A growth hormone (GH) test measures the amount of human growth hormone (GH) in the blood. GH is made by the pituitary gland and is needed for growth. It plays an important role in how the body uses food for energy (metabolism). The amount of GH in the blood changes during the day and is affected by exercise, sleep, emotional stress, and diet.

Too much GH during childhood can cause a child to grow larger than normal (gigantism). Too little GH during childhood can cause a child to grow less than normal (dwarfism). Both conditions can be treated if found early.

In adults, too much GH is caused by a noncancerous tumor of the pituitary gland (adenoma). Too much GH can cause bones of the face, jaw, hands, and feet to grow larger than normal (acromegaly).

Growth hormone can cause the release of other substances (factors) that affect growth and metabolism. One of these is insulin-like growth factor 1 (IGF-1). When the GH level is very high, the IGF-1 level is also very high. A test for IGF-1 may also be done to confirm high GH levels.

Why It Is Done

A test for growth hormone (GH) is done to:

• See whether a child whose growth is abnormal has dwarfism or gigantism.
• See whether an adult has acromegaly. This condition is caused by a tumor (adenoma) of the pituitary gland.
• Check treatment that uses growth hormone.

How To Prepare

Do not exercise or eat or drink anything for 10 hours before the test. You may be asked to sit quietly for 30 minutes right before the test.

Certain medicines can affect growth hormone test results, such as corticosteroids and estrogens (including birth control pills). Your health professional may ask you to stop taking these medicines before the test.

How It Is Done

Blood levels of growth hormone (GH) can change quickly, so more than one blood sample may be taken on different days. Insulin-like growth factor 1 (IGF-1) levels change more slowly, and it may be the first test done.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.