Anti-f with anti-c detected during pre-transfusion testing: A diagnostic challenge.

The Rh blood group system includes several compound antigens, among which the f antigen (ISBT 004006) is expressed when the c and e antigens occur in cis position on the same RhCE protein. Anti-f is a rare alloantibody but is clinically significant due to its potential to cause hemolytic transfusion reactions and hemolytic disease of the newborn. We report a rare case of anti-f with coexisting anti-c identified during pre-transfusion testing in a 40-year-old female admitted for elective hysterectomy. Her blood group was O Rh D positive and her antibody screen was positive with a negative autocontrol and direct antiglobulin test. Extended phenotyping revealed CCee, K-negative phenotype. Antibody identification using an 11-cell panel suggested anti-c and anti-f, which was further confirmed by allogeneic adsorption studies using Rh-phenotyped donor cells. During cross-matching, only R1R1 units were found to be compatible. This case highlights the importance of extended Rh phenotyping, adsorption studies, and careful selection of compatible donor units in resolving rare Rh antibody combinations to ensure safe transfusions to patients.