Neonatal testing leading to the identification of B_h (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+.