What It Is
Follicle stimulating hormone (FSH) is produced by the pituitary gland, a pea-sized gland in the brain that plays an important role in sexual development. An FSH test measures the level of this hormone in the bloodstream.
In kids, FSH levels are normally low. As puberty approaches (usually between ages 10 and 14), the brain produces gonadotropin-releasing hormone (GnRH), which starts the changes toward sexual maturity. GnRH signals the pituitary gland to release two puberty hormones into the bloodstream: FSH and luteinizing hormone (LH). Doctors often order a test for LH when ordering a blood test for FSH.
In boys, FSH and LH work together to get the testes to begin producing testosterone, the hormone responsible for the physical changes of puberty and the production of sperm.
In girls, FSH and LH prompt the ovaries to begin producing the hormone estrogen, which causes a girl's body to mature and prepares her for menstruation.
Because FSH and LH work so closely with each other, doctors often order these tests together, as well tests for testosterone (the male sex hormone) and estradiol (a form of estrogen, the female sex hormone). Taken together, the results can often provide a more complete picture of a child's sexual maturation.
Why It's Done
Doctors may order an FSH test if a boy or girl appears to be entering puberty earlier or later than expected. High levels are associated with precocious (early) puberty, while low levels may indicate a delay in sexual development.
The test may also be used to check for damage or disease of the testes or ovaries, pituitary gland, or hypothalamus, an almond-sized area of the brain that links the nervous system with the hormone-producing endocrine system.
In adults, FSH levels can also help doctors evaluate fertility issues and menstrual problems.
Preparation
No special preparations are needed for this test. On the day of the test, having your child wear a T-shirt or short-sleeved shirt can make things easier for the technician drawing the blood.