What is Estradiol (17β-Estradiol), Serum?
17β-Estradiol is the most potent endogenous oestrogen and the primary oestrogenic steroid in premenopausal women. It is synthesised predominantly by granulosa cells of developing ovarian follicles through aromatisation of testosterone under FSH stimulation via the enzyme aromatase (CYP19A1) — a reaction requiring androstenedione or testosterone as substrate. During the menstrual cycle, estradiol rises progressively through the follicular phase as the dominant follicle develops, peaks sharply at the mid-cycle LH surge (the ovulatory peak) reaching 200–400 pg/mL or higher in stimulated cycles, falls briefly at ovulation, rises again during the luteal phase under corpus luteum support, then falls precipitously before menstruation. In postmenopausal women, ovarian follicular oestrogen production ceases, with residual circulating estradiol derived from peripheral aromatisation of adrenal androgens — predominantly androstenedione — in adipose tissue, liver, muscle, and skin. Estradiol exerts its biological effects through nuclear oestrogen receptors ERα and ERβ, and membrane-associated receptors including GPER1, regulating hundreds of gene targets across reproductive, skeletal, cardiovascular, neurological, and metabolic tissues. Its plasma half-life is approximately 1–2 hours.