Hemoglobin A1c Test

Medically Reviewed on 4/1/2022

Things to know about hemoglobin A1c test

Hemoglobin A1c Levels and Ranges
Hemoglobin A1c Levels and Ranges

Hemoglobin is the molecule within red blood cells that carries oxygen to the body’s tissues. A small percentage of the hemoglobin has sugar attached to it, and this type of hemoglobin is known as hemoglobin A1c. The amount of hemoglobin A1c depends on the level of sugar (glucose) in the blood: the higher the blood sugar the higher is the amount of hemoglobin A1c.

  • 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.
  • Normal ranges for hemoglobin A1c in people without diabetes are 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, the 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 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 get the 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 the doctor 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. Other ways hemoglobin A1c may be termed include HbA1c, A1c, and Hb1c.


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What causes high or low hemoglobin A1c levels?

Hemoglobin A1c levels can be altered by:

  • Oral or IV glucose intake
  • Fasting
  • Use of insulin
  • 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).

What are normal hemoglobin A1c levels, and are low or high levels dangerous?

In a healthy person, the A1c level is less than 6% of the total hemoglobin. It is recommended that treatment of diabetes be directed at keeping an individual A1c level as close to the normal range (<6%).

  • 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 benefit of measuring hemoglobin A1c is that it 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 values do not bounce up or down as much as daily finger stick blood sugar measurements.

Chart of Normal and Elevated HbA1c Levels
Diagnosis* A1C Level
*Any test for diagnosis of diabetes requires confirmation with a second measurement unless there are clear symptoms of diabetes.

SOURCE: Centers for Disease Control and Prevention
Normal Below 5.7 %
Prediabetes 5.7% to 6.4%
Diabetes 6.5% or greater

Hemoglobin A1c conversion chart (HbA1c chart)

While there are no guidelines to use hemoglobin A1c test levels as a screening tool, it gives a healthcare professional a good idea that someone may 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:

Hemoglobin A1c Levels and Average Blood Sugar Levels Equivalent Chart
A1c (%) Mean blood sugar (mg/dl)
6 135
7 170
8 205
9 240
10 275
11 310
12 345

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%. In 2016, the ADA recommended an A1c level of 6.5% as a cutoff level to diagnose diabetes.

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 should you check your hemoglobin A1c levels?

The American Diabetes Association (ADA) suggests that 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 healthcare 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.

Medically Reviewed on 4/1/2022
American Diabetes Association. "Diagnosing Diabetes and Learning About Prediabetes." Updated: Nov 21, 2016.

McCulloch, DK, MD, et al. " Patient education: Preventing complications in diabetes mellitus (Beyond the Basics)." UpToDate. Updated: Feb 05, 2018.

National Diabetes Educational Initiative. Diabetes Management Guidelines 2016. Updated: Jan 2016.

NIH. The A1C Test and Diabetes. NIH. Updated: April 2018.