An angiocatheter (IV) is usually placed in a vein (venipuncture), typically 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 then removed while the angiocatheter is left in the vein. The tourniquet is then removed to restore circulation.

Your blood will be drawn 5 times. To prevent multiple punctures of the vein, blood samples will be taken through the IV instead of by venipuncture. Sometime between 6 and 8 a.m. the first sample is drawn, then an intravenous (IV) infusion of arginine is started and continued for 30 minutes. After the 30-minute infusion, four blood samples are drawn at 30-minute intervals and sent immediately to the lab.

Fast and limit physical activity for 10 to 12 hours before the test or test results may be altered and invalidated.

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. This test requires temporary placement of an angiocatheter, an IV, and this should be explained to your child. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.

When the needle is inserted, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is typically performed on infants and children to identify hGH deficiency as a cause of growth retardation. It is also useful in detecting a pituitary tumor.

A normal response is at least 10 ng/mL peak value; 5–10 ng/mL is indeterminate; 5 ng/mL is subnormal. (A normal value rules out GH deficiency; in some laboratories, the normal level is 7 ng/mL.)

Note: ng/ml = nanogram per milliliter.

Failure of the arginine infusion to raise hGH indicates there is a diminished amount of hGH in the anterior pituitary where is it stored. In children, this results in dwarfism; in adults, it may be associated with panhypopituitarism.

About 10 to 15% of people with normal functioning pituitaries may fail to respond on the first test. If hGH fails to reach 10 ng/ml during the test, then the test should be repeated at the same time on another day or tested with other stimuli.

Risks associated with venipuncture 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 or inserting an IV may be more difficult in you or your child than in others.