Detection of Rh antibodies in patient plasma using iRBCs and gel column agglutination. (A-E) Plasma containing (A) anti-D, (B) anti-C, (C) anti-c, (D) anti-E, and (E) anti-e were tested against a panel of control dRBCs and ficin-treated iRBCs or esRBCs. Each assay included control dRBCs expressing or lacking the corresponding Rh antigen (left) along with Rh null and D-- iRBCs, and iRBCs/esRBCs negative or positive for the corresponding Rh antigen (right). Agglutination prevents cells from traveling through the gel matrix to the bottom of each column upon centrifugation and indicates the presence of antibody in the plasma sample.