Growth hormone stimulation test

Definition

The growth hormone (GH) stimulation test measures the level of growth hormone (GH) in the blood after you receive medication that triggers the release of GH, such as arginine or GH-releasing hormone. The test measures the ability of the pituitary gland to release GH.

See also:

• Growth hormone deficiency
• Short stature

Alternative Names

Arginine test; Arginine-GHRH test

How the test is performed

The site is cleaned with germ-killing medicine (antiseptic). An IV is usually placed in a vein, typically in the inside of the elbow or the back of the hand.

The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The needle is removed while the IV is left in the vein. The elastic band is removed from your arm.

Your blood will be drawn five times. To prevent many punctures of the vein, samples will be taken through the IV line instead of re-inserting the needle each time.

The first sample will be drawn between 6 a.m. and 8 a.m. Then you will receive arginine through a vein for 30 minutes. After the 30-minute infusion, GH-releasing hormone is given to you through a vein. Then four more blood samples are drawn, once every 30 minutes.

Sometimes arginine or GH-releasing hormone is given alone for this test. Which form of the test is used depends on your health care provider's preferences.

Let your doctor know if you have severe kidney or liver disease, because an infusion of arginine could be risky for you.

How to prepare for the test

Do not eat and limit physical activity for 10 - 12 hours before the test to avoid changing the results.

Your health care provider may ask that you stop taking certain medications before the test, as some medications can affect results. (Do not stop taking any medications without first talking to your health care provider.)

You will be asked to relax for at least 90 minutes before the test, because exercise or increased activity can change GH levels.

If your child is going 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 of 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 determine whether GH deficiency is causing slowed growth.

Normal Values

• Normal peak value -- at least 10 ng/mL
• Indeterminate -- 5 - 10 ng/mL
• Subnormal -- 5 ng/mL

(A normal value rules out hGH deficiency; in some laboratories, the normal level is 7 ng/mL.)

Note: ng/mL = nanogram per milliliter.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

If this test does not raise GH levels, there is a reduced amount of hGH stored in the anterior pituitary.

In children, this results in growth hormone deficiency. In adults, it may be associated with panhypopituitarism or adult growth hormone deficiency.

What the risks are

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.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations

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References

Melmed S, Kleinberg D. Anterior pituitary. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, PA: Saunders Elsevier; 2008:chap 8.

Reiter EO, Rosenfeld RG. Normal and aberrant growth. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 23.