As its name suggests, growth hormone(GH) helps bones and muscles grow and develop properly. This hormoneis produced by the pituitary gland,which is located at the base ofthe 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.
Targeted tests and treatments address excesses and deficiencies of GH. One of these is the growth hormone stimulation test.
If a physician suspects that your body is not producing enough growth hormone, he or she may order a GH stimulation test. A persistent shortage of GH is known as growth hormone deficiencyor GHD. It 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 growth hormone deficiency in adults are somewhat different becausethey have already stopped growing. They include:
- reduced bone density
- decreased muscle strength
- increase in fat, especially around the waist
- sleep problems
The procedure below may vary slightly depending on yourtesting location. 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.
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.You may be asked to stop all physical activity for 90 minutes 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, probably over a period of a few 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 (ng/mL). The table below shows how the test results are usuallyinterpreted:
Peak Growth Hormone Concentration in Blood Sample(s) (ng/mL)
What It Means
10 ng/mL or higher
Growth hormone levels are within the normal range. The patient does not have growth hormone deficiency.
Between 5 ng/mL and 10 ng/mL
In most cases, growth hormone deficiency cannot be definitively diagnosed or ruled out. This range can be considered inconclusive.
*Note: In some cases, any measurement above 7 ng/mL is considered normal. This will depend on the lab.
5 ng/mL or lower
Growth hormone levels are lower than normal, indicating growth hormone deficiency.
Doctors usually treat GHD by prescribing synthetic growth hormone to supplement naturally occurring levels in the body. The hormone is administered by injection. The doctor will regularly 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.
While there is some risk of side effects 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.