Estradiol is the primary form of estrogen in women and plays a crucial role in reproductive health, bone density, and cardiovascular health. This test measures estradiol levels in the blood to evaluate ovarian function and overall hormonal balance. Estradiol levels vary throughout the menstrual cycle, with peaks during ovulation and the luteal phase. This test is essential for evaluating menstrual irregularities, infertility, menopausal status, and various reproductive disorders. Low estradiol levels can indicate ovarian failure, menopause, or certain endocrine disorders, while high levels may suggest estrogen-producing tumors or hormonal imbalances. Estradiol testing is commonly ordered when evaluating amenorrhea, monitoring fertility treatments, assessing menopausal symptoms, or when investigating causes of feminization in men or precocious puberty in children. Understanding estradiol levels is crucial for proper reproductive health management and hormone replacement therapy decisions.