Blood Test: Follicle Stimulating Hormone (FSH)

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.

The Procedure

A health professional will clean the skin surface with antiseptic, and place an elastic band (tourniquet) around the upper arm to apply pressure and cause the vein to swell with blood. Then a needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.

After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting the blood for this test will only take a few minutes.

What to Expect

Collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.

Getting the Results

The blood sample will be processed by a machine. The results usually are available after a day or two.

Risks

The FSH test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, like:

• fainting or feeling lightheaded
• hematoma (blood accumulating under the skin causing a lump or bruise)
• pain associated with multiple punctures to locate a vein

Helping Your Child

Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.

Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.

If You Have Questions

If you have questions about the FSH test, speak with your doctor.