FSH test explained

FSH is a hormone made by the pituitary gland. In women it stimulates the maturation of follicles (the sacs that hold the eggs) in the ovaries; in men it drives sperm production in the testes. In a woman's body the amount of FSH changes across the menstrual cycle: it rises at the start of the cycle, when follicle growth is being stimulated, and changes again in the later phases. After menopause, when the ovaries no longer produce enough oestrogen, the pituitary releases more and more FSH in an attempt to stimulate them — which is why the FSH level rises sharply. In men FSH sustains continuous sperm production, and its amount is relatively more stable.

An FSH test is usually done together with LH (luteinising hormone), estradiol or testosterone, because these hormones act in relation to one another — through the pituitary-gonadal axis. The test helps to assess fertility, menstrual disturbances, the onset of menopause and testicular function.

• When a pregnancy does not happen after a year of unsuccessful attempts — as part of assessing fertility
• When periods are irregular or absent altogether
• When the onset of menopause, or its approach, is suspected
• In men — when infertility or a low sperm count is suspected
• In children — when puberty starts unusually early or is delayed
• When there is reduced sex drive, tiredness, weakness, or reduced muscle mass and body hair

A raised FSH most often means that the ovaries or the testes themselves are not producing enough sex hormones, so the pituitary compensates by producing more FSH. In women this is most often linked to menopause approaching or a reduced ovarian reserve; in men, to damage to the testes. It is assessed together with LH, estradiol or testosterone.

• Menopause or its approach (including premature menopause)
• Reduced ovarian function (primary ovarian insufficiency)
• Pituitary tumours
• Turner syndrome in women, Klinefelter syndrome in men
• Damage to the testes from alcohol, chemotherapy or radiotherapy
• Hormone therapy

What to discuss with a doctor

• An LH, estradiol or testosterone test — to assess the whole pituitary-gonadal axis
• The menstrual cycle history and menopause symptoms
• Family and treatment history (chemotherapy, radiotherapy)
• When to repeat the test if the result is borderline

A low FSH most often points to a disorder of the pituitary gland or the hypothalamus, because of which the ovaries or the testes are not stimulated enough. In women, severe weight loss or a heavy physical load can contribute to this, and so can pregnancy.

• A disorder of the pituitary gland or the hypothalamus
• Very low body weight or rapid weight loss
• Absence of ovulation
• Pregnancy

What is usually assessed after a low result

• An LH test and other pituitary hormones
• Assessment of diet, weight changes and physical load
• A check for possible pregnancy in women
• When to repeat the test to assess the change

Laboratory ranges and related pages

The interval used by a particular laboratory may differ slightly from the ones given here, so the exact interval is the one printed on your own report. A doctor assesses the result together with LH, estradiol or testosterone, the symptoms and, if the result is borderline, a repeat test. Related pages: LH, estradiol, prolactin, how to prepare for a blood test and how to read blood test results.