At a Glance
Why Get Tested?
When to Get Tested?
When you have documented hypoglycemia; when you have symptoms suggesting insulin either is being inappropriately released or utilized by your body; when you have diabetes and your doctor wants to monitor your insulin production; sometimes to document insulin resistance
A blood sample drawn from a vein in your arm
Test Preparation Needed?
You may be asked to fast for 8 hours before the blood sample is collected; occasionally your doctor may do the test at other times, such as when a glucose tolerance test is done. In some cases, your doctor may request that you fast longer.
The Test Sample
What is being tested?
This test measures the amount of insulin in the blood. Insulin is a hormone that is produced and stored in the beta cells of the pancreas. It is vital for the transportation and storage of glucose at the cellular level, helps regulate blood glucose levels, and has a role in lipid metabolism.
When blood glucose levels rise after a meal, insulin is released to allow glucose to move into tissue cells, especially muscle and adipose (fat) cells, where is it is used for energy production. Insulin then prompts the liver to either store the remaining excess blood glucose as glycogen for short-term energy storage and/or to use it to produce fatty acids. The fatty acids are eventually used by adipose tissue to synthesize triglycerides to form the basis of a longer term, more concentrated form of energy storage.
Without insulin, glucose cannot reach most of the body's cells. Without glucose, the cells starve and blood glucose levels rise to unhealthy levels. This can cause disturbances in normal metabolic processes that result in various disorders, including kidney disease, cardiovascular disease, and vision and neurological problems. Thus, diabetes, a disorder associated with decreased insulin effects, is eventually a life-threatening condition.
People with type 1 diabetes produce very little insulin and so eventually require insulin supplementation therapy. Type 2 diabetes is generally related to insulin resistance, which increases with time. People with type 2 diabetes may initially be managed only with lifestyle modifications such as diet and exercise. Eventually, they may require oral medications that increase the sensitivity of their body's cells to insulin or that stimulate their body to produce more insulin. Type 2 diabetics may also eventually need to use insulin injections to achieve normal glucose levels.
Insulin and glucose levels must be in balance. Hyperinsulinemia is an excess amount of insulin in the blood. Other than in insulin resistance, this is most often seen in people with insulinomas or with an excess amount of administered insulin. Hyperinsulinemia causes low blood sugar (hypoglycemia), which can lead to sweating, palpitations, hunger, confusion, blurred vision, dizziness, fainting, and seizures. Since the brain is totally dependent on blood glucose as an energy source, severe glucose deprivation due to hyperinsulinemia can lead fairly quickly to insulin shock and death.
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?
Typically, you will be asked to fast for 8 hours before blood is collected, but occasionally your doctor may do it at other times, such as when a glucose tolerance test (see Glucose) is done. In some cases, your doctor may request that you fast longer.
Ask a Laboratory Scientist
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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
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 567-568.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 290-291.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 618-619, 622-623.
Dowshen, S. (Reviewed 2009 January). Blood Test: Insulin. The Nemours Foundation, KidsHealth for Parents [On-line information]. Available online at http://kidshealth.org/parent/system/medical/test_insulin.html through http://kidshealth.org. Accessed December 2009.
Dugdale, D. and Wexler, D. (Updated 2008 August 9). Insulinoma. MedlinePlus Medical Encylopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000387.htm. Accessed December 2009.
Hussain, A. N. and Vincent, M. (Updated 2009 July 2). Diabetes Mellitus, Type 1. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/117739-overview through http://emedicine.medscape.com. Accessed December 2009.
Ligaray, K. and Isley, W. (Updated 2009 October 28). Diabetes Mellitus, Type 2. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/117853-overview through http://emedicine.medscape.com. Accessed December 2009.
(2008 November). Diabetes Overview. National Diabetes Information Clearinghouse [On-line information]. Available online at http://www.diabetes.niddk.nih.gov/dm/pubs/overview/index.htm through http://www.diabetes.niddk.nih.gov. Accessed December 2009.
(Updated 2009 August). Insulinoma. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Insulinoma.html?client_ID=LTD# through http://www.arupconsult.com. Accessed December 2009.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
MedlinePlus (2002 April 03, Updated). Insulin (Systemic). MedlinePlus Health Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/203298.html.
Hirsch, I. (1999 November 15). Type 1 Diabetes Mellitus and the Use of Flexible Insulin Regimens. American Family Physician (AAFP) [On-line Journal]. Available online at http://www.aafp.org/afp/991115ap/2343.html through http://www.aafp.org.
ARUP. Insulin, Free and Total. ARUP's Guide to Clinical Laboratory Testing (CLT) [On-line information]. Available online at http://www.arup-lab.com/guides/clt/tests/clt_a19b.htm#1837257 through http://www.arup-lab.com.
Sapin, R., et. al (2001). Elecsys Insulin Assay: Free Insulin Determination and the Absence of Cross-Reactivity with Insulin Lispro. Clinical Chemistry [On-line Journal] (47) 602-605.
CSU (1999 June 15, Updated). Physiologic Effects of Insulin. Colorado State University, Pathophysiology of the Endocrine System [On-line Biomedical Hypertextbook]. Available online through http://arbl.cvmbs.colostate.edu.
CSU (1999 June 15, Updated). Glucagon. Colorado State University, Pathophysiology of the Endocrine System [On-line Biomedical Hypertextbook]. Available online through http://arbl.cvmbs.colostate.edu.
Fish, S. Updated (2002 February 18, Updated). Insulin test. Medlineplus Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003700.htm.
CSU (1999 June 15, Updated). Insulin Synthesis and Secretion. Colorado State University, Pathophysiology of the Endocrine System [On-line Biomedical Hypertextbook]. Available online through http://arbl.cvmbs.colostate.edu.
Bruno Geloneze, Marcos A. Tambascia, José C. Pareja, Enrico M. Repetto and Luis A. Magna. The Insulin Tolerance Test in Morbidly Obese Patients Undergoing Bariatric Surgery. Obesity Research 9:763-769 (2001). Available online at http://www.obesityresearch.org/cgi/content/full/9/12/763 through http://www.obesityresearch.org.
Kolodziejczyk B, Duleba AJ, Spaczynski RZ, et al. Metformin Therapy Decreases Hyperandrogenism and Hyperinsulinemia in Women With Polycystic Ovary Syndrome. Fertil Steril. 2000 Jun;73(6):1149-1154.