Comparison Of Highly Sensitive Sandwich Enzyme Immunoassay And Radioimmunoassay For Human Ferritin

A highly sensitive sandwich enzyme immunoassay (EIA) for human ferritin was developed using rabbit anti-ferritin IgG-coated polystyrene balls and affinity-purified rabbit anti-ferritin Fab' labelled with β-D-galactosidase from Escherichia coli and compared with the corresponding sandwich radioimmuno assay (RIA). The specific and nonspecific binding of labelled anti-ferritin to the polystyrene balls were examined in relation to the amount of labelled anti-ferritin used per tube, and the highest sensitivity of each immunoassay (0.2 amol/tube in EIA and 2.5 amol/tube in RIA) was obtained by using the minimal amount of the corresponding labelled anti-ferritin (0.71 fmol in EIA and 4.5 fmol=4436 cpm in RIA) which gave a reliable calibration curve. The sandwich RIA was less sensitive, largely because the specific radioactivity of 125I-labelled anti-ferritin used was not sufficiently high.