Hemoglobin A1c Test (HbA1c, A1c, Hb1c)

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: John P. Cunha, DO, FACOEP
    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.

Better Blood Sugar Balance

Hemoglobin A1c definition and facts

  • Hemoglobin A1c is a protein on the surface of red blood cells that sugar molecules stick to, usually for the life of the red blood cell (about three months).
  • The higher the level of glucose in the blood, the higher the level of hemoglobin A1c is detectable on red blood cells.
  • Hemoglobin A1c levels correlate with average levels of glucose in the blood over an approximately three-month time period.
  • Normal ranges for hemoglobin A1c in people without diabetes is about 4% to 5.9%. People with diabetes with poor glucose control have hemoglobin A1c levels above 7%.
  • Hemoglobin A1c levels are routinely used to determine blood sugar control over time in people with diabetes.
  • Decreasing hemoglobin A1c levels by 1% may decrease the risk of microvascular complications (for example, diabetic eye, nerve, or kidney disease) by 10%.
  • Hemoglobin A1c levels should be checked, according to the American Diabetic Association, every six months in individuals with stable blood sugar control, and every three months if the person is trying to establish stable blood sugar control.
  • Hemoglobin A1c has many other names such as glycohemoglobin, glycated hemoglobin, glycosylated hemoglobin, and HbA1c.

What is a hemoglobin A1c?

To explain what hemoglobin A1c is, think in simple terms. Sugar sticks to things, and when it has been stuck to something for a long time it's harder to the get sugar (glucose) off. In the body, sugar sticks too, particularly to proteins. The red blood cells that circulate in the body live for about three months before they die. When sugar (glucose) sticks to these red blood cells by binding to hemoglobin A1c, it gives us an idea of how much glucose has been around in the blood for the preceding three months. Hemoglobin A1c is a minor component of hemoglobin to which glucose binds. Hemoglobin A1c levels depend on blood glucose concentrations. The higher the sugar concentration in the blood, the higher the detectable hemoglobin A1c levels. At any point in time, hemoglobin A1c levels represent the average blood sugar concentrations in the person with diabetes for approximately the preceding 3 months.

What makes a person's hemoglobin A1c levels high or low?

Hemoglobin A1c levels can be altered by

  • oral or IV glucose intake,
  • fasting,
  • use of insulin, and
  • by combinations of these and other factors.

The goal for people with diabetes, with their doctor's help, is to establish stable blood glucose levels resulting in hemoglobin A1c levels that are at least below 7% to reduce or stop complications of diabetes (for example, diabetic nerve, eye, and kidney disease).

Complications of Uncontrolled Blood Sugar in Diabetes

In type 1 and type 2 diabetes, uncontrolled blood sugar can lead to a number of associated complications, for example:

  • Foot problems
  • Urological and sexual problems (urinary tract infections [UTIs], erectile dysfunction [ED]
  • Yeast infections
  • Heart disease
  • Kidney disease
  • Diabetic neuropathy
  • Diabetic eye disease

What are normal and elevated ranges for hemoglobin A1c?

  • In most labs, the normal range for hemoglobin A1c is 4% to 5.9%.
  • In well-controlled diabetic patients, hemoglobin A1c levels are less than 7.0%.
  • In poorly controlled diabetes, its level is 8.0% or above.

The benefits of measuring hemoglobin A1c is that is gives a more reasonable view of what's happening over the course of time (about 3 months) to the average glucose level in the blood. Hemoglobin A1c value does not bounce up or down as much as daily finger stick blood sugar measurements.

Hemoglobin A1c conversion chart (HbA1c chart)

While there are no guidelines to use hemoglobin A1c test levels as a screening tool, it gives a health-care professional a good idea that someone may be have diabetes if the value is elevated; however, it is used as a standard tool to determine blood sugar control in patients known to have diabetes.

The correlation between hemoglobin A1c levels and average blood sugar levels is presented in the following conversion chart:

A1c(%)Mean blood sugar (mg/dl)
6135
7170
8205
9240
10275
11310
12345

The American Diabetes Association currently recommends an A1c goal of less than 7.0%, while other groups such as the American Association of Clinical Endocrinologists recommend a goal of less than 6.5%.

Studies have shown there is a 10% decrease in relative risk for microvascular complications for every 1% reduction in hemoglobin A1c. So, if a person with diabetes has an initial hemoglobin A1c level of 10.7 and drops to 8.2, though they are not yet at goal (about 6.5%), they have managed to decrease their risk of microvascular complications by about 20%. The closer to normal the hemoglobin A1c, the lower the absolute risk for microvascular complications.

How often does a person with diabetes need to have their hemoglobin A1c levels checked?

The American Diabetes Association (ADA) suggests if people with diabetes want to reduce their hemoglobin A1c levels quickly, they should get their hemoglobin A1c levels checked every three months until they reach their treatment goals.

People with diabetes who are meeting treatment goals and have stable blood control are recommended to check their hemoglobin A1c every six months according to the ADA.

Tracking hemoglobin A1c levels allows an individual and their health-care professional to determine how well the person is controlling their blood sugar (glucose) levels over time. However, they are not a substitute for daily glucose monitoring.

REFERENCES:

American Diabetes Association. "Diagnosing Diabetes and Learning About Prediabetes." Updated: June 09, 2015.
<http://www.diabetes.org/diabetes-basics/diagnosis/>

McCulloch, D.K., MD. "Patient information: Preventing complications in diabetes mellitus (Beyond the Basics)." UpToDate. Updated: Jul 02, 2015.
<http://www.uptodate.com/contents/preventing-complications-in-diabetes-mellitus-beyond-the-basics>

National Diabetes Information Clearinghouse (NDIC). "The A1C Test and Diabetes."
<http://diabetes.niddk.nih.gov/dm/pubs/A1CTest/>

Last Editorial Review: 8/30/2016

Subscribe to MedicineNet's Diabetes Newsletter

By clicking Submit, I agree to the MedicineNet's Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet's subscriptions at any time.

Reviewed on 8/30/2016
References
REFERENCES:

American Diabetes Association. "Diagnosing Diabetes and Learning About Prediabetes." Updated: June 09, 2015.
<http://www.diabetes.org/diabetes-basics/diagnosis/>

McCulloch, D.K., MD. "Patient information: Preventing complications in diabetes mellitus (Beyond the Basics)." UpToDate. Updated: Jul 02, 2015.
<http://www.uptodate.com/contents/preventing-complications-in-diabetes-mellitus-beyond-the-basics>

National Diabetes Information Clearinghouse (NDIC). "The A1C Test and Diabetes."
<http://diabetes.niddk.nih.gov/dm/pubs/A1CTest/>

Health Solutions From Our Sponsors