A two-site immunoradiometric assay for human pregnancy-associated plasma protein A (PAPP-A) using monoclonal antibodies

A rapid, sensitive immunoradiometric assay has been developed for human pregnancy-associated plasma protein A (PAPP-A) using a purified mouse monoclonal antibody as the tracer and a rabbit polyclonal antibody to this protein in the solid-phase antibody preparation. The assay showed no measurable cross-reaction (< 0.1%) against a range of purified human placental proteins, and a good correlation with a previously described radioimmunoassay procedure when tested on samples taken throughout normal human pregnancies. No PAPP-A-like immunological activity could be detected in sera from non-pregnant women, confirming the absence of this protein from the circulation outside pregnancy.