Growth Hormone with Stimulation (Blood)
Does this test have other names?
GH, GHD, arginine, insulin tolerance test or insulin-induced hypoglycemia, clonidine, L-dopa, glucagon, growth-hormone-releasing hormone, GHRH
What is this test?
This test measures the level of growth hormone (GH) in your blood.
GH is made in your pituitary gland. It affects height, bone, and muscle growth in children. It affects how adults look and feel, as well as their bone and muscle health.
GH is made in a pulse-like manner. Most GH is made while you sleep. When you're awake, little or possibly no GH is found in your blood. That makes it hard to test your GH level. Specialists have developed methods to figure out if you make too little GH by testing your blood over time after stimulating GH production. If your GH level does not rise to a certain range, you may have growth hormone deficiency.
These are different kinds of stimulation that may be used in this test:
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Insulin is the best way to stimulate GH. It's the most powerful GH stimulant and the most specific, but it isn't safe to use with everyone. Sometimes this test is called "insulin-induced hypoglycemia." If your doctor decides an insulin tolerance test is right for you or your child, blood samples are taken 30, 60, and 120 minutes after the insulin is given.
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Arginine is given into a vein over a period of 30 minutes. Blood samples are taken every half hour at 0, 30, 60, 90, and 120 minutes. Arginine can be given alone, or with a dose of growth-hormone-releasing hormone (GHRH).
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Glucagon is a good choice for infants and young children because it's given right under the skin. Blood is taken between one and three hours, with a peak in GH expected between two and three hours.
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Clonidine is the quickest test. Peak GH secretion happens about an hour after it's given.
Why do I need this test?
You might have this test if your doctor suspects that you have a growth hormone deficiency. Signs include:
Your child might need this test if he or she has these signs:
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Slow growth, or in the lower third percentile for height
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Short stature for his or her age, or less than 0.5 percentile for age height
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Delayed puberty
What other tests might I have along with this test?
Your doctor may also order a blood test for insulin-like growth factor-1 (IGF-1). GH tells your liver to make IGF-1, so usually GH and IGF-1 are correlated. GH is secreted in pulses while you sleep, but IGF is always found in your blood. That makes it much easier to find IGF-1 in your blood than GH.
Your child's doctor may also order a test for insulin-like growth factor binding protein-3, IGFBP-3. This protein is made by the liver and works with IGF-1.
Your doctor may also order an MRI to check for a pituitary gland tumor. Children may also have a bone age test.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Normal results differ by age. All growth hormone deficiency tests take age into account.
If your levels of GH are lower, it may mean that you have a pituitary tumor. It may also mean you have hypopituitarism, a condition in which the pituitary gland makes low amounts of many kinds of hormones, including GH.
Lower levels in children may be present from birth or they may be caused by head trauma, a tumor, or radiation therapy. If a low GH level is not caused by a damaged pituitary gland, sometimes the child outgrows it by adolescence or young adulthood. Your doctor may want to retest at different stages of your child's development.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
When testing for GH deficiency, the insulin tolerance test is not recommended for anyone with a history of seizures, heart issues, or problems with blood vessels in the brain.
What might affect my test results?
Sleeping, certain foods and beverages, exercising can all affect your results.
How do I get ready for this test?
You will need to avoid eating or drinking anything but water the night before and the morning of the test. In addition, be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.