Improved detection of serum estradiol after sample extraction procedure.

The direct measurement of serum estradiol offers advantages over the more traditional sample extraction and immunoassay methods with respect to technical ease of the assay and turnaround time. However, direct assays have not been demonstrated sufficiently sensitive for some important clinical applications, including the measurement of circulating estradiol in women during the early follicular phase of their menstrual cycle, in postmenopausal women, and in men. We report here a rapid sample extraction method developed to improve the detection limit of automated estradiol assays and thus enhance the potential usefulness of these rapid and nonisotopic systems for measuring low concentrations of serum estradiol. Serum estradiol concentrations have long been used in conjunction with ultrasonography and other clinical indices to monitor ovarian stimulation by exogenous gonadotropin therapy during in vitro fertilization (IVF) procedures (1)(2)(3). With the recent use of gonadotropin-releasing hormone agonists, serum estradiol measurement has also been used to assess the adequacy of ovarian suppression before exogenous gonadotropin stimulation. In addition, it has become increasingly important to measure the low initial concentrations of serum estradiol (<150 ng/L) associated with the earlier stages of ovarian follicular stimulation (4)(5). Clinically important measurements of low estradiol concentrations are also required in assessing ovarian activity in perimenopausal women or women experiencing premature ovarian failure and in clinical investigations of the hypothalamic-pituitary-gonadal axis in men (6)(7)(8). Methods for the direct measurement of serum estradiol are replacing the more traditional RIA methods that use preassay sample extraction followed by RIA with antecedent column chromatography. Direct methods are advantageous because they are rapid and less technically demanding. However, direct assays are often inaccurate, particularly for the measurement of relatively low concentrations of serum estradiol (9)(10)(11). The presence of sex-hormone-binding globulin in serum and …

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