Estradiol (E2) is a form of estrogen, a key hormone involved in the regulation of the female reproductive system. The Estradiol test measures the level of this hormone in the blood and is commonly used to assess ovarian function, monitor fertility treatments, and evaluate menstrual irregularities. It is also used to check for conditions such as polycystic ovary syndrome (PCOS), menopause, or certain types of hormone-related cancers. Estradiol levels fluctuate throughout the menstrual cycle, so the timing of the test is important for accurate interpretation. In men, abnormal levels may indicate hormonal imbalances or underlying health issues.