iRBCs identify antibodies against high-prevalence or low-prevalence Rh antigens in patient plasma. (A-B) Patient plasma containing antibody against (A) the high-prevalence antigen hr^S or (B) low-prevalence antigens V or Go^a were tested against a panel of control dRBCs and ficin-treated iRBCs. Each assay included the 3 control dRBCs routinely used for antibody screening: DCe (R1R1), DcE (R2R2), and ce (rr) phenotypes (left). In panel A, iRBCs that were Rh null, D--, e⁺ hr^S− hr^B+, and e⁺ hr^S+ hr^B− were selected to show hr^S specificity (right). In panel B, patient plasma was tested against iRBCs that were Rh null, D--, or expressing low-prevalence Go^a, DAK, or VVS antigens. Agglutination of cells prevents them from traveling through the gel matrix to the bottom of each column upon centrifugation and indicates the presence of antibody in the plasma sample.