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 taller 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
No special preparation usually is required before having this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
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 on the site and then put on a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
A growth hormone (GH) test measures the amount of human growth hormone (GH) in the blood.
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Less than 10 ng/mL (less than 452 pmol/L)
Less than 20 ng/mL (less than 904 pmol/L)
- High GH values may mean gigantism or acromegaly is present. These conditions are caused by a noncancerous tumor in the pituitary gland (adenoma). Insulin-like growth factor 1 (IGF-1) levels should also be high.
- High GH levels may also be caused by diabetes, kidney disease, or starvation. These conditions do not cause high IGF-1 levels.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Taking medicines, such as amphetamines, corticosteroids, insulin, or estrogens.
- Having low blood sugar (hypoglycemia).
- Being obese.
- Taking the herb St. John's wort.
What To Think About
- Normal levels of growth hormone (GH) change during the day so other tests may be done to confirm the results of a GH test. Other tests can show whether low levels of GH (which can be normal) mean the pituitary gland is not working correctly.
- IGF-1 blood levels are often done at the same time as a GH test. A high level of IGF-1 with a high level of GH generally means acromegaly is present. In this case, magnetic resonance imaging (MRI) is done to look at the pituitary gland. To learn more, see the topic Magnetic Resonance Imaging (MRI) of the Head.
- The growth hormone suppression test (also called the glucose loading test) measures the level of GH in the blood before and after a person drinks fluid with a large amount of sugar (glucose) in it. Normally, the amount of GH drops to less than 1 ng/mL after drinking the glucose. Levels of GH that stay high may mean acromegaly is present.
- The growth hormone stimulation test measures the level of GH in the blood before and after insulin or arginine is given in a vein (intravenously) in the arm. No detectable growth hormone can be found for people with normal pituitary function. A growth hormone stimulation test may be used to see if a person lacks GH. Normally, the amount of GH increases after insulin or arginine. A GH level that does not increase after the insulin or arginine is given may mean the person lacks growth hormone.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Primary Medical ReviewerKathleen Romito, MD - Family Medicine
Specialist Medical ReviewerAlan C. Dalkin, MD - Endocrinology
Current as ofNovember 20, 2015