The technology uses two high affinity monoclonal antibodies in an immunoradiometric assay (IRMA) system.

The 125I labelled signal-antibody binds to an epitope of the free PSA molecule spatially different from that recognized by the biotincapture- antibody. The two antibodies react simultaneously with the antigen present in standards or samples, which leads to the formation of a capture antibody - antigen - signal antibody complex, also referred to as a “sandwich”. During a 2-hour incubation period with shaking immuno-complex is immobilized to the reactive surface of streptavidin coated test tubes. Reaction mixture is then discarded, test tubes washed exhaustively, and the radioactivity is measured in a gamma counter.

The concentration of antigen is directly proportional to the radioactivity measured in test tubes.

By constructing a calibration curve plotting binding values against a series of calibrators containing known amount of free PSA, the unknown concentration of free PSA in patient samples can determined.

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