The growth hormone (GH) stimulation test measures the plasma level of human growth hormone (hGH) after the administration of the amino acid arginine and/or GH-releasing hormone. It measures the ability of the pituitary to secrete GH.
How the test is performed
An angiocatheter (IV) is usually placed in a vein, typically in the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band or blood pressure cuff is placed around the upper arm to cause the veins below the band to swell with blood.
A needle is inserted into the vein, and then removed while the angiocatheter is left in the vein. The band is then removed to restore circulation.
Your blood will be drawn 5 times. To prevent multiple punctures of the vein, samples will be taken through the IV line instead of repeatedly re-inserting the needle.
The first sample will be drawn between 6 a.m. and 8 a.m., then an intravenous (IV) infusion of arginine is started and continued for 30 minutes. After the 30-minute infusion, GH-releasing hormone is administered intravenously and then four more blood samples are drawn at 30-minute intervals.
(Sometimes arginine or GH-releasing hormone is given alone for this test. The variation of the test used depends on the preferences of the prescribing physician.)
How to prepare for the test
You will be asked to fast and limit physical activity for 10 to 12 hours before the test, or test results may be altered and invalidated.
If you are taking medications, your health care provider may ask that you withhold these before the test, as some can affect results. (Do not discontinue any medications without checking with your health care provider.)
You will be asked to relax for at least 90 minutes before the test, as exercise or increased activity can alter hGH levels.
If your child is to have this test performed, it may be helpful to explain how the test will feel. You may want to practice or demonstrate on a doll. This test requires temporary placement of an IV, and you should explain this to your child. The more familiar your child is with what will happen and the purpose for the procedure, the less anxiety he or she will feel.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise may develop at the site where the needle was inserted. These symptoms are temporary.
Why the test is performed
This test is typically performed to identify hGH deficiency as a cause of growth retardation.
A normal peak value is at least 10 ng/mL; 5-10 ng/mL is indeterminate; 5 ng/mL is subnormal. (A normal value rules out hGH deficiency; in some laboratories, the normal level is 7 ng/mL.)
Note: ng/mL = nanogram per milliliter.
What abnormal results mean
Failure of this test to raise hGH levels indicates there is a diminished amount of hGH stored in the anterior pituitary. In children, this results in dwarfism. In adults, it may be associated with panhypopituitarism or adult growth hormone deficiency.
What the risks are
Risks associated with drawing blood are slight:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
by Dave R. Roger, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.