Five coupling concentrations of capture antibody (0.2, 1, 5, 10 and 20 μg/ml) were incubated with serial dilutions of CA125 antigen in the assay diluent. The captured antigen was detected by 1 μg/ml of biotinylated detection antibody. A: RDI antibodies, X306 capture, X52 detection; B: FDI antibodies, M11 capture, OC-125 detection; C–D: FIII antibodies, C: M002201 capture, M002203 detection; D, orientation 1: M8072320 capture, M8072321 detection; orientation 2: M8072321 capture, M8072320 detection.