An estradiol test measures the amount of a hormone called estradiol in the blood. Estradiol is the most important form of estrogen found in the body. Most of it is made in and released from the ovaries, adrenal cortex, and the placenta, which forms during pregnancy to feed a developing baby.

Estradiol is responsible for the growth of the female uterus, Fallopian tubes, and vagina. It promotes breast development and the growth of the outer genitals. The hormone plays a role in the distribution of body fat in women and stops the process of growing taller.

This test is used to check the function of the ovaries, placenta, or adrenal glands. This test may be ordered if certain types of ovarian tumors are suspected, when there is delayed or abnormal development of male or female body characteristics, or the menstrual cycle is absent. A woman's level of estradiol can vary widely, depending on where she is in her menstrual cycle.

Women undergoing assisted reproductive technology (ART) for infertility may have this test at regular intervals in combination with ultrasound imaging to monitor their ovaries' response to stimulation.