Blood group discrepancy in A_h 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.