Hormone Blood Tests for Women

Hormone blood tests can reveal an abundance of important information about a woman's health. Levels of estrogen can reveal where a woman is in her menstrual cycle, for example, which can help pinpoint the cause of fertility problems or signal the onset of menopause.

Blood tests to measure female hormone levels also can play a role in diagnosing medical conditions such as thyroid disease or diabetes, and they can help evaluate how well a medication is working.

The female hormones typically evaluated—often as part of a comprehensive hormone panel in which more than one hormone is tested—are estrogen, progesterone, follicle-stimulating hormone (FSH), testosterone/DHEA, and thyroid hormones. What the results of testing these hormones mean will depend on whether the levels are higher than normal or lower than normal.

Estrogen is not a single hormone, but rather a group of three hormones: estradiol (E2), estriol (E3), and estrone (E1). Of these, estradiol is the major sex hormone responsible for, among other things, sexual functioning, healthy bones, and female characteristics. 

In premenopausal women, estradiol is produced mainly by the ovaries. Estradiol levels vary throughout the menstrual cycle and are highest at ovulation and lowest at menstruation. They decrease slowly with age; the largest drop occurs at menopause when the ovaries "switch off."

Low estrogen levels may be a sign of polycystic ovarian syndrome (PCOS), decreased pituitary function (hypopituitarism), low testosterone (hypogonadism), anorexia nervosa, or low body fat. Certain medications, such as Clomid (clomiphene), also can cause a decline in estrogen levels.

High estrogen levels may occur with conditions such as obesity, diabetes, high blood pressure. Certain medications, including steroid hormones, phenothiazines, tetracycline antibiotics, and ampicillin, also are known to increase estrogen levels.

Progesterone is produced by the ovaries during ovulation. Its function is to help prepare the uterus to receive a fertilized egg.

When an egg is released from an ovary during ovulation, the remnants of the ovarian follicle (the corpus luteum) will release progesterone along with small amounts of estradiol. If the egg is not fertilized, the corpus luteum will break down, progesterone levels will plummet, and a new menstrual cycle will begin.

If the egg is fertilized, progesterone will stimulate the growth of blood vessels that supply the endometrium (the lining of the womb). At the same time, it will stimulate glands in the endometrium to secrete nutrients to nourish the developing embryo.

Low progesterone levels during pregnancy often foreshadow miscarriage and premature labor. Expectant women at risk of preterm birth may be given a synthetic form of progesterone to prevent the early onset of labor.

Progesterone levels may be measured to help pinpoint the cause of infertility or assess the risk of miscarriage.

Follicle-stimulating hormone (FSH) is produced by the pituitary gland. It stimulates the growth of an egg (follicle) in the ovary to get it ready for fertilization.

As estrogen and other hormone levels begin to decline—during menopause or diminished ovarian reserves (when the ovaries lose their reproductive potential)—the pituitary gland will produce more FSH to compensate for this loss.

The FSH test  may be used to evaluate conditions such as abnormal menstrual bleeding, infertility, menopause, PCOS, pituitary gland tumors, and ovarian cysts.

If FSH levels are too high, it's usually because the ovaries are malfunctioning; the problem rarely lies with the pituitary gland. On the other hand, low FSH levels are often caused by a disease or congenital defect of the hypothalamus, pituitary gland, or the hypothalamic-pituitary axis.

Although testosterone typically is regarded as the "male sex hormone," women also produce it. In fact, testosterone is the precursor of estradiol: Most of the testosterone a produced in a woman's ovaries and adrenal glands is converted to estradiol with the help of an enzyme called aromatase.

High testosterone levels may result in irregular or missed menstrual periods, weight gain, acne, and infertility, as well as what's known as virilization: the development of secondary male traits such as excess body hair, deepened voice, and male-pattern hair loss.

Low testosterone may occur during menopause and result in a significantly decreased sex drive (libido). 

Like testosterone, dehydroepiandrosterone (DHEA), is classified as an androgen. An elevated DHEA level may occur with conditions such as congenital adrenal hyperplasia or cancer of the adrenal gland.

Thyroid function is measured and characterized by a group of hormones produced by the pituitary gland or the thyroid gland itself. The three main ones are:

• Thyroid-stimulating hormone (TSH), a pituitary hormone that signals the thyroid gland to produce more or less hormone
• Thyroxine (T4), a "storage" hormone that needs to be converted to an active state
• Triiodothyronine (T3), the "active" thyroid hormone created from the conversion of thyroxine

Elevated thyroid hormones (hyperthyroidism) may cause weight loss, goiter, hyperactivity, and irregular and/or light menstrual periods.

By contrast, low thyroid hormone (hypothyroidism) during pregnancy can lead to preeclampsia, placental abruption, miscarriage, preterm birth, low birth weight, and congenital thyroid problems.