What Is Serum FSH?

Follicle stimulating hormone (FSH) is a hormone made by the pituitary gland that plays a critical role in reproduction. The levels of this hormone vary throughout a person's life. Checking the serum FSH level can yield important information about the function of the ovaries, testes, pituitary gland, and hypothalamus. High levels could suggest menopause, ovarian failure, or testicular failure. Low levels might imply pregnancy or problems with the hypothalamus or pituitary glands.

The hormone FSH is made by the anterior pituitary gland, an endocrine gland located in the brain. It is a secreted in response to elevated levels of gonadotropin-releasing hormone (GnRH), manufactured by the hypothalamic region of the brain. Levels of FSH are regulated by a negative-feedback loop. In other words, having high serum levels normally shuts down further production of this hormone.

Follicle stimulating hormone is classified as a gonadotroph, which means that it helps to promote the growth and development of the gonads, a general term used to refer to the ovaries or the testes. In men, FSH promotes the growth of the testes, and helps produce a variety of molecules important for the proper growth and development of the sperm. The hormone has a different function in women, as it helps regulate the menstrual cycle and promotes the development of mature eggs.

The level of serum FSH, or the concentration of FSH in the blood, varies throughout a person's life. Typically levels are low or undetectable in puberty, and then rise after the onset of reproductive maturity. In women, the level fluctuates throughout the menstrual cycle, being high during the first half of the cycle and lower in the second half. After menopause, levels are typically elevated.

Checking the serum FSH is done for a number of reasons, and this hormone tends to be evaluated along with other reproductive hormones, including luteinizing hormone (LH), testosterone, and estrogen. Due to its important role in fertility and reproduction, its levels are often checked in the workup of an infertile couple. Sometimes the serum FSH level is checked in patients with early or late puberty. Additionally, knowing the amount of FSH in the blood could be useful in diagnosing whether a woman has reached menopause. It can also yield important information about women who have ceased having menstrual cycles, a condition known as amenorrhea.

High serum FSH levels can signify a number of different conditions. It might suggest the presence of either ovarian or testicular failure. Women who are post-menopausal typically have high levels of this hormone. A number of different illicit drugs can also cause high serum FSH.

Low serum FSH levels can also suggest a variety of diseases. Patients who have problems with either their hypothalamus or pituitary glands typically have low levels. Women who are pregnant also usually have low amounts of FSH in their bloodstreams. A number of medications, including corticosteroids and oral contraceptives, can suppress production of this hormone.