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Also known as: Somatomedin C
Formal name: Insulin-like Growth Factor - 1
Related tests: Growth Hormone (GH), Glucose, Glucose Tolerance Test, IGFBP-3 (IGF-Binding Protein 3)

At a Glance

Why Get Tested?

To identify diseases and conditions caused by deficiencies and overproduction of growth hormone (GH), to evaluate pituitary function, and to monitor the effectiveness of GH treatment

When to Get Tested?

When you have symptoms of slow growth, short stature, and delayed development (in children) or decreased bone density, reduced muscle strength, and increased lipids (in adults) that suggest insufficient GH and IGF-1 production; when you have symptoms of gigantism (in children) or acromegaly (in adults) that suggest excess GH and IGF-1 production; during and after treatment for GH abnormalities; as part of an evaluation of pituitary function

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Generally none, unless instructed to fast

The Test Sample

What is being tested?

The insulin-like growth factor-1 (IGF-1) test is an indirect measure of the average amount of growth hormone (GH) being produced by the body. IGF-1 and GH are polypeptide hormones, small proteins that are vital for normal bone and tissue growth and development. GH is produced by the pituitary gland, a grape-sized gland located at the base of the brain behind the bridge of your nose. GH is secreted into the bloodstream in pulses throughout the day and night with peaks that occur mostly during the night. IGF-1 is produced by the liver and skeletal muscle as well as many other tissues in response to GH stimulation. IGF-1 mediates many of the actions of GH, stimulating the growth of bones and other tissues and promoting the production of lean muscle mass. IGF-1 mirrors GH excesses and deficiencies, but its level is stable throughout the day, making it a useful indicator of average GH levels.

Like GH, IGF-1 levels are normally low in early childhood, increase gradually during childhood, peak during puberty, and then decline in adult life. Deficiencies in GH and IGF-1 may be caused by conditions such as hypopituitarism or by the presence of a non-GH-producing pituitary tumor that damages hormone-producing cells. Deficiencies in IGF-1 also occur where there is a lack of responsiveness to GH. This insensitivity may be primary (genetic) or secondary to conditions such as malnutrition, hypothyroidism, sex hormone deficiency, and chronic diseases. Genetic GH insensitivity (GH resistance) is very rare.

Deficiencies early in life can inhibit bone growth and overall development and can result in a child with a shorter than normal stature. In adults, decreased production can lead to low bone densities, less muscle mass, and altered lipids. However, testing for GH deficiency or IGF-1 deficiency is not routine in adults who have decreased bone density and/or muscle strength, or increased lipids. GH deficiency and consequent IGF-1 deficiency is only a very rare cause of these disorders.

Excess GH and IGF-1 can cause abnormal growth of the skeleton and other signs and symptoms characteristic of gigantism and acromegaly. In children, gigantism causes bones to grow longer, resulting in a very tall person with large feet and hands. In adults, acromegaly causes bones to thicken and soft tissues, such as the nose, to swell. Both conditions can lead to enlarged organs, such as the heart, and to other complications such as type 2 diabetes, increased risk of cardiovascular disease, high blood pressure, arthritis, and a decreased life span. The most common reason for the pituitary to secrete excessive amounts of GH is a GH-producing pituitary tumor (usually benign). Frequently, the tumor can be surgically removed and/or treated with drugs or radiation. In most cases, this will cause GH and IGF-1 levels to return to normal or near normal levels.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

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?

In general, no test preparation is needed; however, since this test may be performed at the same time as others, fasting for at least 12 hours may be required.

The Test

Common Questions

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Article Sources

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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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Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry. AACC Press, Washington, DC. Grenache, D and Willis, M., Chapter 31, Hypothalamic, Pituitary, and Gonadal Disorders. Pp 351-363.

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(2007 April). Acromegaly. NIDDK, NIH Publication No. 02-3924 [On-line information]. Available online at http://www.niddk.nih.gov/health/endo/pubs/acro/acro.htm through http://www.niddk.nih.gov. Accessed September 2007.