AB para-Bombay phenotype: a rare blood group variant and its clinical significance

Investigating ABO Blood Groups and Secretor Status in Relation to SARS-CoV-2 Infection and COVID-19 Severity

The ABO blood groups, Lewis antigens, and secretor systems are important components of transfusion medicine. These interconnected systems have been also shown to be associated with differing susceptibility to bacterial and viral infections, likely as the result of selection over the course of evolution and the constant tug of war between humans and infectious microbes. This comprehensive narrative review aimed to explore the literature and to present the current state of knowledge on reported associations of the ABO, Lewis, and secretor blood groups with SARS-CoV-2 infection and COVID-19 severity. Our main finding was that the A blood group may be associated with increased susceptibility to SARS-CoV-2 infection, and possibly also with increased disease severity and overall mortality. The proposed pathophysiological pathways explaining this potential association include antibody-mediated mechanisms and increased thrombotic risk amongst blood group A individuals, in addition to altered inflammatory cytokine expression profiles. Preliminary evidence does not support the association between ABO blood groups and COVID-19 vaccine response, or the risk of developing long COVID. Even though the emergency state of the pandemic is over, further research is needed especially in this area since tens of millions of people worldwide suffer from lingering COVID-19 symptoms.

Genotyping of the rare Para-Bombay blood group in southern Thailand

INTRODUCTION

The para-Bombay phenotype, or H-deficient secretor, results from different mutations of the FUT1, with or without the FUT2 mutation. Consequently, there is an absent or weak expression of the H antigen on red blood cells (RBCs). Routine ABO blood grouping for two siblings with blood group O showed discrepant results with their parental blood group AB. Fragments encompassing the entire coding region of the FUT1 and FUT2 genes were investigated.

METHODS

Blood and saliva specimens were collected to verify the correct ABO grouping by cell grouping, serum grouping and the hemagglutination inhibition (HI) test, respectively. The FUT1 and FUT2 genomes were identified using the whole-exome sequencing (WES) in two children's DNA blood specimens and may have caused, or been relative to, their blood group. Genetic variations of the FUT1 and FUT2 genes have been investigated in the other family members using the Sanger sequencing.

RESULTS

The serologic reaction results of the proband revealed that A, B and H antigens were absent on RBCs, and that the serum contained anti-H. However, ABH and AH antigens were present in the saliva PB1 and PB2, respectively. The probands PB1 and PB2 were assigned as AB and A blood groups, respectively. Blood genotyping confirmed that heterozygous mutations of the FUT1 gene, c.551_552delAG, were identified. Three family members, PB3, PB, and PB8, also showed normal ABO blood groups, but their genotypes were also the FUT1 mutation c.551_552delAG.

CONCLUSIONS

The FUT1 mutation c.551_552delAG may result in the reduced or absent H antigen production on RBCs, which characterizes the para-Bombay phenotypes. Blood genotyping is essential if these individuals need a blood transfusion or are planning to donate blood.

Prevalence of adsorbed A antigen onto donor-derived group O red cells in children following stem cell transplantation: A single-centre evaluation

BACKGROUND AND OBJECTIVES

A group AB D-positive child presented 1 year after haematopoietic stem cell transplant (HSCT) from a group O D-negative donor as group A D-negative. Engraftment remained at 100% in white cell lineages. The reason for the unusual result was explored, and the scarcely reported phenomenon of adsorption of secreted antigen was considered. This study also investigated the prevalence of secreted antigen adsorbed onto donor-derived group O red blood cells (RBCs) in children after HSCT and defined a process for laboratory management.

MATERIALS AND METHODS

Retrospective data analysis of HSCTs carried out over 19 months at Great Ormond Street Hospital was conducted to identify cases of adsorbed A antigen after HSCT. Investigation of RBC reactions with different clones of anti-A and in vitro experiments was performed to recreate adsorption.

RESULTS

Nineteen A to O HSCTs were conducted over 19 months, of which six (31%) displayed weak A antigen on RBCs despite full myeloid engraftment. Negative reactions with anti-A were obtained when run on an alternative clone. Laboratory protocols for the future management of these cases have been developed.

CONCLUSION

Passive adsorption of secreted antigen is responsible for these results and is more widespread than previously reported, as a third of A to O HSCTs at our centre demonstrated this phenomenon. A process has been implemented into the laboratory to manage this cohort, ensuring component groups compatible with both donor and recipient are given, and the shared care centres are aware of these requirements.

Incidental Discovery of a Patient with the Bombay Phenotype

Bombay phenotype, an exceptionally rare blood type in individuals outside of Southeast Asia, occurs in approximately 1 in 1,000,000 individuals in Europe. This blood phenotype is characterized by the absence of the H antigen on red blood cells (RBCs) and in secretions. As the H antigen is the structure on which the ABO system is built, individuals lacking this antigen are unable to produce A or B antigens and appear as type O on routine ABO phenotyping. H deficiency does not cause ill effect; however, these individuals produce an anti-H alloantibody capable of causing severe acute hemolytic transfusion reactions when exposed to RBCs that express the H antigen. In this case study, we highlight the incidental discovery of a patient with Bombay phenotype in a North American hospital system, expected test results, the immunologic and genetic basis underlying the Bombay and para-Bombay phenotypes, and methods to ensure availability of compatible blood.

Blood group discrepancy in Ah para-Bombay phenotype: a rare blood group variant and its clinical significance

Individuals with the rare para-Bombay phenotype have inherited defects in producing H associated with FUT1 and/or FUT2 genes. We report a case of blood group discrepancy in a para-Bombay patient from a tertiary care hospital of eastern India. A 31-year-old woman with rheumatic heart disease presented with fatigue and breathlessness and was then scheduled for valvuloplasty, for which a blood transfusion request was sent to the blood center. During pre-transfusion testing, red blood cell (RBC) testing showed group O, and serum testing showed strong reactivity with group B RBCs, weak reactivity with group O RBCs, and very weak reactivity with group A RBCs. Saliva inhibition testing and enzyme treatment of RBCs concluded the patient to be of "A_h para-Bombay" phenotype. The patient's Lewis phenotype was Le(a-b+). This patient's serum also had cold-reacting anti-IH along with anti-B. This case report highlights the importance of performing an advanced immunohematologic workup, including adsorption, elution, enzyme treatment, and saliva inhibition testing for identification of weak A or B subgroups as well as the rare para-Bombay blood group, when routine ABO typing, using forward and reverse grouping, is inconclusive. Accurate identification of blood group helps in preventing transfusion-related adverse events and encouraging safe transfusion practice.

Individuals with the rare para-Bombay phenotype have inherited defects in producing H associated with FUT1 and/or FUT2 genes. We report a case of blood group discrepancy in a para-Bombay patient from a tertiary care hospital of eastern India. A 31-year-old woman with rheumatic heart disease presented with fatigue and breathlessness and was then scheduled for valvuloplasty, for which a blood transfusion request was sent to the blood center. During pre-transfusion testing, red blood cell (RBC) testing showed group O, and serum testing showed strong reactivity with group B RBCs, weak reactivity with group O RBCs, and very weak reactivity with group A RBCs. Saliva inhibition testing and enzyme treatment of RBCs concluded the patient to be of “A_h para-Bombay” phenotype. The patient’s Lewis phenotype was Le(a–b+). This patient’s serum also had cold-reacting anti-IH along with anti-B. This case report highlights the importance of performing an advanced immunohematologic workup, including adsorption, elution, enzyme treatment, and saliva inhibition testing for identification of weak A or B subgroups as well as the rare para-Bombay blood group, when routine ABO typing, using forward and reverse grouping, is inconclusive. Accurate identification of blood group helps in preventing transfusion-related adverse events and encouraging safe transfusion practice.

Neonatal testing leading to the identification of Bh (para-Bombay) phenotype in the mother: case report with review of the literature

Para-Bombay is a rare phenotype with a homozygous nonfunctional FUT1 gene and a normal FUT2 gene leading to H-deficient red blood cells (RBCs) with or without ABH substances, depending on inheritance of the ABO gene. This case is about a 5-day-old male baby suffering from sepsis who required a 45-mL packed RBC transfusion. The baby's sample tested as A₁B, D+ and mother's sample tested as group O, D+ with group 4 discrepancy due to ABO isoagglutinins. Further workup of the mother's sample with anti-H lectin was negative, which suggested the mother to be group O_h, D+. Antibody screening was panreactive with negative autocontrol, suggestive of anti-H. The titer of immunoglobulin (Ig)M anti-H was 64, IgG titer using dithiothreitol was 8, and anti-IH was absent. A negative adsorption and elution test suggested that RBCs were devoid of A and B antigens. The father's sample tested clearly as group A₁, D+; hence, the cis-AB blood group was ruled out in the baby. The secretor study of the mother's saliva revealed the presence of B and H substances that neutralized polyclonal B and H antisera. Therefore, we concluded that the mother was of the para-Bombay (B_h) phenotype. This case highlights the importance of reverse grouping and resolving blood grouping discrepancies between mother and child-in this case because of an incongruous ABO blood type of the baby and the mother who was previously tested as group O, D+.

Para-Bombay is a rare phenotype with a homozygous nonfunctional FUT1 gene and a normal FUT2 gene leading to H-deficient red blood cells (RBCs) with or without ABH substances, depending on inheritance of the ABO gene. This case is about a 5-day-old male baby suffering from sepsis who required a 45-mL packed RBC transfusion. The baby’s sample tested as A₁B, D+ and mother’s sample tested as group O, D+ with group 4 discrepancy due to ABO isoagglutinins. Further workup of the mother’s sample with anti-H lectin was negative, which suggested the mother to be group O_h, D+. Antibody screening was panreactive with negative autocontrol, suggestive of anti-H. The titer of immunoglobulin (Ig)M anti-H was 64, IgG titer using dithiothreitol was 8, and anti-IH was absent. A negative adsorption and elution test suggested that RBCs were devoid of A and B antigens. The father’s sample tested clearly as group A₁, D+; hence, the cis-AB blood group was ruled out in the baby. The secretor study of the mother’s saliva revealed the presence of B and H substances that neutralized polyclonal B and H antisera. Therefore, we concluded that the mother was of the para-Bombay (B_h) phenotype. This case highlights the importance of reverse grouping and resolving blood grouping discrepancies between mother and child―in this case because of an incongruous ABO blood type of the baby and the mother who was previously tested as group O, D+.

Transfusion practice blind spot in para-Bombay: A case report

H-deficient phenotype individuals with absent or weak anti-H activity may remain undetected on standard routine blood grouping. We report a case of a 59-year-old-man presented with symptomatic anaemia secondary to upper gastrointestinal bleed with haemoglobin level of 68 g/L who required two units of packed red blood cells. He was previously grouped as O Rh D positive and had a history of uneventful multiple blood transfusions. His latest pre-transfusion investigations showed ABO discrepancy between forward and reverse blood grouping, pan-agglutination in both antibody screening and identification with negative direct Coombs test and autocontrol. Further testing including anti-H lectin test and saliva secretor study confirmed that the patient blood group was para-Bombay B RhD positive. This case highlights that the para-Bombay phenotype can be mistakenly labelled as "O" if further investigations are not performed.