At a Glance
Why Get Tested?
To identify diseases and conditions caused by either a deficiency or overproduction of growth hormone (GH), to evaluate pituitary function, and to monitor the effectiveness of treatment for excess production of GH
When to Get Tested?
When slow growth in stature, delayed maturational development (in children), decreased bone density and/or muscle strength, and increased lipids (in adults) could be related to insufficient GH production; when a person has symptoms suggestive of gigantism (in children) or acromegaly (in adults) that may be a result of excess GH production; as part of an evaluation of pituitary function
Usually several blood samples, drawn at timed intervals from veins in your arm; sometimes a single sample of blood, drawn following a fast and rest or after a period of strenuous exercise
Test Preparation Needed?
Follow any instructions you are given, such as to fast, in order to prepare for this test.
The Test Sample
What is being tested?
This test measures the amount of growth hormone (GH) in the blood. GH is a hormone produced by the pituitary gland, a grape-sized gland located at the base of the brain behind the bridge of the nose. It is normally secreted into the bloodstream in pulses throughout the day and night with peaks that occur mostly during the night.
Growth hormone is essential for a child's normal growth and development and promotes proper linear bone growth from birth through puberty. Children with insufficient GH production grow more slowly and are smaller in size for their age. Excess GH is most often due to a GH-secreting pituitary tumor (usually benign). Too much GH can cause children's long bones to continue to grow beyond puberty, resulting in gigantism with heights of 7 or more feet tall. Those with excess GH may also have thickening of facial features, general weakness, delayed puberty, and headaches. Gigantism is an extremely rare condition.
Although GH is not as active in adults, it does play a role in regulating bone density, muscle mass, and lipid metabolism. Deficiencies can lead to decreased bone densities, less muscle mass, and altered lipid levels. However, testing for GH deficiency is not routine in adults who have decreased bone density and/or muscle strength or increased lipids. GH deficiency is only a very rare cause of these disorders.
Excess GH in adults can lead to acromegaly, marked not by bone lengthening but by bone thickening. Although symptoms such as skin thickening, sweating, fatigue, headaches, and joint pain can be subtle at first, increased GH levels can lead to enlarged hands and feet, enlarged facial bones, carpal tunnel syndrome, and abnormally enlarged internal organs. Excess GH can also cause skin tags and intestinal polyps. If untreated, acromegaly and gigantism can lead to complications such as type 2 diabetes, increased risk of cardiovascular disease, high blood pressure, arthritis, and in general, a decreased life span.
GH stimulation and suppression tests are most often used to diagnose GH abnormalities. Since growth hormone is released by the pituitary gland in bursts throughout the day, random measurements of GH levels are not usually clinically useful.
How is the sample collected for testing?
Usually GH suppression or stimulation testing is done. After fasting for 10 to 12 hours, a blood sample is drawn from a vein in the arm. Then, under medical supervision, a person is given either a solution to drink or an intravenous (IV) solution through a vein in the arm. Blood samples are then drawn from veins (or from the IV) at timed intervals.
Sometimes, a single sample of blood is drawn following a fast and rest or after a period of strenuous exercise.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Follow any instructions you are given. In most cases, a person should be fasting. Resting or strenuous exercise for a time period before collection may be required.
Children and early adolescents who are being tested for GH deficiency should be prepared for treatment with sex steroids for a few days prior to testing. Such treatment reduces the number of falsely low GH responses to stimuli. The doctor who is ordering the GH testing should provide the child's parents with a prescription for such medications. Some doctors will also prescribe propranolol prior to testing to reduce the number of falsely low GH responses to stimulation.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
William E. Winter, MD, FACB. Lab Tests Online adjunct board member.
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