Background/Case Studies: The detection of clinically significant antibodies is a critical step in pre-transfusion testing. It helps uncover antibodies to blood group antigens, other than those of the ABO blood group system, which may otherwise result in an incompatible transfusion. Further measures to identify specificity of antibodies detected and the provision of antigen-negative blood where necessary, help in prevention of hemolytic transfusion reactions.
The prevalence of antigens and detection of their corresponding antibodies to variant hybrid glycophorins, of the MNS blood group system, often require the inclusion of Mia (MNS7) antigen when screening for antibodies in countries within Southeast and East Asia. Antibodies found reacting consistently towards known Mia+ phenotype red cells, are often reported as ‘anti-Mia’.
As the most commonly encountered antibody in Singapore, detection and identification of anti-Mia is usually straightforward, especially when Mia+ red cell reagents used are of the more prevalent Gp.Mur phenotype. Incidental inclusion of Gp.Bun phenotype in several hospital antibody screening panels (ID-DiaCell I, II, III Asia, Biorad, Switzerland) however, led to the detection of an apparent antibody to a blood group antigen of low prevalence. The specificity of this antibody was later concluded as anti-Hop as the most probable antibody, after confirmation of the Gp.Bun phenotype with the manufacturer.
This incident created a unique opportunity to evaluate the prevalence and clinical significance of anti-Hop, as well as frequency of Gp.Bun and/or Gp.Hop phenotype in Singapore.
Study
Design/Methods: This study involved three components: (1) screening 1,000 Singaporean donors using in-house anti-Mia reagents via column agglutination; Mia+ cells were further tested with in-house polyclonal anti-Hop to identify Gp.Bun/Hop-positive cells for Monocyte Monolayer Assay (MMA), (2) retrospective analysis of anti-Hop prevalence in two hospitals, and (3) performing MMA with Gp.Bun/Hop-positive red cells sensitized with 2 anti-Hop examples. Monocyte reactivity (%) was then quantified and Interpreted.
Results/Findings: Among 1,000 donors, 12 (1.2%) were identified as Hop+. Donors with Gp.Bun/Hop phenotype were primarily Chinese (91.6%) and Malay (8.3%). Chi-square analysis showed significant correlation between Gp.Bun cell availability and anti-Hop detection (p=0.0001). Anti-Hop was concluded for 37 (1.0%) patients from 3699, all of whom were Chinese. MMA was interpreted as negative with Monocyte reactivity between 0.3% to 2.1%.
Conclusions: Although the study was able to provide insights to low clinical outcomes of anti-Hop, attempts to further study and differentiate antibodies of related specificities are often challenged with the lack of phenotyped resources or specialized tests.
