Growth Hormone Suppression Test
The pituitary gland is a small structure located at the base of the brain. It secretes several important hormones. One of these is the growth hormone (GH). This hormone supports optimal growth and development in prepubescent children and proper bone density, muscle tone, and fat metabolism in adults.
Serious consequences, including high cholesterol, chronic fatigue, and an enlarged heart, can result if your levels of GH are too high or too low.
Your doctor may order a growth hormone stimulation test if he or she suspects that your GH levels are lower than they should be. The doctor will also order a growth hormone suppression testif he or she suspects that your pituitary gland is producing too much growth hormone. However, both of these conditions are very rare.
What to Expect
Although a growth hormone suppression test involves only minimal pain, it takes longer to complete than standard blood work. Prior to the test, you may be asked to:
- fast for 10 to 12 hours (drinking water is usually acceptable)
- limit physical activity during the 10 to 12 hours leading up to the test
- inform your doctor about any medications you are taking
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 will 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 will then drink a glucose solution. This can make some people feel nauseous. If you experience nausea, try drinking it a little slowly or sucking on ice chips.
Several blood samples will be taken at regular intervals (e.g., 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 growth hormone. If this doesn’t occur, then it is a strong indication of excess growth hormone production.
Conditions Associated with Excess Growth Hormone
Excess growth hormone is associated with gigantism in children and acromegaly in adults.
Gigantism in children causes the long bones of the body to continue growing even when the individual has reached the end of puberty. Individuals who have this condition can grow to be 7 feet or taller if GH levels aren’t brought under control.
Large hands and feet, a protruding forehead and jaw, widely spaced teeth, and thick lips characterize acromegaly. Acromegaly can produce a variety of symptoms, including:
- numbness in the extremities
- elevated blood sugar and blood pressure
- heart problems, including an enlarged heart
Both of these conditions are extremely rare. According to the Hormone Health Network, only 60 out of every 1 million American adults have acromegaly, and fewer than 100 children in the entire country have gigantism (HHN, 2012).
Treatments for Excess Growth Hormone
The likely cause of higher-than-normal levels of GH in your blood is a tumor on your pituitary gland. The type of tumor that causes excessive production of growth hormone is an adenoma. It is typically noncancerous.
Doctors use three main approaches to address excess growth hormone production: surgery, radiation therapy, and medications. These treatments may be combined in some cases.
If possible, the tumor on your pituitary gland will be removed.
Radiation therapy may be used if surgery isn’t possible and the entire pituitary gland is enlarged or tumor has spread. This approach can lead to slow declines in GH levels. It can take sometimes take two to 10 years to see clinical improvement and permanent lowering of GH secretion.
Radiation has serious side effects, including the decrease of normal production of other hormones from the pituitary gland. This leads to hypopituitarism. Hypopituitarism can affect ovaries, testes, and adrenal and thyroid glands, resulting in deficient hormone secretion and non-functioning glands.
Medication should be considered a control rather than a cure. GH levels will spike when an individual stops taking the medication. The three medications most commonly used to lower growth hormone levels are called growth hormone receptor antagonists, somatostatin analogues, and dopamine agonists.
The conditions associated with excessive GH can have serious and sometimes lifelong consequences. Identifying conditions using diagnostic tools such as the growth hormone suppression test is an important first step in getting patients the ongoing and specialized care they need.