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
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.
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
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
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