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.
Reasons for Testing
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.
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 testing location.
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 line.
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 the stimulant.
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 needed.
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 potential benefits.