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Estradiol. a subtype of estrogen (female sex hormone) is secreted by the ovaries. Biologically, of all the forms of estradiol, 1,7-estradiol is the most active. It is 12 and 80 times more potent than estrone and estriol respectively, which are the other forms of estrogen. Because of potency, estradiol is considered as a major estrogen for all the important functions related to female reproduction.

Estrogen is primarily synthesized in the ovaries and partially from adrenal androgens in adipose and other tissues. However, during pregnancy, primary production of estrogen occurs in the placenta. Estrogen is transported in the blood occurs bound to plasma proteins. For estradiol, 98% is transported by binding to sex hormone binding globin (SHBG).

Determining the estradiol levels helps in diagnosis, management and determining the prognosis of disorders in parts of the body responsible for secretion of estrogen-like estrogen-producing testicular and ovarian tumors, hyperplasia of the adrenal cortex, etc.

The level of estradiol is high during the stage in assisted reproduction where ovulation is induced and low during the early follicular phase. Enumeration of levels of estradiol is useful in monitoring ovulation induction as well as other conditions like amenorrhea, precocious puberty. In the male, these levels help in the diagnosis of hypogonadism. Decreased levels of estradiol indicate either lesion in the hypothalamus-pituitary axis or lack of ovarian synthesis.