A novel observation on grouping anomaly: The phenomena mimicking the Bel genetic variant of the ABO blood groups

Abstract

Background: Discrepancy in “forward/reverse” grouping leads to confusion in assigning ABO group to a person. It could be genetic in nature and classified according to the presence/absent of antigen on red blood cell (RBC) vis-a-vis corresponding alloantibody in plasma. AIM: The aim of the study was to investigate the grouping anomaly found in a recently delivered woman who required transfusion. Materials and Methods: A standard protocol for investigation was followed. Results: A 27-year-old female, gravida 4, para 3, was grouped O on forward grouping, but her serum did not agglutinate Group B RBCs tested. Absorption-elution study gave an active eluate from her sensitized RBCs with anti-B or anti-A+B. Saliva showed H, but no B antigens indicating to her Bel phenotype. However, 2-week latter in the follow-up study, her serum revealed a presence of complement binding high titer anti-B. The problem of missing anti-B on the previous occasion was attributed to hemagglutination inhibition caused by accumulated complement macromolecules on RBCs that gave rise to physical hindrance in the formation hemagglutination clumps. Conclusion: The unusual case of erroneous reversed grouping was attributed to complement-mediated hemagglutination inhibition. The positive eluate obtained from sensitized RBCs of the mother was considered to be due to a contamination of fetal RBCs in maternal circulation entered during her postpartum phase of pregnancy. It could also be due to a conversion of H to B antigen no matter in trace amount by the fetal B group-specific transferase percolated into maternal circulation.

Keywords

• anomalous abo group
• complement-mediated hemaggltination inhibition
• mimicking bel phenotype