Growth hormone suppression test

How the Test is Performed:
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .

A total of three blood specimens are taken. The first is collected between 6 and 8 a.m. Then you are asked to drink a water solution with 75 grams of glucose. Drink this slowly or you may become nauseated; however, the solution must be consumed within 5 minutes or the test results may be altered.

The blood samples are collected 1 to 2 hours after you finish drinking the glucose solution. Each sample should be taken to the laboratory immediately. Glucose and hGH are measured in each sample.

How to Prepare:
Fast and limit physical activity for 10 to 12 hours before the test,. or the test results may be altered.

If you or your child is taking medications, your health care provider may ask that you withhold these before the test, as some can affect results.

You will be asked to relax for at least 90 minutes before the test, as exercise or increased activity can alter hGH levels.

Inform your health care provider if you or your child has had a radioactive scan performed within a week of this test, as radioactive scans can affect test results.

If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.

How it Feels:
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 .

Risks:
Risks associated with venipuncture are slight:
  • excessive bleeding
  • fainting or feeling lightheaded
  • hematoma (blood accumulating under the skin)
  • infection (a slight risk any time the skin is broken)
  • multiple punctures to locate veins



Why this Test is Performed:
This test is a screen for elevated levels of hGH, a condition that leads to gigantism in children and acromegaly in adults. This is not a normal screening tool, rather a test that is performed if you show signs of increased hGH.

Normal Values:
Normal test results would reveal an hGH level of less than 3 ng/ml. In children, if the second blood sample is taken after the second hour, there may be increased levels from a rebound phenomenon die to the occurrence of reactive hypoglycemia .

Abnormal Results:
If the hGH levels are unaltered and remain high during the suppression test, then gigantism or acromegaly is suspected. The test may need to be confirmed by retesting at the same time, under the same conditions another day.

Cost:
Information not available.

Special Considerations:
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.