The AFP assay is a two-step “sandwich” type assay in which two monoclonal mouse antibodies, directed against two different epitopes of the molecule, are employed.
The samples or calibrators are first incubated in tubes coated with the first monoclonal antibody. The contents of the tubes are then aspirated and the presence of AFP in the sample is revealed by incubation with the second, 125I labelled antibody. The contents of the tubes are aspirated and the bound radioactivity is determined in a gamma counter.
The AFP concentrations in the samples are obtained by interpolation from the standard curve. The concentration of AFP in the samples is directly proportional to the radioactivity.