Oestradiol (E2) is the most potent and biologically active form of oestrogen and the primary oestrogen produced by the ovaries during the reproductive years. It plays a fundamental role in female reproductive health — regulating the menstrual cycle, supporting uterine lining development, and maintaining bone density, skin integrity, cardiovascular health, and cognitive function.

In men, oestradiol is produced in smaller amounts through the conversion of testosterone by the enzyme aromatase. While necessary for bone health and libido in men, elevated oestradiol in males can cause gynaecomastia (breast tissue growth) and fertility problems. Oestradiol testing is used across a wide range of clinical situations including cycle monitoring, fertility treatment, investigating menopausal symptoms, and hormonal therapy.