This test measures the amount of growth hormone (GH) in your blood.
GH is made in your pituitary gland. It affects height, bone, and muscle growth in children. It affects how adults feel and look, as well as their bone and muscle health.
GH is made in a pulse-like manner. Most GH is made while you sleep. When you're awake, little or possibly no GH is found in your blood. That makes it hard to test your GH level. Specialists have developed methods to figure out if you make too much or too little by testing your blood over time after you have been given a suppressing agent, such as glucose, or a stimulating agent, like insulin.
You may need this test if your doctor suspects you have a GH problem. Signs include:
Decreased bone density
Reduced muscle strength
Increased lipid levels, or fats in your blood
Acromegaly, or excessive GH disease
Your child might need this test if he or she has these signs:
Symptoms of gigantism
You may also have this test if you have been given GH treatment, so your doctor can watch your dosage and change it if needed.
You may have this test if you are a young adult who has been taking GH for years but may no longer need it.
You may also need this test if you have acromegaly, so your doctor can keep an eye on your disease.
Your doctor may also order a blood test for insulin-like growth factor-1 (IGF-1). GH tells your liver to make IGF-1, so usually GH and IGF-1 are correlated. GH is secreted in pulses while you sleep, but IGF is always found in your blood. That makes it much easier to find IGF-1 in your blood than GH.
Your doctor may also order other tests to look for a possible growth hormone deficiency. These tests include:
Tests that use other drugs like clonidine, L-dopa, or glucagon
If your doctor suspects that you have excess growth hormone, he or she may order an oral glucose tolerance test.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
If your levels are higher, it may mean you have:
Acromegaly in adults
Gigantism in children
Noncancerous pituitary gland tumor in adults
If your levels are lower, it may mean you have:
Growth hormone deficiency
Levels that are higher or lower may also be caused by chronic malnutrition, cirrhosis, and stress from surgery or a serious infection.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Certain foods and beverages, especially those high in protein, can affect your results. Certain medications, including oral contraceptives containing estrogen, can also affect your results. Great physical or emotional stress and sleeping can affect your results.
Your doctor may ask you to stop taking oral estrogens for a time before this test. You also may be told to not eat or drink anything but water for a certain amount of time before the test.
Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.