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Insulin

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Also known as: Fasting Insulin
Formal name: Insulin, serum
Related tests: C-peptide, Glucose Tests

At a Glance

Why Get Tested?

To help evaluate insulin production by the beta cells in the pancreas; to help diagnose the presence of an insulin-producing tumor in the islet cells of the pancreas (insulinoma); to help determine the cause of low blood glucose (hypoglycemia); to help identify insulin resistance, or to help determine when a type 2 diabetic might need to start taking insulin to supplement oral medications

When to Get Tested?

When you have low blood glucose levels with symptoms such as sweating, palpitations, dizziness, fainting; when you have diabetes and your health practitioner wants to monitor your insulin production; sometimes when it is suspected that you have insulin resistance

Sample Required?

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, but occasionally a health practitioner may do the test with, for example, a glucose tolerance test. In some cases, a health practitioner may request that you fast longer.

The Test Sample

What is being tested?

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, the body's main source of energy. Insulin helps transport glucose from the blood to within cells, helps regulate blood glucose levels, and has a role in lipid metabolism. This test measures the amount of insulin in the blood.

Insulin and glucose blood levels must be in balance. After a meal, carbohydrates usually are broken down into glucose and other simple sugars. This causes the blood glucose level to rise and stimulates the pancreas to release insulin into the blood. As glucose moves into cells, the level in the blood decreases and release of insulin by the pancreas decreases.

If an individual is not able to produce enough insulin, or if the body's cells are resistant to its effects (insulin resistance), glucose cannot reach most of the body's cells and the cells starve, while blood glucose rises to an unhealthy level. This can cause disturbances in normal metabolic processes that result in various disorders and complications, including kidney disease, cardiovascular disease, and vision and neurological problems.

Diabetes, a disorder associated with high glucose levels and decreased insulin effects, can be 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.

With insulin resistance, the body is unable to respond to the effects of insulin. The body compensates by producing additional amounts of the hormone. This results in a high level of insulin in the blood (hyperinsulinemia) and over-stimulation of some tissues that have remained insulin-sensitive. Over time, this process causes an imbalance in the relationship between glucose and insulin and, without treatment, may eventually cause health complications affecting various parts of the body.

In addition to type 2 diabetes, insulin resistance may be seen in those with polycystic ovarian syndrome (PCOS), prediabetes or heart disease, metabolic syndrome, and with disorders related to the pituitary or adrenal glands.

Other than in insulin resistance, hyperinsulinemia is most often seen in people with tumor of the islet cells in the pancreas (insulinomas) or with an excess amount of administered (exogenous) 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 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, a person will be asked to fast for 8 hours before blood is collected, but occasionally a health practitioner may do testing when fasting is not possible, such as when a glucose tolerance test (see Glucose) is done. In some cases, the health practitioner may request that a person fast longer than 8 hours.

The Test

Common Questions

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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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(© 1995–2013). Insulin, Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8664 through http://www.mayomedicallaboratories.com. Accessed December 2013.

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(Reviewed 2013 June 7). Insulin Basics. American Diabetes Association [On-line information]. Available online at http://www.diabetes.org/living-with-diabetes/treatment-and-care/medication/insulin/insulin-basics.html through http://www.diabetes.org. Accessed December 2013.

Delgado, J. et. al. (Updated 2013 January). Hyperinsulinemic Hypoglycemia. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/HyperinsulinemicHypoglycemia.html?client_ID=LTD#tabs=0 through http://www.arupconsult.com. Accessed December 2013.

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Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pg 345.

McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 211-212.

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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.

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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.

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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.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 567-568.

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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.

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