What is a Growth Hormone Stimulation Test?

Our bodies usually change quietly, almost without notice. Children grow taller. Our hair often thins as we age. It’s all part of maturing, and it’s controlled by hormones. But sometimes things go wrong.

The hormone that helps control growth and the chemical reactions in our bodies is called human growth hormone. (You may see it written as HGH, or GH for short.) Your body might make it in great amounts or not at all.

Too much or too little HGH can lead to a variety of issues, including:

• Dwarfism
• Fatigue
• Bone weakness
• Delayed puberty

If you or your child has any of these conditions, your doctor may suggest you take a growth hormone stimulation test. The basis of this test is a simple blood sample, which is then looked at in a lab.

Though growth hormone issues can cause problems if left untreated, treating them may be as simple as a regular injection of growth hormone. And in children, these issues may get better on their own over time.

Your Pituitary Gland

Growth hormone is made by the pituitary gland. It’s a pea-sized gland near the center of your head, just below the front of the brain and behind your nose.

GH isn’t the only hormone made by the pituitary gland. In fact, the pituitary has been called the “master gland” because its hormones help control other hormones. It’s part of what’s called the endocrine system, which oversees many body functions.

But if too much or too little GH is in your body, there may be something wrong with your pituitary gland.

In children, you may find this out during a visit with your pediatrician.

During a typical visit, your pediatrician will likely check your child for height, weight, and head size and see how they compare with the normal range for children of that age. If the measurements are outside that range, they may order tests.

If you’re an adult, you may want to visit your doctor if your symptoms include:

• Low energy
• Less strength
• Depression
• Decline in muscle mass
• Increase in body fat

There are many different possible causes for these symptoms, but they may also signal issues with GH production. A test can measure the amount of GH in your blood.

Your pituitary gland releases GH in pulses that vary by sex, age, and even time of day. That is why doctors use different methods to stimulate or suppress the release of growth hormone before you take the test.

How to Prepare Your Child for the Test

Several tests may be needed to see if your child has a growth hormone deficiency. Some involve the measurement of different hormones with simple blood tests. The growth hormone stimulation uses one or two different medications to “stimulate” or raise the amount of GH released by their body. Then your doctor can see how much the child's body is making. There are a number of things that may be required and helpful before your child takes the test:

Avoid medications: They shouldn't take certain medications the night before and the day of the test unless your doctor or nurse has permitted them. One of the medicines that may be used, such as clonidine, doesn’t mix with medications such as amphetamine and dextroamphetamine (Adderall) or methylphenidate (Ritalin), so your doctor will give you instructions on whether you need to make any changes with them before the test.

Be ready to pass the time: Since the test takes a few hours, bring books, videos, or other distractions to keep your child from getting bored. Be sure they wear comfortable clothes.

How Adults Can Prepare

Your doctor will typically ask you to take more than one kind of test.

You may need the stimulation test, as well as some of these other tests:

• The IGF-1 and IGFBP-3 tests, which check the amount of a different but related hormones
• Tests to check for issues with other hormones, including cortisol, prolactin, and testosterone

Children will also typically get a combination of these tests.

If you need to take a growth hormone stimulation test, you may need to:

Fast: Some medical experts recommend up to 12 hours without food before the test. Talk to your doctor about this beforehand to find out what you should do in your case.

Avoid certain medications: These include insulin, birth control pills, and the herb St. John’s wort. If you take these or any other medicines, talk to your doctor to see what you need to do.

Don’t exercise: Workouts 10 hours or less before the test can throw off resting hormone levels.

Testing takes up to 3 hours, so you should also dress comfortably and bring a book or some entertainment.

Low blood sugar and obesity may skew results, so talk with your doctor if you have these conditions.

What Happens During the Test?

For your child, the test begins with a technician placing an IV line in their arm or hand.

After giving a blood sample, your child will get a dose of medicine or medicines to stimulate the pituitary gland to release growth hormone. The most common medicines chosen are clonidine (Catapres), arginine or glucagon. Insulin is less commonly used now because of safety concerns with children.

During all of this, the assistant will probably take a blood sample around every 30 minutes. The samples are not large -- perhaps a couple of teaspoons, total, over the course of the day.

At the end of the test, your child can eat. They should rest afterwards.

It’s a similar process for adults who get the GH stimulation test. Adults have the option of a medicine called macimorelin (Macrilen)which is given as a liquid to drink. Insulin is less often used now because of unpleasant side effects and safety concerns due to low blood sugars.

Both children and adult blood samples can also be checked for IGF-1 and IGFBP-3 alongside the stimulation test.

If you take the GH suppression test, you’ll drink a glucose solution in the first 5 minutes, and get your blood checked every 30 minutes for 2 hours.

Growth hormone tests aren’t likely to cause any complications, though some people may feel faint. Bruising is possible where the IV line went into your vein.

What the Results Mean

Test results should be ready in several days.

High levels of GH may suggest:

• Possible acromegaly
• Gigantism (in children, it can cause really long bones, delayed puberty, and other problems)
• A tumor

Low levels may indicate:

• Possible dwarfism
• Slow growth
• Hypopituitarism, which means your pituitary gland isn’t working as well as it should.

Because GH issues may be related to other glands, such as the thyroid, your doctor may recommend that you get more tests. If your doctor suspects a tumor, they may ask you to get an MRI, CT scan, or X-ray.

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