Growth hormone (GH) is one of several hormones produced by the pituitary gland in your brain. It’s also known as human growth hormone (HGH) or somatotropin.
GH plays a crucial role in human growth and development, especially in children and adolescents. GH levels that are higher or lower than they should be can lead to health problems in both children and adults.
If your doctor suspects that your body may be producing too much or too little GH, they’ll typically start by ordering tests to measure the levels of GH in your blood. Identifying any issues related to GH will help your doctor make a diagnosis and determine the best course of treatment for you.
There are several different types of GH tests, and the specific testing protocol varies depending on which test your doctor orders.
As with all medical tests, it’s important to follow all of the preparation instructions from your healthcare team. In general, for GH tests, your doctor will ask you to:
- fast for a specific period of time before the test
- stop taking the vitamin biotin, or B7, at least 12 hours before the test
- stop taking certain prescription medications a few days before the test, if they might interfere with the test results
For some tests, your doctor may provide additional preparation instructions.
It’s uncommon for people to have GH levels outside the typical range, so GH tests aren’t performed routinely. If your doctor thinks the levels of GH in your body may be abnormal, they’ll likely order one or more of the following tests.
GH serum test
A GH serum test can measure the amount of GH in your blood. For this test, a healthcare professional will use a needle to collect a sample of your blood — in short, it’s much the same as any other blood test.
The blood sample will be sent to a lab for analysis. The results of a GH serum test let your care team know the level of GH in your blood at the time when your blood sample was taken.
But this may not offer enough information to help your doctor make a diagnosis since levels of GH in your body naturally rise and fall throughout the day.
Insulin-like growth factor-1 test
Your doctor may order an insulin-like growth factor-1 test (IGF-1 test) at the same time as a GH serum test. If you have an excess or a deficiency of GH, you’ll also have higher- or lower-than-normal levels of IGF-1.
The key advantage of examining IGF is that, unlike GH, its levels remain stable. You’ll only need to give one blood sample for both tests.
The GH serum and IGF-1 tests don’t usually provide your doctor with enough information to make a diagnosis. These tests generally serve more of a screening purpose. In other words, they help your care team determine whether you need further tests.
If your doctor suspects that your body is producing too much or too little GH, they’ll most likely order either a GH suppression test or a GH stimulation test.
GH suppression test
A GH suppression test helps your doctor confirm if your body produces too much GH.
For this test, a healthcare professional will use a needle or IV to take a blood sample. Next, they’ll ask you to drink a sweet solution containing glucose, a type of sugar.
You’ll then give a few more samples of blood at timed intervals during the 2 hours after you drink the solution. These samples will be sent to a lab for analysis.
In most people, glucose lowers GH production. The lab will check your hormone levels against expected levels at each testing interval.
GH stimulation test
A GH stimulation test helps your doctor diagnose an excess or deficiency in GH production.
For this test, a healthcare professional will generally use an IV to take an initial blood sample. They’ll then give you a medication that triggers your body to release GH. The healthcare professional will monitor you and take several more blood samples at timed intervals over 2 hours.
The samples will be sent to a lab and compared with the expected GH levels at each interval after taking the medication.
The cost of GH tests varies based on your insurance coverage, the facility where you have the tests done, and the lab used to perform the analysis.
The simplest tests are the GH serum and IGF-1 tests, which only require a blood draw. The typical cost for each of these tests is about $70 if ordered directly from a lab. Your actual costs may vary depending on how much your healthcare team charges for services, like drawing your blood and sending it to the lab.
Your doctor will receive your lab results and interpret them. In general, the results of a GH serum test and an IGF-1 test don’t provide enough information to diagnose a disorder related to GH. If your test results indicate that you may have a GH-related condition or need further testing, your doctor’s office will usually:
- contact you for a follow-up appointment
- order a GH suppression test
- order a GH stimulation test
If your suppression test reveals a high GH level, this could mean:
- your glucose didn’t lower your GH production as expected
- you might have an overproduction, if the IGF-1 level was also high
- you may need additional tests to determine the cause
If your GH stimulation test results indicate low hormone levels, this could mean:
- your body didn’t release as much GH as expected
- you have a GH deficiency, if your IGF-1 level was also low
- your doctor may recommend additional testing
The range for normal results may vary depending on the lab or your healthcare professional. Generally, normal GH test results are:
- below 0.3 nanograms per milliliter (ng/mL) for suppression tests
- peak concentration above 4 ng/mL for stimulation tests in adults
- peak concentration above 5 ng/mL for stimulation tests in children
Results above this range could suggest your body produces too much growth hormone. That said, some guidelines favor a peak concentration above
Jennifer Osipoff, MD, a pediatric endocrinologist with Stony Brook Children’s Hospital, says that growth hormone is secreted from the pituitary gland mainly during sleep. Still, this secretion also occurs in small spurts throughout the day.
“As such, a random GH level is not a clinically relevant value if assessing for growth hormone deficiency or excess,” Osipoff said. “Instead, endocrinologists will measure insulin-like growth factor 1 (IGF-1), a protein that is made in response to GH secretion.”
Providers break passing levels down into two groups: pediatric patients under 18 and adult patients 18 and over.
|Under 18||GH stimulation||peak concentration greater than 10 ng/mL or 5 ng/mL, depending on guidelines|
|Under 18||GH suppression||peak concentration less than 1 ng/mL|
|18 and older||GH stimulation||peak concentration greater than 4 ng/mL|
|18 and older||GH suppression||peak concentration less than 1 ng/mL|
Both adults and children can undergo growth hormone testing. Yet healthcare professionals may recommend this testing for different reasons, depending on age.
|Reason for testing||Issues with GH deficiency||Issues with excess GH||Likelihood of GH abnormality|
|Children||GH deficiency or excess GH||• delayed growth and bone development|
• delayed puberty
• below average height
|Adult||GH deficiency or excess GH||• reduced bone density and muscle mass|
• abnormal cholesterol
GHD is rare, and it doesn’t usually explain a child’s short stature or slow growth. A child may have below-average height for many reasons, including simple genetics.
Slow growth is also common for children, especially right before puberty. Children with a GH deficiency often grow under 2 inches per year.
A healthcare professional may also recommend GH testing if they notice signs a child’s body is producing too much GH. For example, this can happen with a rare condition known as gigantism, which causes the long bones, muscles, and organs to grow excessively in childhood.
Adult bodies rely on GH to maintain muscle mass and bone density and regulate metabolism.
If you make too little GH, you may have reduced bone density and muscle mass. A routine blood test called a lipid profile may show changes in the levels of fat in your blood. But GH deficiency is rare.
Extra GH in adults can cause a rare condition called acromegaly, which makes the bones thicken. If left untreated, acromegaly can cause a number of complications, including a higher risk of arthritis and heart problems.
GH levels that are too high or too low can indicate serious health concerns, including delayed growth and reduced bone density. Keep in mind, though, that GH-related conditions are rare.
A healthcare professional may order testing to check your GH levels using a GH suppression or stimulation test. If your test results show unusual GH levels, your care team will most likely order further testing.
If you’re diagnosed with a GH-related condition, a doctor or other healthcare professional can offer more guidance on the best course of treatment. They may, for example, prescribe synthetic GH to treat GH deficiencies. Early detection can increase your chances of a good outcome for both adults and children.