Adsorption and elution study detected misidentification of para-Bombay phenotype donor in an incompatible crossmatch with Bombay phenotype patient.

Bombay and para-Bombay are rare phenotypes with H antigen-deficient red blood cells. A 54-year-old male patient suffering from suspected malignant pleural effusion was planned for thoracotomy. The patient's blood group showed blood group discrepancy during pretransfusion testing due to ABO isoagglutinin. Further workup with anti-H lectin was negative with pan-reactive antibody screening and negative autocontrol, which suggested that the patient is Bombay RhD positive. A known Bombay phenotype donor was called for donation. That Bombay donor is a para-Bombay donor incorrectly labeled as Bombay in another hospital. During pretransfusion testing, there was an incompatible crossmatch. Hence, the adsorption of donor red cells with the patient's serum was performed, followed by heat elution. The eluate was pan-reactive with an antibody screening panel indicating anti-H present. The Lewis phenotype of the donor is Leb positive, which reflects the secretor status of the individual. This case highlights the importance of reverse grouping, adsorption, Lewis phenotyping, and elution testing in detecting and differentiating Bombay and para-Bombay phenotypes to avoid fatal adverse transfusion events.