DUAL-LABEL TIME-RESOLVED IMMUNOFLUOROMETRIC ASSAY FOR SIMULTANEOUS DETERMINATION OF PREGNANCY-ASSOCIATED PLASMA-PROTEIN-A AND FREE BETA-SUBUNIT OF HUMAN CHORIONIC-GONADOTROPIN

Using time-resolved fluorometry, a simple one-step dual-label immunome tric assay has been developed, which allows simultaneous determination of pregnancy-associated plasma protein A (PAPP-A) and free beta-subun it of human chorionic gonadotrophin (beta-hCG) in first-trimester mate rnal serum samples. Two monoclonal antibodies were biotinylated and im mobilized onto the surface of streptavidin-coated microtitration plate s, and used to capture PAPP-A and beta-hCG, respectively. Europium (Eu ) and Samarium (Sm) chelates were conjugated to two additional monoclo nal antibodies acting as detection antibodies for PAPP-A and beta-hCG. The assay was performed using a 4-h one-step format. The within-run p recision with buffer-based calibrators was below 8% over the working r ange of PAPP-A (40-10 000 mIU/l) and beta-hCG (7.3-525 mu g/l) and no hook effect was observed. The intra-and inter-assay coefficients of va riation were below 7.1% for serum samples. PAPP-A and beta-hCG concent rations measured by the dual assay in 39 first-trimester serum samples correlated excellently with those obtained by DELFIA single-label PAP P-A (r=0.997) and the beta-hCG part (r=0.993) of the DELFIA AFP/beta h CG dual-label assay. (C) 1997 Elsevier Science B.V.