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A1c

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Also known as: Hemoglobin A1c; HbA1c; Glycohemoglobin; Glycated Hemoglobin; Glycosylated Hemoglobin
Formal name: A1c

At a Glance

Why Get Tested?

To monitor a person's diabetes and to aid in treatment decisions; to diagnose diabetes; to help identify those at an increased risk of developing diabetes

When to Get Tested?

When first diagnosed with diabetes and then 2 to 4 times per year; as part of a health checkup or when you have symptoms of diabetes

Sample Required?

A blood sample drawn from a vein in your arm or from a fingerstick

Test Preparation Needed?

None

The Test Sample

What is being tested?

The A1c test evaluates the average amount of glucose in the blood over the last 2 to 3 months. It does this by measuring the concentration of glycated (also often called glycosylated) hemoglobin A1c.

Hemoglobin is an oxygen-transporting protein found inside red blood cells (RBCs). There are several types of normal hemoglobin, but the predominant form – about 95-98% – is hemoglobin A. As glucose circulates in the blood, some of it spontaneously binds to hemoglobin A. The hemoglobin molecules with attached glucose are called glycated hemoglobin. The higher the concentration of glucose in the blood, the more glycated hemoglobin is formed. Once the glucose binds to the hemoglobin, it remains there for the life of the red blood cell – normally about 120 days. The predominant form of glycated hemoglobin is referred to as HbA1c or A1c. A1c is produced on a daily basis and slowly cleared from the blood as older RBCs die and younger RBCs (with non-glycated hemoglobin) take their place.

This test is used to monitor treatment in someone who has been diagnosed with diabetes. It helps to evaluate how well their glucose levels have been controlled by treatment over time. This test may be used to screen for and diagnose diabetes or risk of developing diabetes. In 2010, clinical practice guidelines from the American Diabetes Association (ADA) stated that A1c may be added to fasting plasma glucose (FPG) and oral glucose tolerance test (OGTT) as an option for diabetes screening and diagnosis.

For monitoring purposes, an A1c of less than 7% indicates good glucose control and a lower risk of diabetic complications for the majority of diabetics. However, in 2012, the ADA and the European Association for the Study of Diabetes (EASD) issued a position statement recommending that the management of glucose control in type 2 diabetes be more "patient-centered." Data from recent studies have shown that low blood sugar (hypoglycemia) can cause complications and that people with risk of severe hypoglycemia, underlying health conditions, complications, and a limited life expectancy do not necessarily benefit from having a stringent goal of less than 7% for their A1c. The statement recommends that people work closely with their doctor to select a goal that reflects each person's individual health status and that balances risks and benefits.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or a drop of blood is taken from a finger by pricking it with a small, pointed lancet.

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?

No test preparation is needed.

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

(Updated 2012 June 19). The A1C Test and Diabetes. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) [On-line information]. Available online at http://diabetes.niddk.nih.gov/dm/pubs/A1CTest/ through http://diabetes.niddk.nih.gov. Accessed October 2012.

Topiwala, S. (Updated 2012 April 29). HbA1c. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm. Accessed October 2012.

Horowitz, G. (Updated 2012 January 6). Hemoglobin A1c Testing. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2049478-overview#showall through http://emedicine.medscape.com. Accessed October 2012.

(© 1995-2012). A1C. American Diabetes Association [On-line information]. Available online at http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/ through http://www.diabetes.org. Accessed October 2012.

(© 1995-2012). Hemoglobin A1c, Blood. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/82080 through http://www.mayomedicallaboratories.com. Accessed October 2012.

(Updated 2011 November 4). For People of African, Mediterranean, or Southeast Asian Heritage: Important Information about Diabetes Blood Tests. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) [On-line information]. Available online at http://diabetes.niddk.nih.gov/dm/pubs/traitA1C/index.aspx through http://diabetes.niddk.nih.gov. Accessed October 2012.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 508-510.

Inzucchi, S. et. al. (2012 April 19 Online). Management of Hyperglycemia in Type 2 Diabetes: A Patient-Centered Approach, Position Statement of the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetes Care 2012;35:1364–1379. [On-line information]. PDF available for download at http://care.diabetesjournals.org/content/early/2012/04/19/dc12-0413.full.pdf through http://care.diabetesjournals.org. Accessed October 2012.

2010 Consensus Statement on the Worldwide Standardization of the Hemoglobin A1c Measurement. Ragnar Hanas and Garry John, on behalf of the International HbA1c Consensus Committee. Published May 27, 2010. Latest version available online at http://www.clinchem.org/cgi/doi/10.1373/clinchem.2010.150540 through http://www.clinchem.org. Accessed October 2012. 

 The Challenge of "Brittle" Diabetes. Johns Hopkins Health Alert. Available online at http://www.johnshopkinshealthalerts.com/alerts/diabetes/JohnsHopkinsDiabetesAlert_3541-1.html through http://www.johnshopkinshealthalerts.com. Accessed October 2012. 

(2013©) American Diabetes Association. Diabetes Basics, Diagnosing Diabetes and Prediabetes. Available online at http://www.diabetes.org/diabetes-basics/diagnosis/?loc=DropDownDB-diagnosis through http://www.diabetes.org. Accessed May 2012.

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.

(2002 May 01, Updated). Other Diabetes Management Tests, Glycosylated Hemoglobin. Diabetes Information, U.S Food and Drug Administration [On-line information]. Available online at http://www.fda.gov/diabetes/glucose.html#18 through http://www.fda.gov.

(1995-2004). Diabetes Mellitus. The Merck Manual of Medical Information-Second Home Edition [On-line information]. Available online at http://www.merck.com/mmhe/sec13/ch165/ch165a.html?qt=Diabetes&alt=sh through http://www.merck.com.

Mbanya, J. et. al. Working Group Members (2004 January 20). Report of the ADA/EASD/IDF Working Group of the HbA1c Assay. EASD All News [On-line Report]. Available online at http://www.easd.org/. (Click "All News" and "2004/05").

A.D.A.M., Updated (2003 October 10, Updated). HbA1c. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm.

(2004 June). 2004 NGSP Clinical Advisory Committee Meeting. American Diabetes Association 64th Annual Scientific Sessions, June 2004. NGSP, What's New [On-line information]. Available online at http://www.missouri.edu/~diabetes/ngsp/indexwn.html through http://www.missouri.edu.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 503-505.

Little, R., Nathan, D. and Sacks, D. (2008 December 9). Hemoglobin A1c: New Uses for Today and Possibilities for Tomorrow. AACC [Audioconference].

Holt, E. (2008 June 17, Updated). HbA1c. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm. Accessed on 12/13/08.

American Diabetes Association. A1C test. [On-line information]. Available online at http://www.diabetes.org/type-1-diabetes/a1c-test.jsp through http://www.diabetes.org. Accessed on 12/13/08.

(2008). But What Does My A1C Level Really Mean? American Diabetes Association [On-line information]. Available online at http://www.diabetes.org//diabetes-research/summaries/nathan-what-a1c-level-means.jsp through http://www.diabetes.org. Accessed on 12/13/08.

Nathan, D. et. al. (2008 June 7). Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care 31:1473-1478, 2008 DOI: 10.2337/dc08-0545 [On-line journal]. Available online at http://care.diabetesjournals.org/cgi/content/abstract/31/8/1473 through http://care.diabetesjournals.org. Accessed on 12/14/08.

Crandall, J. (2007 May, Revision). Diabetes Mellitus. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merck.com/mmpe/sec12/ch158/ch158b.html?qt=diabetes&alt=sh#sec12-ch158-ch158b-1159 through http://www.merck.com. Accessed on 12/14/08.

Consensus Committee (2007 September). Consensus Statement on the Worldwide Standardization of the Hemoglobin A1c Measurement. Diabetes Care v30 (9). [On-line journal]. PDF available for download at http://www.ifcc.org/4dc9925consensus.pdf through http://www.ifcc.org.

Kahn, R. and Fonseca, V. (2008 August). Translating the A1c Assay. DiabetesCare v 31(8) [On-line information]. PDF available for download at http://professional.diabetes.org/Content/Editorial.pdf through http://professional.diabetes.org. Accessed on 12/14/08.

(2007 November). Sickle Cell Trait and Other Hemoglobinopathies and Diabetes: Important Information for Physicians. National Diabetes Information Clearinghouse [On-line information]. Available online at http://diabetes.niddk.nih.gov/dm/pubs/hemovari-A1C/index.htm through http://diabetes.niddk.nih.gov. Accessed on 12/14/08.

S11 (2008). Q&A Estimated Average Glucose: an alternative to A1C. American Diabetes Association [On-line information]. Available online at http://professional.diabetes.org/GlucoseCalculator.aspx through http://professional.diabetes.org. Accessed on 12/21/08.

American Diabetes Association. Executive summary: standards of medical care in diabetes—2010. Jan 2010. Diabetes Care 33: S4-S10.

(January 2010) The Endocrine Society Statement on the use of A1c for Diabetes Diagnosis and Risk Estimation. PDF available for download at http://www.endo-society.org/advocacy/upload/TES-Statement-on-A1C-Use.pdf through http://www.endo-society.org. Accessed January 2010.

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