A Monoclonal Antibody-Based Immunoradiometric Assay for Low Molecular Weight Insulin-Like Growth Factor Binding Protein/Placental Protein 12

Abstract
We describe a sensitive immunoradiometric assay for insulin-like growth factor binding protein/Placental Protein 12 (IGF-BP/PP12) using monoclonal antibodies. This assay has a detection limit of 0.25 μg/l IGF-BP/PP12. Parallel dose response curves were obtained with purified IGF-BP/PP12, amniotic fluid, decidual cytosol extract, and serum. The assay is reproducible (intra-assay variation 4.3–8.2% and interassay variation 9.7–11.1%) and fast (< 5 hours). A crossreactivity of less than 0.01% for all other proteins tested reflects high specificity. Using this method the mean serum IGF-BP/PP12 concentration in healthy women was 5.2 μg/l. During pregnancy, the mean IGF-BP/PP12 at 7–11 weeks was 43.3 μg/l, and at 36–40 weeks 121 μg/l. After early pregnancy termination the serum IGF-BP/PP12 decreased rapidly reaching a mean level of 8 pg/l within 4 days.

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