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IGF-1

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Also known as: Somatomedin C
Formal name: Insulin-like Growth Factor - 1
Related tests: Growth Hormone, Growth Hormone Releasing Hormone, Glucose Tests, Glucose Tolerance Test, Free T4, TSH, IGFBP-3

At a Glance

Why Get Tested?

To help diagnose growth hormone (GH) deficiency or, less commonly, growth hormone excess; to evaluate pituitary function; to monitor the effectiveness of GH treatment

When to Get Tested?

When a child has signs and symptoms of slow growth, short stature, and delayed development or an adult has decreased bone density, reduced muscle strength, and increased lipids that suggest insufficient GH and IGF-1 production; when a child or adult has signs and symptoms of gigantism or acromegaly, respectively, that suggest excess GH and IGF-1 production; during and after treatment for GH abnormalities; when a pituitary disorder is suspected

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?

Insulin-like growth factor-1 (IGF-1) is a hormone that, along with growth hormone (GH), helps promote normal bone and tissue growth and development. The test measures the amount of IGF-1 in the blood.

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. Since GH is released into the blood in pulses throughout the day, it is difficult to interpret the results from a single GH test. IGF-1 mirrors GH excesses and deficiencies, but unlike GH, its level is stable throughout the day. This makes IGF-1 a useful indicator of average GH levels. The IGF-1 test is therefore often used to help evaluate for GH deficiency or GH excess.

IGF-1 levels, like GH, 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 a dysfunctional pituitary gland with decreased pituitary hormones (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.

IGF-1 deficiencies early in life, usually the result of GH deficiency, 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 density, less muscle mass, and altered lipid levels. However, testing for IGF-1 deficiency, or GH 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 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 two rare conditions, 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 lifespan.

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

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Kaneshiro, N. (Updated 2013 August 22). Short stature. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003271.htm through http://www.nlm.nih.gov. Accessed August 2014.

Diaz-Thomas, A. et. al. (Updated 2014 May 12)). Gigantism and Acromegaly. Medscape Drugs & Diseases [On-line information]. Available online at http://emedicine.medscape.com/article/925446-overview through http://emedicine.medscape.com. Accessed August 2014.

Eledrisi, M. (Updated 2013 October 17). Growth Hormone Deficiency. Medscape Drugs & Diseases [On-line information]. Available online at http://emedicine.medscape.com/article/120767-overview through http://emedicine.medscape.com. Accessed August 2014.

Rosenbloom, A. and Guevara-Aguirre, J. (Updated 2014 January 23). Growth Hormone Resistance. Medscape Drugs & Diseases [On-line information]. Available online at http://emedicine.medscape.com/article/922902-overview through http://emedicine.medscape.com. Accessed August 2014.

Meikle, A. W. (Updated 2014 January). Growth Hormone Deficiency. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/GrowthHormone.html?client_ID=LTD#tabs=0 through http://www.arupconsult.com. Accessed August 2014.

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Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Thorner, M. et. al. (2003 September 24). Advanced Strategies for Achieving IGF-I Control in Acromegaly. The Endocrine Society [CME on Medscape]. Available online at http://www.medscape.com/viewprogram/2638_pnt through http://www.medscape.com.

Cromie, W. (1999 April 22). Growth Factor Raises Cancer Risk. Harvard Gazette Archives [On-line article]. Available online at http://www.news.harvard.edu/gazette/1999/04.22/igf1.story.html through http://www.news.harvard.edu.

IGF-1 (Insulin-Like Growth Factor 1). ARUP Guide to Clinical Laboratory Testing. [On-line information]. Available online at http://www.arup-lab.com/guides/clt/tests/clt_al3b.jsp#1349162 through http://www.arup-lab.com.

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Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 879 880.

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.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 626-628.

Sheppard, M. (2007 April 3). Growth Hormone Assay Standardization: An Important Clinical Advance. Medscape from Clin Endocrinol. 2007;66(2):157-161. [On-line information]. Available online at http://www.medscape.com/viewarticle/553885 through http://www.medscape.com. Accessed 8/18/07.

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William E. Winter, MD, FACB. Lab Tests Online adjunct board member.

(© 1995-2010). Unit Code 15867: Insulin-Like Growth Factor 1 (IGF-1), Serum. Mayo Clinic, Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/15867 through http://www.mayomedicallaboratories.com. Accessed October 2010.

Meikle, W. and Roberts, W. (Updated 2010 May). Growth Hormone Deficiency. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/GrowthHormone.html?client_ID=LTD through http://www.arupconsult.com. Accessed October 2010.

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Savage, M. et. al. (2010 June 23). The Continuum of Growth Hormone–IGF-I Axis Defects Causing Short Stature: Diagnostic and Therapeutic Challenges. Medscape Today from Clin Endocrinol. 2010;72(6):721-728. [On-line information]. Available online at http://www.medscape.com/viewarticle/722763 through http://www.medscape.com. Accessed October 2010.

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