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 normal 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 will order 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 are not performed routinely. If your doctor thinks the levels of GH in your body may be abnormal, they will likely order one or more of the following tests.
GH serum test
A GH serum test is used to measure the amount of GH in your blood when the blood is drawn. For the test, a healthcare professional will use a needle to collect a sample of your blood. The test itself is fairly routine and carries little discomfort or risk.
The blood sample will be sent to a lab for analysis. The results of a GH serum test show your doctor the level of GH in your blood at the single point in time when your blood sample was taken.
However, this may not be enough information to help your doctor make a diagnosis because levels of GH in your body naturally rise and fall throughout the day.
Insulin-like growth factor-1 test
An insulin-like growth factor-1 test (IGF-1 test) is often ordered at the same time as a GH serum test. If you have an excess or a deficiency of GH, you will 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. Only one blood sample is required 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 are usually used for screening, so that your doctor can decide if further tests are needed. If your doctor suspects that your body is producing too much or too little GH, they will 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. Then you will be asked to drink a standard solution containing glucose, a type of sugar. This will taste slightly sweet and may come in different flavors.
A healthcare professional will draw several more samples of your blood at timed intervals during the two 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. Then they will 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 two hours.
The samples will be sent to a lab and compared with the expected GH levels at each time point after taking the stimulant.
The cost of GH tests varies based on your insurance coverage, the facility where you have the tests done, and which lab is 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, such as drawing your blood and sending it to the lab.
Your doctor will receive your lab results and interpret them. If your test results indicate that you may have a GH-related condition or if you require further testing, your doctor’s office will usually contact you for a follow-up appointment.
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 the results are unusual, your doctor will likely order GH suppression or stimulation tests.
If your GH level during a suppression test is high, it means that the glucose didn’t lower your GH production as expected. If your IGF-1 was also high, your doctor might diagnose an overproduction of GH. Because conditions related to growth hormone are rare and can be challenging to diagnose, your doctor might suggest additional tests.
If your hormone levels during a GH stimulation test are low, your body didn’t release as much GH as expected. If your IGF-1 level was also low, it may indicate a GH deficiency. Again, your doctor will likely recommend further testing to be certain.
For suppression tests, results below 0.3 nanograms per milliliter (ng/mL) are considered the normal range, according to the Mayo Clinic. Anything higher suggests that your body may be producing too much growth hormone.
For stimulation tests, a peak concentration above 5 ng/mL in children and above 4 ng/mL in adults is generally considered in the normal range.
However, the range for normal results may vary depending on the lab and your healthcare provider. For example, some guidelines favor a peak concentration above 10 ng/mL in children to completely rule out GH deficiency using stimulation tests.
A doctor may order GH testing for children who show signs of a GH deficiency. These include:
- delayed growth and bone development
- delayed puberty
- below average height
GHD is rare and isn’t usually the cause of a child’s short stature or slow growth. A child may be below average in height for many reasons, including simple genetics.
Times of slow growth are also common for children, especially right before puberty. Children with a GH deficiency often grow under 2 inches per year.
GH testing may also be helpful if there are signs that 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 to 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. However, GH deficiency is rare.
Extra GH in adults can cause a rare condition called acromegaly, which makes the bones thicken. 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 conditions. However, it’s important to keep in mind that these conditions are rare.
Your doctor may order testing to check your GH levels using a GH suppression or stimulation test. If your test results show unusual GH levels, your doctor is likely to order further testing.
If you’re diagnosed with a GH-related condition, your doctor will advise you on the best course of treatment. Synthetic GH is often prescribed to those with GH deficiencies. For both adults and children, early detection is important to increase the chances of a good outcome.