Follicle-stimulating hormone and the FSH test explained

Follicle-stimulating hormone — also known as FSH — is a hormone produced in a small gland in the brain called the pituitary. Both males and females produce this hormone.

FSH is an important part of the reproductive system.

This article will explore the role of FSH, what FSH tests are for, what’s involved in an FSH test, and what different FSH levels mean. 

What does FSH do?

FSH plays a key role in sexual development and the reproductive system. 

While FSH is important for everybody, it takes its name from its ability to stimulate follicle growth in the ovaries. 

Follicles are responsible for producing certain sex hormones, including estrogen.

In females, FSH regulates the menstrual cycle and stimulates egg production in the ovaries. Levels of FSH fluctuate throughout the menstrual cycle and peak around the time an egg is released (ovulation).

In males, FSH regulates sperm production — along with testosterone — and remains at a constant level after puberty.  

Why do I need an FSH test?

Your doctor may request an FSH test for several reasons. 

For children, a doctor may request an FSH test if they transition into puberty earlier or later than expected. 

In adult females, an FSH test can help a doctor:

• identify reasons for difficulties getting pregnant

• check for pituitary gland disorders

• see how well the ovaries are working

• find out why periods have stopped or become irregular

The National Institute for Health and Care Excellence (NICE) in the United Kingdom also recommend considering an FSH test to diagnose menopause. 

In adult males, an FSH test can help a doctor:

• identify reasons for infertility

• see whether there is a pituitary gland disorder  

• determine how well the testicles are working

What happens during an FSH test?

An FSH test is a simple blood test that measures the level of FSH in your bloodstream. 

Generally, doctors will measure other hormones at the same time, such as estrogen in females and testosterone in males. 

You can also measure FSH in a urine sample. Urinary FSH home-testing kits are available in some pharmacies. 

You may choose to use home-testing kits if you're experiencing symptoms such as hot flashes, vaginal dryness, or irregular periods. 

FSH levels fluctuate throughout the menstrual cycle as well as during the menopause transition. There are also other reasons for high FSH levels, so this may not always mean menopause. 

FSH results may also vary depending on other factors, including:

• how much water you drank before testing

• the time of day you took the test

• other medications you’re taking, such as contraceptives or hormone replacement therapy (HRT)

What should my FSH levels be?

FSH levels differ depending on age and sex. FSH levels can also vary depending on where you are in your menstrual cycle. 

Also, results from different laboratories may differ slightly.

Typical ranges for males:

• before puberty: 0–5 international units per liter (IU/L)

• during puberty: 0.3–10 IU/L

• adults: 1.5–12.4 IU/L

Typical ranges for females:

• before puberty: 0–4 IU/L

• during puberty: 0.3–10 IU/L

• adults (still menstruating): 4.5–21.5 IU/L

• adults (after menopause): 25.8–134.8 IU/L

What do low levels of FSH mean?

In children, low levels of FSH may mean:

• ovary disorders in females

• testes disorders in males

In adult females, low levels of FSH may mean:

• a pituitary gland disorder

• a hypothalamus disorder

• problems producing eggs

In adult males, low levels of FSH may mean:

• a pituitary gland disorder

• a hypothalamus disorder

• problems with producing sperm

What do high levels of FSH mean?

In children, high levels of FSH may mean:

• Turner syndrome in females 

• Klinefelter syndrome in males

• an infection

• the onset of puberty

In adult males, high levels of FSH may mean:

• testicular disorders due to infection, chemotherapy, or radiotherapy

In adult females, high levels of FSH may mean:

• polycystic ovary syndrome (PCOS)

• an ovarian tumor 

• the onset of menopause 

FSH starts to increase around the time of menopause. This happens because as the ovaries decline and there are fewer follicles, they produce less estrogen. Because of the drop in estrogen, the brain signals the body to produce more FSH.

Summary

Both males and females produce FSH. It is an important reproductive hormone. If you need an FSH test, it generally involves a simple blood test. Urine tests are also available, but their results are less reliable. 

FSH levels will differ depending on age and sex. They can also vary depending on where you are in your menstrual cycle. 

For everyone, FSH outside the healthy range can be a sign of a pituitary gland disorder and can indicate problems with the reproductive system.