Test Overview

Human growth hormone (GH) is produced by the pituitary gland. It is essential for growth and plays an important role in how the body uses food for energy (a process called metabolism). The amount of GH in the blood changes throughout the day and is affected by exercise, sleep, emotional stress, and diet.

Too much GH during childhood can result in excessive growth (gigantism). Too little GH during childhood can inhibit growth (dwarfism). However, gigantism and dwarfism can be treated if discovered early.

In adults, excess GH is usually caused by a noncancerous tumor of the pituitary gland called an adenoma. Excess GH can lead to an abnormal bony enlargement of the face, jaw, hands, and feet (acromegaly).

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

This test is done on a blood sample taken from a vein. Two blood samples (taken 1 day apart) may be collected.

Why It Is Done

A test for growth hormone (GH) is done to:

Determine whether a child whose growth is abnormal has dwarfism or gigantism.
Help determine whether an adult has acromegaly, a condition usually caused by a GH-secreting tumor of the pituitary gland (called an adenoma).
Monitor treatment that involves use of GH.
How To Prepare

Since physical activity can interfere with GH test results, you may be asked to sit quietly for 15 to 60 minutes before your blood is drawn.

Certain medications can interfere with GH test results, such as corticosteroids and estrogen (including birth control pills). Your doctor may instruct you to stop taking these medications prior to this test. Talk to your doctor about whether these medications need to be stopped prior to the test.

How It Is Done

Because the blood levels of growth hormone (GH) can change quickly, more than one blood sample may be taken on different days. Insulin-like growth factor 1 (IGF-1) levels change more slowly and may be used as an additional test.

The health professional drawing blood will wrap an elastic band around your upper arm to temporarily stop the flow of blood through the veins of your arm. This makes it easier to put the needle into a vein properly because the veins below the band get larger and do not collapse easily.

The site where the needle will be inserted is cleaned with alcohol, and then the needle is inserted into the vein. More than one needle stick may be needed if the needle does not get placed correctly or if the vein cannot supply enough blood.

When the needle is properly placed in the vein, a collection tube will be attached to the needle and blood will flow into it. Sometimes more than one tube of blood is collected.

When enough blood has been collected, the band around your arm will be removed. A gauze pad or cotton ball is placed over the puncture site as the needle is withdrawn. Pressure is applied to the puncture site for several minutes and then a small bandage is often placed over it.

How It Feels

You may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. However, many people do not feel any pain (or have only minor discomfort) once the needle is positioned in the vein. The amount of pain you feel depends on the skill of the health professional drawing the blood, the condition of your veins, and your sensitivity to pain.

Risks

There is very little risk of complications from having blood drawn from a vein. You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.

Rarely, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.

Continued bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medications can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medication, tell the health professional before your blood is drawn.

Test Results

Normal
Normal results may vary from lab to lab.

Greater-than-normal values may mean

High growth hormone (GH) values may indicate gigantism or acromegaly. These conditions are often the result of a noncancerous tumor in the pituitary gland (adenoma). High GH values may be associated with increased insulin-like growth factor 1 (IGF-1) levels.
Increased GH levels may also result from diabetes, kidney disease, or starvation. These conditions, unlike gigantism or acromegaly, are not associated with increased IGF-1 levels.

What Affects the Test

• High levels of growth hormone (GH) can be caused by such medications as amphetamines, estrogens (including birth control pills), levodopa (Larodopa, Dopar), methyldopa (Aldomet), propranolol (Inderal), and bromocriptine (Parlodel).
• Low blood sugar can cause high GH levels.
• Low levels of GH may be caused by chlorpromazine (Thorazine) and corticosteroids.
• Rough handling, contamination, or inadequate refrigeration of the blood sample can cause inaccurate test results.

What To Think About

Newer, more sensitive tests are being developed to measure human growth hormone (GH).
Since normal levels of GH can vary widely, other tests may be done to confirm the results of a GH test. Additional tests can determine whether low levels of GH (which can be normal) mean the pituitary gland is not functioning.
Insulin-like growth factor 1 (IGF-1) blood levels are commonly evaluated along with GH levels. A high level of IGF-1 along with a high level of GH is almost always diagnostic of acromegaly. In this case, magnetic resonance imaging (MRI) studies should be done to evaluate the pituitary gland. For more information, see the medical test 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 liquid containing a large amount of sugar (glucose). Normally, the amount of GH drops to less than 1 ng/mL after drinking the glucose. Levels of GH that remain high may indicate acromegaly.
The growth hormone stimulation test (also called the insulin tolerance test) measures the level of GH in the blood before and after insulin is given through a vein (intravenously). Normally, the amount of GH increases after the insulin is given (in children the level should be more than 10 ng/mL; in adults it should be more than 7 ng/mL). A GH level that does not increase may indicate a GH deficiency. Growth hormone levels of 0 ng/mL can be found in people with GH deficiency as well as in people with normal pituitary function. For this reason, a growth hormone stimulation test can help diagnose GH deficiency.