Synthesis of a novel biotin-estradiol conjugate and its use for the development of a direct, broad range enzyme immunoassay for plasma estradiol

The synthesis and purification by high pressure liquid chromatography of a novel biotinoyl-diaminodioxaoctane-estradiol conjugate is described. The conjugate was used for the development of an enzyme Immunoassay (EIA) for the direct determination of estradiol in human plasma. This assay was characterized by a low limit of detection (77 pM) and a broad working range. Estradiol concentrations ranging from 77 to 24300 pM, i.e. from the lower levels observed in the follicular phase of the normal menstrual cycle to the very high levels attained during hyperstimulation for in vitro fertilization, could be determined directly in undiluted plasma samples. Intra-assay variation ranged from 3.6 to 10.9% and interassay variation from 6.1 to 12%. The results obtained by the present EIA correlate well with target values obtained by isotope-dilution gas chromatography-mass spectrometry (r = 0.96) and with results obtained by a direct RIA (r = 0.97). The EIA requires no special apparatus, is simple, fast and robust, and could be applied in any clinical laboratory.