Growth Hormone Suppression Test
Your pituitary gland is a small structure located at the base of your brain. It secretes several important hormones. One of these is growth hormone (GH). This hormone supports optimal growth and development in prepubescent children and proper bone density, muscle tone, and fat metabolism in adults.
If your levels of GH are too high or too low, it can lead to high cholesterol, chronic fatigue, or an enlarged heart.
Your doctor may order a GH stimulation test if they suspect that your GH levels are lower than they should be. Your doctor will order a GH suppression test if they suspect that your pituitary gland is producing too much GH. However, both of these conditions are very rare.
Conditions Associated with Excess Growth Hormone
Excess GH is associated with gigantism in children and acromegaly in adults.
Gigantism in children causes the long bones of your body to continue growing even when you’ve reached the end of puberty. People who have this condition can grow to be 7 feet or taller if their GH levels aren’t brought under control.
Acromegaly is a hormonal disorder in which your pituitary gland produces too much GH in adulthood. Acromegaly is characterized by:
- large hands and feet
- a protruding forehead and jaw
- widely spaced teeth
- thick lips
The condition can produce a variety of symptoms, including:
- numbness in your extremities
- elevated blood sugar and blood pressure levels
- heart problems, including an enlarged heart
Both of these conditions are extremely rare. The Hormone Health Network reports that about three new cases of acromegaly are diagnosed for every 1 million people each year. Only about 100 cases of gigantism have been reported in children in the United States, according to the Barrow Neurological Institute at St. Joseph’s Hospital and Medical Center.
How Do I Prepare for a Growth Hormone Suppression Test?
Although a GH suppression test involves only minimal pain, it takes longer to complete than standard blood work. Before the test, you may be asked to fast for 10 to 12 hours. However, drinking water is usually acceptable to have. You may be asked to limit your physical activity during the 10 to 12 hours before your test, and you should inform your doctor about any medications you’re taking.
What to Expect During the Test
When you arrive for your test, an IV line will be placed in a vein in your arm or hand. This will allow several blood samples to be taken from that vein. Unless you have a bleeding disorder, you’ll probably just feel a little pinch during this part of the procedure. Later, you may develop some slight bruising at the IV site.
You may be asked to lie still for a brief period. An initial blood sample will be taken from the IV line. You’ll then drink a glucose solution. This can make some people feel nauseous. If you experience nausea, try drinking it slowly or sucking on ice chips.
Several blood samples will be taken at regular intervals. For example, they may be taken every 30 minutes for two hours.
Your samples will be analyzed. If your GH levels are normal, consuming glucose will inhibit the production of more GH. If this doesn’t occur, then it’s a strong indication of excess GH production.
Treatments for Excess Growth Hormone
If you have higher-than-normal levels of GH in your blood, the cause is likely a tumor on your pituitary gland. The type of tumor that most likely causes excessive production of GH is an adenoma, which is noncancerous.
Your doctor can use surgery, radiation therapy, or medications to address excess GH production. These treatments may be combined in some cases.
Your doctor may be able to remove the tumor on your pituitary gland.
Radiation therapy may be used if surgery isn’t possible, if your entire pituitary gland is enlarged, or if the tumor has spread. This approach can lead to slow declines in your GH levels. It can sometimes take two to 10 years to see clinical improvement and permanent lowering of your GH secretions.
Radiation has serious side effects, including a decrease of normal production of other hormones from your pituitary gland. This leads to hypopituitarism. Hypopituitarism can affect your ovaries, testes, and adrenal and thyroid glands, resulting in deficient hormone secretion and non-functioning glands.
Medication should be considered a treatment for controlling rather than curing elevated GH levels. Your GH levels will spike when you stop taking the medication.
The medications most commonly used to lower growth hormone levels are growth hormone receptor antagonists, somatostatin analogs, and dopamine agonists.
The conditions associated with excess GH can have serious and sometimes lifelong consequences. Identifying conditions using the GH suppression test and other tools is an important first step in getting the ongoing and specialized care you need.
Your long-term outlook will depend on the underlying cause of your excess GH. Talk to your doctor to learn more about your condition and outlook.
How long does it usually take for results to become available after a GH suppression test?
Not every laboratory determines GH levels. Once the blood has been drawn, it may have to be transported to a laboratory that does this test. Doing the test in the laboratory takes less than a day. Once the test is done, it is then reported back to the laboratory that was initially involved, and then it’s reported to your physician. It should be available for you within a few days.William A. Morrison MDAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.