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Human Growth Hormone

A growth hormone (GH) test measures the amount of human growth hormone (GH) in the blood. GH is made by the pituitary gland and is needed for growth. It plays an important role in how the body uses food for energy (metabolism). The amount of GH in the blood changes during the day and is affected by exercise, sleep, emotional stress, and diet.

Too much GH during childhood can cause a child to grow larger than normal (gigantism). Too little GH during childhood can cause a child to grow less than normal (dwarfism). Both conditions can be treated if found early.

In adults, too much GH is caused by a noncancerous tumor of the pituitary gland (adenoma). Too much GH can cause bones of the face, jaw, hands, and feet to grow larger than normal (acromegaly).

Growth hormone can cause the release of other substances (factors) that affect growth and metabolism. One of these is insulin-like growth factor 1 (IGF-1). When the GH level is very high, the IGF-1 level is also very high. A test for IGF-1 may also be done to confirm high GH levels.

Why It Is Done
A test for growth hormone (GH) is done to:
See whether a child whose growth is abnormal has dwarfism or gigantism.
See whether an adult has acromegaly. This condition is caused by a tumor (adenoma) of the pituitary gland.
Check treatment that uses growth hormone.

High values
High GH values may mean gigantism or acromegaly is present. These conditions are caused by a noncancerous tumor in the pituitary gland (adenoma). Insulin-like growth factor 1 (IGF-1) levels should also be high.
High GH levels may also be caused by diabetes, kidney disease, or starvation. These conditions do not cause high IGF-1 levels.

What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
Taking medicines, such as amphetamines, corticosteroids, insulin, or estrogens.
Having low blood sugar (hypoglycemia).
Being obese.
Taking the herb St. John's wort.

What To Think About
Normal levels of growth hormone (GH) change during the day so other tests may be done to confirm the results of a GH test. Other tests can show whether low levels of GH (which can be normal) mean the pituitary gland is not working correctly.

IGF-1 blood levels are often done at the same time as a GH test. A high level of IGF-1 with a high level of GH generally means acromegaly is present. In this case, magnetic resonance imaging (MRI) is done to look at the pituitary gland. For more information, see the topic Magnetic Resonance Imaging (MRI) of the Head.

The growth hormone suppression test (also called the glucose loading test) measures the level of GH in the blood before and after a person drinks fluid with a large amount of sugar (glucose) in it. Normally, the amount of GH drops to less than 1 ng/mL after drinking the glucose. Levels of GH that stay high may mean acromegaly is present.

The growth hormone stimulation test measures the level of GH in the blood before and after insulin or arginine is given in a vein (intravenously) in the arm. No detectable growth hormone can be found for people with normal pituitary function. A growth hormone stimulation test may be used to see if a person lacks GH. Normally, the amount of GH increases after insulin or arginine. A GH level that does not increase after the insulin or arginine is given may mean the person lacks growth hormone.

Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Healthwise, Staff. "Human Growth Hormone (HGH)." Human Growth Hormone (HGH) Home 08/12/10: 1-3. Web. 9/14/11.

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