Estrogens are the hormones responsible for female sexual features such as breast development and the menstrual cycle. An estrogen test measures the level of the most important estrogens (estradiol, estriol, and estrone), usually through a blood sample.
In women, estrogens are produced mainly in the ovaries (and the placenta during pregnancy). Small amounts are also produced by the adrenal glands. In men, small amounts of estrogens are produced by the adrenal glands and testicles. Small amounts of estrone are made throughout the body in most tissues, especially fat and muscle. This is the major source of estrogen in women who have gone through menopause.
Estradiol is the estrogen that is most commonly measured in women who are not pregnant. The amount of estradiol in a woman's blood varies throughout her menstrual cycle. After menopause, estradiol production drops to a very low but constant level.
Estriol levels are usually measured during pregnancy to determine the likelihood of the fetus having Down's syndrome or other birth defects. Estriol can be detected as early as the 9th week of pregnancy, and its levels increase until delivery. This measurement is often included in a maternal serum "triple" or "quadruple" screening test.
Usually performed at between 16 and 18 weeks, these tests measure the amounts of three or four substances in a pregnant woman's blood. The triple screen measures alpha-fetoprotein (AFP), beta human chorionic gonadotropin (beta-HCG), and unconjugated estriol (uE3). The quad screen measures these substances as well as the hormone inhibin-A. The levels of these substances, along with a woman's age and other factors, help estimate the risk that her child may have certain problems or birth defects.
Estrone may be measured in women who have gone through menopause to determine their estrogen levels. It may also be measured in men or women (through a urine sample) as part of a total estrogen value when a tumor of the ovaries, testicles, or adrenal glands may be present.
A test for estrogen in the blood is carried out for reasons such as:
Women who are menstruating should note where they are in their menstrual cycle and give that information to the health professional collecting the blood sample.
When it comes to interpreting the results, normal values may vary widely from lab to lab and depend to a large extent on gender, age, menopausal status and pregnancy. Other factors include women undergoing Hormone Replacement Therapy (HRT); hormonal birth control such as pills or patches; having had a test involving radioactive substances within the previous week; the medication clomiphene (Serophene, Clomid); corticosteroids, such as dexamethasone (Decadron); high levels of sugar in the urine caused by diabetes.
Hormone levels fluctuate at different stages of pregnancy, making it difficult to isolate any underlying imbalances during this time.