An estradiol test is a blood test that measures the level of estradiol in the blood. The test is also known as an E2 test. Estradiol is a form of hormone estrogen which is also known as 17 beta-estradiol. Estradiol is made by the ovaries, adrenal glands, and breasts. Estradiol is also formed by the placenta during pregnancy. Estradiol helps in the growth and development of female sex organs which includes breasts, vagina, fallopian tubes, and uterus. Estradiol also helps in controlling the way the fat is distributed in the female body and is also an essential element for joint and bone health in females. Estradiol is also found in male bodies. In males, estradiol is made by the testes and adrenal glands but the levels of estradiol are lower than found in females.