Estradiol is a female sex hormone, estrogen. It is usually synthesized by the ovaries, in small amounts by the testes in men, and by the placenta during pregnancy. In the blood, estradiol is transported by proteins: TeBG, SHBG and albumin. It is estimated that only 1-3% of estradiol is free – not bound to proteins. This hormone has many functions in the body, in particular in the regulation of the menstrual cycle, in the maintenance of secondary sexual characteristics – development of the breasts and genitals in women, but also on bone metabolism. Why is estradiol levels tested? Many conditions may require hormone testing. On the other hand, estradiol levels vary greatly during the menstrual cycle, so it is important to know at which point in the cycle the test is performed. The levels of FSH and LH – two other hormones involved in the regulation of the menstrual cycle – are measured at the same time. In women of childbearing age or those undergoing assisted reproduction procedures, it is important to monitor estradiol levels to monitor ovarian function and ovulation. Estradiol levels do reflect the stage of maturation and growth of ovarian follicles. The analysis of estradiol levels is also used in cases of sexual development disorders – lack of menstruation, premature puberty and others, to evaluate infertility or during menopause. In adult women, the examination of estradiol levels is also appropriate in case of suspicion of insufficient ovarian reserve or a hormonal problem of the pituitary gland – deficiency of FSH or LH. During menopause, the secretion of estradiol from the ovaries drops dramatically. The test can be performed before a decision is made to apply hormone replacement therapy. In men, estrogen tests are indicated in cases of abnormal breast development – gynecomastia and to diagnose hyperestrogenia – excessively high levels of female hormones. What results can be expected from an estradiol test? The analysis is performed through a blood sample. It is important to know the moment of the menstrual cycle when the test is performed. To assess the quality of the follicles in the ovaries, the test should be performed on the 3rd or 4th day of the menstrual cycle, along with a test of FSH levels. Estradiol concentrations are lowest during menstruation, then increase during the follicular phase until they peak just before the rise in LH levels, the luteinizing hormone that will trigger ovulation. Concentrations fall during ovulation and then rise again during the luteal phase. Regardless of cycle phase, blood levels are higher in the morning than in the afternoon. References: https://www.passeportsante.net/fr/Maux/analyses-medicales/Fiche.aspx?doc=analyse-oestradiol-sang