What is an FSH Blood Test?

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An FSH blood test is used to investigate various medical conditions, including infertility, in both men and women and to see if a woman has entered menopause. It’s also a useful test to help determine why women are not having normal periods and for children who enter puberty too early or too late.

The FSH Blood Test in Women

An FSH blood test is one piece of information a doctor uses to explore why a woman isn’t having her period or why she’s infertile. If FSH blood levels are high, it usually indicates that a woman’s ovaries are not functioning normally. This may be because a woman is entering menopause or because she has a medical problem such as an autoimmune disease that’s causing her ovaries not to function normally.

Women who undergo cancer treatments may have a high FSH level due to premature ovarian failure as can women who have some genetic conditions or chromosomal abnormalities. FSH is usually measured along with LH, another hormone produced by the pituitary gland. If both are high, it further confirms the ovaries have failed.

When a woman has a low FSH level it can indicate a problem with the pituitary or a portion of the brain called the hypothalamus. The pituitary gland normally produces FSH under the direction of the hypothalamus. The FSH that’s produced sends a message to the ovary to produce more of the female hormone estrogen. If the pituitary gland is damaged due to a stroke or a tumor, it may not produce enough FSH.

FSH levels can also be low with certain genetic conditions and with a common condition called polycystic ovary disease. Women who suffer from poor nutrition or who are under extreme stress may also have low FSH levels.

The FSH Blood Test in Men and Children

An FSH level may be ordered in a man to find out why a couple is having fertility problems. Similar to women, a high FSH level in men is often due to testicular failure which can come from cancer treatment, autoimmune disease, tumors, trauma to the testicles or even viral infections. Various chromosomal abnormalities can also cause high FSH levels in men.

Low FSH levels in men as in women indicate the problem lies with the pituitary or hypothalamus, not the testicles, and will probably require brain imaging to rule out a tumor or other problem.

An FSH blood test is also used to find out why a child has undergone puberty at a very early age or why puberty is delayed.

An FSH Blood Test is Simple to Perform

Getting an FSH blood test is as simple as drawing a tube of blood, but your doctor may recommend stopping certain medications that can alter the results for several weeks before the test. It’s important that women know the date of the last menstrual period to better interpret the results, and, in some cases, more than one FSH level may be drawn, especially if a man or woman is having fertility problems.

The Bottom Line?

An FSH blood test is an important test for diagnosing fertility problems in both men and women and for determining why a child isn’t entering puberty at the proper time. It also helps to identify when a woman has entered menopause. Ask your doctor if this test is right for you.


Lab Tests Online. “FSH”

Web MD. “Follicle-Stimulating Hormone”

Merck Manual. Eighteenth edition. 2006.

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