What Is a Growth Hormone Stimulation Test?
Growth hormone (GH) helps your bones and muscles grow and
develop properly. This hormone is produced by the pituitary gland, which is
located at the base of the brain.
GH levels naturally rise and fall over time. In some
individuals, however, hormone levels are higher or lower than they should be.
This can lead to a number of health problems, including decreased muscle mass,
delayed puberty, and low blood sugar levels.
There are tests and treatments that address excesses and
deficiencies of GH. One of these is the growth hormone stimulation test.
Why Is a Growth Hormone Stimulation Test
If a doctor suspects that your body is not producing enough
GH, they may order a GH stimulation test. A persistent shortage of GH is known
as growth hormone deficiency, or GHD. GHD is rare in all age groups, especially
adults, and testing is usually only done
when there is strong evidence that a person has this condition.
Symptoms of growth hormone deficiency in children include:
- below average height
- slower-than-normal growth
- poor muscle development
- low glucose levels in the blood
- delayed onset of puberty
Symptoms of GHD in adults are somewhat different, since adults
have already stopped growing. Symptoms include:
- reduced bone density
- decreased muscle strength
- increase in fat, especially around the waist
- problems sleeping
Your doctor may prescribe thyroid
tests before the growth hormone stimulation test, to rule out the thyroid as a
cause of your symptoms.
Hormone Stimulation Test Procedure
The following description should give you a general idea of
what to expect if your doctor orders a growth hormone stimulation test for you
or a member of your family. The procedure may vary slightly, depending on your
Before the Test
Your doctor will tell you if you need to stop taking certain
medicines before the test. Some medications known to affect GH levels include:
You will need to fast for 10 to 12 hours before the test.
During the Test
An IV will be placed in a vein in your arm or hand. The
procedure will feel very similar to having a blood sample taken. The major
difference is that after the needle is inserted, a tiny tube called an IV is
left inside the vein. There may be some discomfort when the needle pierces the
skin and some bruising afterward, but the risks and side effects are minimal.
An initial blood sample will be taken through the IV. This
and all subsequent samples will most likely be collected using the same IV
You will be given a growth hormone stimulant by IV. This is
a substance known to encourage an increase in GH production. The most commonly
used stimulants are insulin and arginine.
Several more blood samples will be taken at regular
intervals, usually over a period of a few hours. The entire procedure usually
takes about three hours.
After the Test
Your blood samples will be analyzed at a laboratory to see
whether your pituitary gland produced the expected amount of GH in response to
Results for a Growth Hormone Stimulation
The results for a growth hormone stimulation test show the
concentration of growth hormone in the blood sample. This concentration is
expressed in terms of nanograms of GH per milliliter of blood. This is how the
results are usually interpreted:
10 Nanograms of GH Per Milliliter of Blood, or Higher
Your growth hormone levels are within normal range. You do
not have growth hormone deficiency.
Between 5 and 10 Nanograms of GH Per Milliliter of Blood
In most cases, growth hormone deficiency cannot be
definitively diagnosed or ruled out. This range can be considered inconclusive.
However, in some cases, any measurement above 7 is
considered normal. This will depend on the lab.
5 Nanograms of GH Per Milliliter of Blood
Growth hormone levels are lower than normal. You will most
likely be diagnosed with GHD.
Doctors usually treat GHD by prescribing synthetic growth
hormone. This will supplement the growth hormone levels that naturally occur in
your body. The hormone is administered by injection. You will need to regularly
meet with your doctor. They will monitor your progress and adjust the dosage as
Children will often experience fast, dramatic growth during
treatment. In adults, treatment can lead to stronger bones, more muscle, less
fat, and other benefits.
There is some risk of side effects when on synthetic growth
hormone, such as headaches and muscle and joint pain. Serious complications are
rare. The dangers associated with treating GHD are usually surpassed by the