This test measures the level 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 look and feel, 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 GH by testing your blood over time after suppressing GH production.
Most people with too much GH have a noncancerous tumor in their pituitary gland. The tumor also produces GH, and this test helps your doctor find out if you have a tumor. For the test, you are given glucose, which makes your pituitary stop making GH, and your blood is drawn every 30 minutes for two hours. The tumor will keep on making GH, so the amount of GH in your blood will stay the same.
You may need this test if your doctor suspects that you have acromegaly, or excessive growth hormone disease. Acromegaly is a disorder in adults caused by too much GH. Other disorders caused by too much GH are growth hormone hypersecretion syndrome and anterior pituitary adenoma syndrome.
In children, acromegaly is called gigantism. Your child may need this test if the doctor suspects that he or she might have gigantism.
Gigantism and acromegaly have many characteristics that develop slowly. Not everyone has every symptom. Signs and symptoms include:
Accelerated growth in children
Enlarged head, with specific changes in facial features, such as an enlarged jaw, a widened nasal bridge, a protruding forehead, and space between the teeth
Enlarged hands and feet
You may also have this test if you have been diagnosed with acromegaly, to help your doctor keep an eye on your disease.
You may have this test if you have been given treatment to decrease GH production, so your doctor can watch your dosage and change it if needed.
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 GH and IGF-1 are usually 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 such as an oral glucose tolerance test to see if your GH is higher than normal.
Your doctor may also check the levels of other hormones including:
Growth-hormone-releasing hormone, or GHRH
Luteinizing hormone, or LH
Follicle-stimulating hormone, or FSH
Thyroid-stimulating hormone, or TSH
Corticotropin, or ACTH
Your doctor may also order an MRI to check for a pituitary tumor.
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.
Results are given in nanograms per milliliter (ng/mL). Normal GH levels should drop to less than 1 or 2 ng/mL after you are given glucose.
If you have higher levels of growth hormone, it means you may have:
Acromegaly in adults
Gigantism in children
Noncancerous pituitary tumor
Nonpituitary tumor, in very rare cases
Higher levels of GH 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.
In addition, 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.