Definition
Growth hormone (GH) testing measures the level of human growth hormone in the blood. GH is a hormone made in the pituitary gland in the head. Your doctor may order one of the following tests if you have symptoms that suggest a GH abnormality:
- Suppression test—measures the amount of GH that is produced when the pituitary gland is told not to produce any GH
- Stimulation test—measures the function of the pituitary gland to secrete GH when it is told to secrete GH
There are many factors that can interfere with GH testing. Stress, exercise, certain medicines, and blood glucose levels can all cause GH levels to rise and fall. For this reason, GH tests are often done with other hormones, like IGF-1 (insulin-like growth factor-1).
Reasons for Test
Suppression tests are ordered:
- For children who show symptoms of gigantism
- For adults who show signs of acromegaly (abnormally large bone growth)
- To check for abnormalities in the function of the pituitary gland
- If a tumor in the pituitary gland is suspected—This is done with another test called IGF-1 (insulin-like growth factor 1) that does not vary so much over time.
- To monitor the effectiveness of GH replacement (commonly done with IGF-1 test)
GH stimulation tests are ordered:
- For children who are significantly short for their age
- When thyroid testing rules out a problem with the thyroid but growth is slower than expected
- To check for abnormalities in the function of the pituitary gland
- For children who have had radiation therapy
- For children whose bones are not developing normally
- For adults with symptoms of muscle weakness, lack of energy, thin skin, weak bones, and other symptoms that when taken together, suggest a lack of GH
- For adults with pituitary disorders that increase the risk of growth hormone deficiency
Possible Complications
There are no major complications associated with this procedure.
What to Expect
Prior to Test
To prepare for the procedure, most patients will need to:
- Fast for 10-12 hours before the test.
- Reduce physical activity for 10-12 hours before the test.
- If instructed by your doctor, stop taking regularly prescribed medicine before the test.
- Ninety minutes before the test, rest and relax. Avoid physical activity.
Description of Test
To Collect Blood
The injection site will be cleaned. An elastic tie will be placed around the upper arm. A needle will be inserted into the vein. The blood will be collected in a vial. Once the vials are full, the needle will be removed from the skin. Pressure will be put on the puncture site.
Suppression Testing
A blood sample will be taken between 6 am and 8 am. You will be asked to drink a water and glucose (sugar) solution. The glucose should make the GH level in the blood lower. Two more blood samples are taken within one to two hours after you have consumed the solution. In each blood sample, the GH level will be measured. IGF-1 levels may also be measured since they do not vary so much.
Stimulation Testing
Insulin Tolerance Test
Blood samples will be drawn five times at different intervals. A first sample for blood glucose, cortisol, and growth hormone will be taken between 6 am and 8 am. Then, insulin will be given through the IV. The insulin should make the blood glucose level go down, which should make the GH level go up. Blood samples will be collected at 30, 60, 90, and 120 minutes for glucose, cortisol, and growth hormone.
If the blood sugar has not dropped to a certain level after 45 minutes, a repeat dose of insulin will be given. The blood sample will be collected 75 minutes and 150 minutes later. If the blood sugar levels fall too low, a high dose of sugar will be given by IV, followed by a sugar infusion.
Growth Hormone-Releasing Hormone, Arginine, Growth Hormone-Releasing Peptide
The blood sample will be drawn five times at different intervals. The first sample will be taken between 6 am and 8 am. Arginine or GH-releasing peptide will be given through the IV for 30 minutes. Once the arginine or GH-releasing peptide has been administered, GH-releasing hormone will be given by IV. This should stimulate the pituitary to release GH. The last four blood samples will be drawn every 30 minutes following both infusions.
Note: GHRH is not currently available commercially in the United States.
After Test
You will be able to leave after the test is done.
How Long Will It Take?
The procedure often takes at least three hours.
Will It Hurt?
There may be some minor discomfort when the needle is inserted in the skin and during the infusions. A doctor will supervise the insulin tolerance, as insulin can cause a very low blood sugar level in the blood.
Results
Your doctor will discuss the results of the test. You may need further testing or treatment.
Call Your Doctor
After the test, call your doctor if any of the following occurs:
- Symptoms of infection, including fever and chills
- Severe redness, pain, or drainage from the puncture site
In case of an emergency, call for medical help right away.