Measurement of estradiol in serum or plasma is considered to be the most reliable way to assess its rate of production. Estradiol (17ß-estradiol) is a steroid hormone (molecular weight of 272.3 Daltons), which circulates predominantly protein-bound. In addition to estradiol, other natural steroidal estrogens include estrone, estriol and their metabolites. Natural oestrogens are hormones secreted principally by the ovarian follicles and also by the adrenals, corpus luteum and placenta.

The Biorex Diagnostics Estradiol kit is a colorimetric enzyme-linked immunosorbent assay (ELISA) intended for the quantitative determination of estradiol concentration in human serum or plasma.