diacell I-II-III (Asia)) and 11 cell panel (ID-DiaPanel) respectively. Antibody screening showed reaction in “Asia” cell (carrying Mia Antigen) of 3 cell panel. Antibody identification by 11 cell panel was negative ruling out antibodies of Rh, Kell, Duffy, Kidd, Lewis, P, Lutheran and MNS systems. Reaction with the “Asia” cell suggested the presence of Anti-Mia antibody which was confirmed by obtaining the same result when screening was repeated with 2 different lots of 3 cell panel. Discussion and Conclusion: The Miltenberger (Mi) subsystem comprises of a group of phenotypes of red cells that carry low frequency antigens associated with the MNSs blood group system. The Anti- Mia antibody was first described in 1951 in the serum of Mrs Miltenberger. Anti- Mia antibody is clinically significant and can cause Hemolytic disease of newborn (HDN) and mild to moderate haemolytic transfusion reactions (HTR). Most of the antibody screening and identification panels used in India are imported and represent the Western population. They do not have representation of the Mia antigen on their red cells. This leads to missing out of the Anti- Mia antibody which may cause HDN and HTR leading to significant consequences. Thus, the Mia antigen should be incorporated in our screening panels.

Frequency of Red Blood Cell Antigens According to Parent Ethnicity in Korea Using Molecular Typing.

Frequencies of red blood cell (RBC) blood group antigens differ by ethnicity. Since the number of immigrants is increasing in Korea, RBC antigens should be assessed in children/youths with parents of different ethnicities to ensure safe transfusions. We investigated the frequency of RBC antigens, except for ABO and RhD, in 382 children and youths with parents having Korean and non-Korean ethnicities. Subjects were divided into those with ethnically Korean parents (Korean group; N=252) and those with at least one parent of non-Korean ethnicity (non-Korean group; N=130). The 37 RBC antigens were genotyped using the ID CORE XT system (Progenika Biopharma-Grifols, Bizkaia, Spain). The frequencies of the Rh (E, C, e, hrS, and hrB), Duffy (Fya), MNS (Mia), and Cartwright (Ytb) antigens differed significantly between the two groups. Eight and 11 subjects in the Korean and non-Korean groups, respectively, exhibited negative expression of high-frequency antigens, whereas 14 subjects in the non-Korean group showed positive expression of low-frequency antigens. The frequency of RBC antigens has altered alongside demographic changes in Korea and might lead to changes in distribution of RBC antibodies that cause acute or delayed hemolytic transfusion reaction.

Molecular study of Cw /Cx antigens and frequency of Rh phenotypes in southeast Brazilian blood donors.

The Cw (RH:8), Cx (RH:9), and MAR (RH:51) antigens are encoded by alleles at the Cc locus of the Rh system, where Cw and Cx are considered low-frequency antigens and antithetical to the high-frequency antigen MAR. The frequency of Cw (RH:8) is approximately 2% in Caucasians, 1% in Black people, 4% in Finns, and 9% in Latvians. The aim of this study was to determine the frequency of RhD+ phenotypes in a population of southeast Brazilian blood donors and to perform a molecular study to distinguish the RHCE*Ce.08.01 and RHCE*Ce.09 alleles, responsible for the Cw and Cx expressions, respectively. We investigated 11,536 RhD+ Brazilian blood donors. All samples were phenotyped for D, C, c, E, e, and Cw . In the Cw + samples, a molecular analysis was performed to detect the nucleotide substitutions A122G and G106A, which determine the Cw and Cx antigens, respectively. Cw antigen was found in 110 (0.95%) samples in the following phenotypes: DCw e/dCw e (72/0.62%), DCw e/DCw e (30/0.26%), and DCw e/DCw E (8/0.07%). Among 110 Cw + samples, 108 showed the A122G nucleotide substitution associated with RHCE*Ce.08.01 allele and 2 samples the G106A substitution associated with the RHCE*Ce.09.01 allele. This study showed the prevalence of the RhD+ phenotype in the Brazilian population, and that through the molecular study, it was possible to differentiate the RHCE*Ce.08.01 and RHCE*Ce.09.01 alleles. The phenotype frequency was similar from Black people (1%) and different from Caucasians, Finns, and Latvians.

Sero-prevalence of RBC alloantibodies among Han and minority patients in Xinjiang

The aim of the study was to examine the sero-prevalence and frequency of red blood cell (RBC) alloantibodies (RAAbs) and to investigate the risk factors for producing RAAbs among the Han and Uyghurs in Xinjiang. The RBC antibody screening test and identification were conducted for 45,163 Han and 70,633 Uyghurs admitted to the First Affiliated Hospital of Xinjiang Medical University from October 2010 to December 2014. RBC alloantibodies against the Rh antigens were the most frequent, including anti-E(21.7% in the Han, 21.6% in Uyghurs) and anti-D(18.5% in the Han, 18.2% in Uyghurs). Notably, the sero-prevalence of anti-K and anti-Fy^a was also high in Xinjiang. Transfusion and pregnancy were risk factors among both the Han and Uyghurs; furthermore, Uyghurs had a higher sero-prevalence of RBC antibodies compared to that of Han because of a higher incidence of these risk factors. We concluded that RBC alloantibodies against the Rh factor showed the highest frequency, and antibodies against Asian-related high-frequency antigens, including Fy^a and low-frequency antigens, such as K were notably high in Xinjiang.

A D+ blood donor with a novel RHD*D-CE(5-6)-D gene variant exhibits the low-frequency antigen RH23 (D(W) ) characteristic of the partial DVa phenotype.

Blood donors whose red blood cells (RBCs) exhibit a partial RhD phenotype, lacking some D epitopes, present as D+ in routine screening. Such phenotypes can exhibit low-frequency antigens (LFAs) of clinical significance. The aim of this study was to describe the serologic and genetic profile for a blood donor with an apparent D+ phenotype carrying a variant RHD gene where D Exons 5 and 6 are replaced by RHCE Exon (5-6). Anti-D monoclonal antibodies were used to characterize the presentation of RhD epitopes on the RBCs. RHD exon scanning and DNA sequencing of short- and long-range polymerase chain reaction amplicons were used to determine the RHD structure and sequence. Extended phenotyping for LFAs RH23 (D(W) ) and Rh32 was performed. The donor serology profile was consistent with partial RhD epitope presentation. The donor was hemizygous for an RHD variant allele described as RHD*D-CE(5-6)-D hybrid. The RHCE gene insert is at least 3.868 kb with 5' and 3' breakpoints between IVS4 + 132-c.667 and IVS6 + 1960-IVS6 + 2099, respectively. The sequence for this hybrid was assigned GenBank Accession Number KT099190.2. The RBCs were RH23 (D(W) )+ and Rh32-. A novel RHD*D-CE(5-6)-D hybrid allele encodes a partial RhD epitope and carries the LFA RH23 (D(W) ). This and the epitope profile resemble the partial DVa phenotype. Given that RBCs from this individual lack some RhD epitopes, there is an alloimmunization risk if the donor is exposed to D+ RBCs. Conversely, transfusions of RH23 (D(W) )+ cells to RH23 (D(W) )- recipients also pose an alloimmunization risk.

Frequency of Mi(a) antigen: A pilot study among blood donors.

The Miltenberger (Mi) classes represent a group of phenotypes for red cells that carry low frequency antigens associated with the MNSs blood group system. This pilot study was aimed at determining the Mia antigen positivity in the blood donor population in a tertiary care hospital in New Delhi, India. The study was performed between June to August 2014 on eligible blood donors willing to participate. Antigen typing was performed using monoclonal anti-Mia antiserum by tube technique. Only one of the 1000 blood donors (0.1%) tested was found to be Mia antigen positive. The Mia antigen can, therefore, be considered as being rare in the Indian blood donor population.

Anti-Ula as the Cause of Severe Hemolytic Disease of the Fetus and Newborn: A Case Report

Background: Ula, part of the Kell blood group system, is a low-frequency antigen found predominantly in the Finnish population. Anti-Ula is a rare antibody to cause hemolytic disease of the fetus and newborn (HDFN). Methods and Findings: We report one woman with two pregnancies in which anti-Ula caused severe HDFN requiring intrauterine (IU) transfusions. In the first affected pregnancy, two IU transfusions were performed, but the cause of fetal anemia was unknown at the time and an immune-based mechanism was not suspected. In the following pregnancy, anti-Ula with a titer of 1-2 was identified, and as the fetus was anemic, six IU transfusions were performed. The detection of anti-Ula is difficult, because it is not usually included in the antibody screening cells. Conclusions: The possibility of a rare antibody as the cause of severe HDFN should be kept in mind in cases in which the antibody screening has been negative, and further antibody detection studies should be performed as part of fetal anemia investigations. If anti-Ula is identified in a pregnant woman, close ultrasound monitoring of the fetus is important because HDFN may develop even when the antibody titers are low.

High Percentage of Evanescent Red Cell Antibodies in Patients with Sickle Cell Disease Highlights the Need for a National Antibody Database

Introduction: From 20 to 50% of patients with sickle cell disease are alloimmunized to red cell antigens from transfusions and/or pregnancies. Pre-transfusion testing (e.g. antibody screening) is essential to avoid hemolytic transfusion reactions from clinically significant antibodies, such as those to Rh, Kell, Duffy and Kidd antigens, among others. Unfortunately, alloantibodies may evanesce over time, becoming undetectable or even leading to a negative antibody screen. Furthermore, antibodies to low frequency antigens in the donor pool, mostly from Caucasians, may not be detected because they are not typically expressed on standard reagent red cells used for testing. Both of these facts contribute to the risk of hemolytic transfusion reactions despite negative pre-transfusion screening. To mitigate this risk, individual transfusion services maintain antibody histories of all patients indefinitely, and must refer to them prior to issuing every unit for transfusion.Patients and Methods: We analyzed data collected from the electronic medical records of every adult (19 and older) patient with sickle cell disease who had one or more positive antibody screen in our institution during a 2-year period from 2013-2015 to determine: 1. antibody specificities; 2. percentage of patients with at least one non-reacting alloantibody; 3. specificities of evanescent antibodies; and 4. number (percentage) of patients with antibodies to low frequency antigens.Results: We identified 71 patients, of which 5 were excluded because they only had a cold-reacting anti-M (n=2), anti-Lewis, a warm autoantibody (WAA), or a High Titer Low Avidity (HTLA) antibody (n=1 each). Thus, 66 patients were included in the analysis (62% females). The age range of the study-group was 19-59 years old (mean ± SD, 33 ± 11 years), similar between males and females (p = 0.43). Males tended to have an antibody screen ordered more often during the study-period, with a trend toward statistical significance (9.4 versus 5.0 times; p = 0.06). The total number of clinically significant alloantibodies was 218 with mean and median number per patient of 3.3 and 3.0, respectively. In addition, 16 patients also had a WAA. Anti-E was the most common alloantibody, followed by anti-C and anti-K; the table shows the antibodies identified at least once in 10% or more of the patients, as well as how often they were not reacting. Of 9 patients with anti-D, 7 were Rh positive, consistent with the propensity of African-Americans to express a D variant. Of note, 30 patients (45%) had antibodies to one or more low frequency antigen such as Cw, V, Vs, Goa, Jsa, Kpa, Lutheran b, Wra, and Ytb; 6 patients (9%) only had alloantibody(ies) to these antigens. Only 12 patients had a positive antibody screen every time they were tested. However, they had significantly fewer tests (average and median of 2, range of 1-6) compared with 54 patients with at least one antibody screen completely negative (average and median of 5 tests, range of 1-30) (p < 0.0001). Table 1Rh systemKellDuffyKiddMNSsOtherAntibody specificityDCEVGoaKJsaFyaFybJkbSAUSNumber of patients93040147201518912177Percentage of total antibodies4%14%18%6%3%9%7%8%4%5%8%3%Times not reacting516218312121078123Percent evanescent56%53%53%57%43%60%80%56%78%67%71%43%AUS-antibody of unknown specificity; Fya-Duffy a; Fyb-Duffy b; Jkb-Kidd b;Conclusions: Our results demonstrate that 81% of patients with sickle cell disease with a history of red cell alloantibodies had at least one test in which the antibody was not detectable. Delayed hemolytic transfusion reactions are the major risk of evanescent alloantibodies not known to the transfusion service preparing the units. Such reactions may even be fatal, especially if not promptly recognized, since they may be confused with a pain crisis. In addition, we noticed that almost half of the patients had antibodies to low frequency antigens that could have been missed during pre-transfusion testing. Considering that patients with sickle cell disease often suffer from lack of continuity of care, unawareness of their antibody history may lead to life-threatening transfusion reactions. We suggest that a national, or even regional, database of red cell alloimmunization in this patient population is warranted for increased transfusion safety. DisclosuresNo relevant conflicts of interest to declare.

A Case of Hemolytic Disease of the Newborn due to Di (a) Antibody.

Anti-Dia is a clinically significant red cell antibody known to cause hemolytic disease of the newborn. Here, we report on a case of mild hemolytic disease of the newborn caused by Dia antibody. The mother had three prior pregnancies with no history of blood transfusion. She delivered a preterm 35-week-old female newborn by cesarean section. The neonate developed anemia and mild icterus on postnatal day five with hemoglobin of 9500 mg/dL and total bilirubin of 10 mg/dL. The direct antiglobulin test on the neonate's red blood cells was positive. The maternal serum and an eluate from the infant RBCs were negative in routine antibody detection tests but were positive using commercially prepared Di(a+) red cells. The neonate was discharged home in stable condition following treatment with erythropoietin and phototherapy. When a newborn has a positive DAT in the absence of major blood group incompatibility or commonly detected RBC antibodies, an antibody to a low frequency antigen such as Dia must be considered. Further immunohematology tests are required to determine presence of the antibody and the clinician must be alerted to closely monitor the infant for signs of anemia and hemolysis.