Growth hormone (GH) is a protein produced by the pituitary gland. It helps your bones and muscles develop properly.
For most people, GH levels naturally rise and fall during childhood and then are lower in adulthood. In some people, however, GH levels can be lower than normal. A persistent shortage of GH is known as growth hormone deficiency (GHD). The condition can cause health problems such as decreased muscle mass and slow growth.
If your doctor suspects that your body is not producing enough GH, they may order a GH stimulation test. GHD is rare in all age groups, especially adults. Testing is usually only done when there is strong evidence that a person has this condition.
In children, GHD may include symptoms such as below average height, slow growth, poor muscle development, and delayed onset of puberty.
In adults, the symptoms of GHD are somewhat different because adults have stopped growing. Symptoms in adults may include reduced bone density, muscle weakness, fatigue, and an increase in fat, especially around the waist.
Depending on the clinic or facility where you undergo a GH stimulation test, the specific procedure may vary slightly. In general, here’s what you can expect if your doctor orders a GH stimulation test for you or a family member:
Preparing for the test
Your healthcare team will instruct you not to eat for 10 to 12 hours before the test. In most cases, you must also avoid drinking any fluids except water. Gum, breath mints, and flavored water are also off-limits.
Your doctor will tell you if you need to stop taking certain medications before the test. Some medications known to affect GH levels include:
If you’re not feeling well and think you may have a viral infection, let your doctor know. They may recommend rescheduling the test.
How the test is performed
Your healthcare provider will place an IV (intravenous line) in a vein in your arm or hand. The procedure is similar to a blood test. The major difference is that a small needle connected to a tube that is part of the IV stays in your vein.
You may experience some discomfort when the needle pierces your skin, and some bruising afterward, but the risks and side effects are minimal.
Your healthcare provider will take an initial blood sample through the IV. This and all later samples will most likely be collected using the same IV line.
Then you will receive a GH stimulant through the IV. This is a substance that typically encourages an increase in GH production. Some commonly used stimulants are insulin and arginine.
Next, your healthcare provider will take several more blood samples at regular intervals. The entire procedure usually takes about three hours.
After the test, laboratory professionals will analyze your blood samples to see whether your pituitary gland has produced the expected amount of GH in response to the stimulant.
GH stimulation test costs vary based on your healthcare provider, your health insurance coverage, and the facility where you have the test. Lab fees for analyzing the test also vary.
It’s possible to buy a GH serum test directly from a lab for about $70, but this is not the same test as a GH stimulation test. A GH serum test is a blood test that only checks GH levels in the blood at one point in time.
A GH stimulation test is more complex because blood levels of GH are checked multiple times over a period of hours, before and after you take a stimulant.
Testing is generally not the most costly aspect of a GH-related condition. For those who have GHD, the bigger expense is treatment. The cost of GH replacement therapy can range between $7,500 and $10,000 per year for an average dose of 0.5 milligrams GH per day. If you have health insurance, it may cover a significant portion of the cost.
Your GH stimulation test results will show the peak concentration of GH in your blood. This concentration is expressed in terms of nanograms of GH per milliliter of blood (ng/mL). This is how the results are usually interpreted:
In general, a child whose test results show a GH concentration of 10 ng/mL or greater in response to stimulation doesn’t have GDH. If a child’s test results show a GH concentration of less than 10 ng/mL, a second GH stimulation test may be ordered.
If the results of two separate tests both show a GH concentration of less than 10 ng/mL, a doctor will likely diagnose GHD. Some healthcare facilities use a lower cutoff point to diagnose GHD, such as 7 ng/mL.
Most adults produce a GH concentration of 5 ng/mL in a GH stimulation test. If your results show a rate of 5 ng/mL or higher, in response to stimulation, you do not have GHD.
Concentrations of less than 5 ng/mL mean that GHD can’t be definitively diagnosed or ruled out. Another test may be ordered.
Severe GH deficiency is defined in adults as a peak GH concentration of 3 ng/mL or less.
You may experience some discomfort where the needle pierces your skin for the IV. It’s also common to have some small bruising afterward.
If your doctor uses cortrosyn for the test, you may experience a warm, flushing feeling in your face or a metallic taste in your mouth. Clonidine can lower your blood pressure. If it’s given during a GH stimulation test, you may feel slightly dizzy or lightheaded.
If your doctor uses arginine during the test, you may experience brief low blood pressure. This can cause feelings of dizziness and lightheadedness, too. The effects usually pass quickly and are often gone by the time you return home. Even so, it’s a good idea to avoid scheduling activities for the rest of the day following the test.
GHD is a rare condition. If your results don’t indicate GHD, your doctor will look for another possible cause for your symptoms.
If you’re diagnosed with GHD, your doctor will likely prescribe synthetic GH to supplement your body’s natural hormone levels. Synthetic GH is administered by injection. Your healthcare team will teach you how to perform these injections so that you can treat yourself at home.
Your doctor will monitor your progress and adjust the dosage as needed.
Children often experience fast, dramatic growth from GH treatments. In adults with GHD, GH treatments can lead to stronger bones, more muscle, less fat, and other benefits.
There are some known side effects of synthetic GH treatment, such as headaches, muscle pain, and joint pain. However, serious complications are rare. The risks associated with treating GHD are usually surpassed by the potential benefits.
A GH stimulation test is part of the process of diagnosing GHD. However, this condition is rare. Many people who undergo a GH stimulation test won’t be diagnosed with GHD. Even if the results of the first test suggest GHD, an additional test is needed before your doctor will make a diagnosis.
If you or your child are diagnosed with GHD, treatment with synthetic GH is highly effective. Starting treatment earlier usually leads to better outcomes. Your doctor will discuss the side effects of treatment. Generally, the benefits of treating GHD outweigh the risk of side effects for most people.