An Estradiol Test, also known as E2 test, measures the levels of estradiol, a form of estrogen, in the blood. This hormone is primarily produced by the ovaries in women and plays a crucial role in regulating the menstrual cycle and maintaining reproductive health. In men, estradiol is produced in smaller amounts by the testes. The test is often ordered to assess fertility, monitor hormone replacement therapy, diagnose hormonal imbalances, or evaluate certain medical conditions. It can help determine the cause of irregular menstrual cycles, infertility, and symptoms like hot flashes and mood swings.