Immunohematologic aspects of alloimmunization and alloantibody detection: A focus on pregnancy and hemolytic disease of the fetus and newborn

The selection and preparation of red cell components for intrauterine transfusion: A national survey

BACKGROUND AND OBJECTIVES

The practice regarding the selection and preparation of red blood cells (RBCs) for intrauterine transfusion (IUT) is variable reflecting historical practice and expert opinion rather than evidence-based recommendations. The aim of this survey was to assess Canadian hospital blood bank practice with respect to red cell IUT.

MATERIALS AND METHODS

A survey was sent to nine hospital laboratories known to perform red cell IUT. Questions regarding component selection, processing, foetal pre-transfusion testing, transfusion administration, documentation and traceability were assessed.

RESULTS

The median annual number of IUTs performed in Canada was 109 (interquartile range, 103-118). RBC selection criteria included allogeneic, Cytomegalovirus seronegative, irradiated, fresh units with most sites preferentially providing HbS negative, group O, RhD negative, Kell negative and units lacking the corresponding maternal antibody without extended matching to the maternal phenotype. Red cell processing varied with respect to target haematocrit, use of saline reconstitution (n = 4), use of an automated procedure for red cell concentration (n = 1) and incorporation of a wash step (n = 2). Foetal pre-transfusion testing uniformly included haemoglobin measurement, but additional serologic testing varied. A variety of strategies were used to link the IUT event to the neonate post-delivery, including the creation of a unique foetal blood bank identifier at three sites.

CONCLUSION

This survey reviews current practice and highlights the need for standardized national guidelines regarding the selection and preparation of RBCs for IUT. This study has prompted a re-examination of priorities for RBC selection for IUT and highlighted strategies for transfusion traceability in this unique setting.

Antibody-mediated antigen loss switches augmented immunity to antibody-mediated immunosuppression

Antibodies against fetal red blood cell (RBC) antigens can cause hemolytic disease of the fetus and newborn (HDFN). Reductions in HDFN due to anti-RhD antibodies have been achieved through use of Rh immune globulin (RhIg), a polyclonal antibody preparation that causes antibody-mediated immunosuppression (AMIS), thereby preventing maternal immune responses against fetal RBCs. Despite the success of RhIg, it is only effective against 1 alloantigen. The lack of similar interventions that mitigate immune responses toward other RBC alloantigens reflects an incomplete understanding of AMIS mechanisms. AMIS has been previously attributed to rapid antibody-mediated RBC removal, resulting in B-cell ignorance of the RBC alloantigen. However, our data demonstrate that antibody-mediated RBC removal can enhance de novo alloimmunization. In contrast, inclusion of antibodies that possess the ability to rapidly remove the target antigen in the absence of detectable RBC clearance can convert an augmented antibody response to AMIS. These results suggest that the ability of antibodies to remove target antigens from the RBC surface can trigger AMIS in situations in which enhanced immunity may otherwise occur. In doing so, these results hold promise in identifying key antibody characteristics that can drive AMIS, thereby facilitating the design of AMIS approaches toward other RBC antigens to eliminate all forms of HDFN.

Immunohematological testing and transfusion management of the prenatal patient

The primary indication for immunohematological testing in the prenatal patient is to detect and identify maternal red cell antibodies. If there are antibodies that are expected to hemolyze the fetus' red cells, their strength of reactivity must be tested, and the fetus' antigen status determined. After delivery, testing is performed to assess the extent of fetomaternal hemorrhage, as a large hemorrhage may require other therapeutic interventions. Another major role for immunohematological testing is to select blood components appropriately when intrauterine transfusion is required for fetal anemia resulting from maternal alloimmunization or some other cause. Supplementation with molecular methods has transformed the practice of immunohematology, particularly as it applies to typing for the D antigen of the Rh blood group system. Notwithstanding the advances in testing, close coordination and communication between the transfusion service and the obstetrics service are the foundation for ensuring the finest care for prenatal patients, and for new mothers and their infants. This review describes testing and transfusion practices for prenatal patients, using case presentations to highlight the management of selected immunohematological findings. It also includes a discussion of key patient management topics that are currently unresolved.

Alloimmunization to Rh Antigen (D, C, E, C, E) Among Pregnant Women Attending Antenatal Care in South Western Uganda

INTRODUCTION

Maternal red cell alloimmunization to Rh antigen in pregnant women occurs when the immune system is sensitized by foreign red blood cell surface antigens, in this case fetal red blood cells, inducing an immune response. Various antigens of blood group systems may cause alloimmunization, especially the Rh, Kel, Fy, JK, and MNS systems. This study aimed to determine alloimmunization to the different frequencies of Rh antigen among pregnant women in South Western Uganda.

METHODS

A total of 1369 pregnant women consented and were recruited into a cross-sectional study during their regular antenatal visits during the period August 2020 to July 2021. Samples (4 mL) of anticoagulated and coagulated blood were obtained, and Rh blood grouping including Rh antigen and the indirect antiglobulin test (IAT) was carried out using the agglutination technology of the LISS ID-Card technique in the Ortho Biovue ID-Micro Typing System.

RESULTS

Out of 1369 participants recruited to the study, 78 (5.7%) were D-, 1291 were D+, and 134 (9.8%) had alloantibodies. Among those with alloantibodies, 115 (85.8%) were D+ and 19 (14.2%) D-. The percentage alloimmunization according to the Rh antigens was highest in e (9.72%), c (2.48%), C (2.34%) and E (0.94%) antigens. With the ABO system, alloimmunization was highest in blood group B (10.7%), followed by A (10.6%), O (9.2%) and then AB (7.1%). Alloimmunization was more prevalent in D- (24%) than in D+ participants (8.9%). Rhesus antigen e was the most prevalent antigen (99.8%), followed by c. The alloimmunization rate of 9.8% among these participants is high, and appears in both D+ and D- women. The other Rhesus antigens are seen to cause alloimmunization, with antigen e causing the highest prevalence. In conclusion, there is a need to identify antibodies and study the outcome for clinical significance, especially in D+ women, to facilitate proper pregnancy management.

ABO and Rh Antigen Distribution Among Pregnant Women in South Western Uganda

Introduction

ABO and Rh are the major blood group systems in Transfusion Medicine, the ABO system based on two red cell antigens (A, B) while the Rh has about 50 antigens of which five are highly clinically significant (D, C, c, E, e). These vary among races and ethnic groups. Blood type phenotype incompatibility between mother and fetus may result in antigen mismatch, triggering alloimmunization, and thus causing hemolytic transfusion reaction (HTR), which results in hemolytic disease of fetus and newborn (HDFN). This study aimed to determine the frequencies of ABO and rhesus blood group antigen in the pregnant women in South Western Uganda.

Methods

A cross-sectional study was carried out on 1369 pregnant women who were recruited and provided consent to participate during their regular antenatal visits between August 2020 and July 2021. Four milliliters (4mL) of EDTA-anti-coagulated blood samples were collected and ABO and Rh-blood grouping including Rh antigen screening was done using the agglutination technology comprised of glass beads and reagent contained in a column of the Ortho Biovue ID Micro Typing System (Ortho Clinical Diagnostics, New Jersey, USA). The Rh antigen phenotypes and frequencies were then determined.

Results

There was percentage distribution of 99.8%, c 99.3%, D 94.3%, C 19.2% and E 15.9%, with Rh cDe/cDe (65.1%) being the most common phenotype followed by cDe/CDe (15%), cDe/cDE (10.8%) and cDE/cDE 0.1% least common. The ABO grouping frequency was obtained as O 49.4%, A 29.5%, B 17.0% and AB 4.1%, with D positivity at 94.3%.

Discussion

Population genetic variations result in varied expressions of red cell antigens that may have clinical complications. Knowledge of the presence of these Rh antigen distributions and phenotype frequencies during pregnancy help in rational management of the pregnancy, alloimmunization and better approach to safe blood transfusion.

Noninvasive diagnostics of fetal KEL*01.01 allele from maternal plasma of immunized women using digital PCR protocols

Allo-antibodies produced by K-negative pregnant women against a fetal K antigen from the Kell blood group system may cause hemolytic disease of the fetus and newborn (HDFN). Predicting the fetal K antigen using noninvasive prenatal testing (NIPT) is important for decisions concerning management of pregnancies. Digital and droplet digital PCR techniques permit the detection of fetal single nucleotide variant with a higher specificity and sensitivity than real-time polymerase chain reaction (PCR).

AIM

The aim was to evaluate and compare protocols for fetal KEL*01.01 genotyping using different assays and digital PCR platforms.

METHODS

DNA isolated from 59 pregnant women (9-39 weeks of gestation, 49 with anti-K) was tested using home-made and custom-ordered KEL*01.01/KEL*02 assays with Droplet Digital™ and QuantStudio™3D. The results were compared with fetal/neonatal genotypes/phenotypes.

RESULTS

Fetal KEL*01.01 results using all tested protocols were concordant with fetal/neonatal KEL*01.01 genotypes/phenotypes. None of the tested combinations of assays or digital PCR platforms gave false KEL*01.01-negative results, but inconclusive KEL*01.01 reads were observed in all tested protocols. For 36 cases compared using two digital PCR platforms and assays, there were not statistically significant differences in a level of fetal KEL*01.01 fraction (p < .72).

CONCLUSION

Independent of the applied dPCR and ddPCR platforms and KEL*01.01 assays, prediction of the fetal KEL*01.01 is highly reliable. Before implementation in routine practice further validation of the KEL*01.01 protocol with a larger group of pregnant women should be performed.

Hemolytic Disease of the Newborn: A Review of Current Trends and Prospects

Hemolytic disease of the newborn (HDN), also known as Erythroblastosis fetalis, is a hemolytic condition that predominantly affects rhesus-positive fetuses and infants born to rhesus-negative mothers. The pathophysiology of HDN begins with maternal antibodies attacking fetal red blood cells following alloimmunization due to rhesus or ABO incompatibility between the maternal and fetal blood. Previously, HDN was known to cause fetal death in 1% of all pregnancies, but with the advent of immunoprophylactic therapies, the condition can be currently fairly well managed with fewer complications if diagnosed early. Diagnosis calls for extensive history taking, physical examination, serological studies, and imaging modalities such as pelvic ultrasound scans. To prevent the disease, earlier intravenous immunoglobulin (IVIG) should be given to pregnant Rh- women who have not been sensitized. It is also vital to understand prospective complications such as severe hyperbilirubinemia and develop appropriate remedies. Because of its great incidence and nature, HDN has been thoroughly explored, and more studies are being conducted each year, revealing new insights about the condition. This review covers the disorder's etiology, diagnosis, and management, including the most current findings as of 2021, as well as trends and prospects, to help in future research and evidence-based medical practice.