What is a hemoglobin A1c measurement?

If you have diabetes, your doctor should measure your A1C level a minimum of two times a year. (If you change diabetes treatment, or if you are not meeting your blood glucose goals, you and your doctor will want to check your A1C level more often, about every three months).

The HbA1c (hemoglobin A1C) test measures how much glucose has become attached to a protein called hemoglobin in your red blood cells. Because the glucose sticks to the hemoglobin for several months, it provides a long-term picture of your blood glucose control.

Ideally, your results should be below 7%.
The hemoglobin A1C (HbA1C) test is a way to get an average of how well blood glucose (sugar) has been controlled for the past three months. The test measures the percentage of hemoglobin (red blood cells) that has been glycated, or "hooked up," with glucose. The normal role of hemoglobin in red blood cells is to carry oxygen throughout the body. But when blood glucose levels increase, some of that glucose ends up sticking to hemoglobin. Since a red blood cell lasts about 120 days, the A1C test can show an average for the last three months.
William Lee Dubois
Endocrinology Diabetes & Metabolism
The HbA1c, often just called an A1C (aye-one-see), is a blood test that can give us an idea of your body’s average blood sugar over the last couple of months. Sometimes the test is sent to a lab along with other routine blood tests, and other times it may be done at the doctor’s office using a fingerstick sample.
The purpose of the test is to get some idea of how well controlled your diabetes is, and to make sure your blood sugars are not at dangerous levels.
Here’s how it works: red blood cells are like the FedEx trucks of your body. They shuttle packages of oxygen and carbon-dioxide around from your lungs to your cells and back again. Your blood stream is the highway these “trucks” drive on. Now let’s pretend that it’s winter. If the roads are muddy and icky, the trucks are going to get dirty.
In your body, sugar molecules stick to the skins of red blood cells just like the dirty slush of winter roads stick to the white trucks, making them dirty.
The percentage of the skin of the blood cells covered in sugar give us the A1C score. For most diabetics a score between 6.0 and 6.9 is considered in good control. For perspective, kidney damage can start at scores over 9.0 while non-diabetics are typically under 5.0 percent.
Now, you might wonder why you need this test if you are checking your blood sugar with a meter at home, and the simple answer is that it is a great way to double check that the meter is working right and that you aren’t missing something. For instance, let’s just say you check your blood sugar first thing in the morning and at bed time, and things look great. Your numbers are always where you want them. But what if you spent all day high? Well, then our A1C score would come back higher than expected, and we could investigate why the A1C and the meter don’t agree, and could then adjust your therapy.
The A1C score is not perfect, if you ran really high half the time and really low half the time, you could have a score that looked deceptively good. But it is still an important tool both to look at how good your diabetes control is, and if it is changing for the better or worse.
The test is usually run every three months for the simple reason that red blood cells live for three months, so any sample will reflect the sugar environment in your blood over the last three months.
Phil Southerland
A1c is a commonly used three-month average measure of your blood sugar. The government’s National Diabetes Education Program calls A1c “the best test for you and your health care team to know how well your treatment plan is working over time.”
Not Dead Yet: My Race Against Disease: From Diagnosis to Dominance

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Not Dead Yet: My Race Against Disease: From Diagnosis to Dominance

Part memoir, part sports adventure, Not Dead Yet tells the inspirational story of Phil Southerland’s battle with Type 1 diabetes and how from diagnosis to sheer determination, Phil Southerland beat...
Jonathan A. Fialkow, MD
Cardiology (Cardiovascular Disease)
The hemoglobin A1C (HbA1c) test is a measure of glucose coating red blood cells, which can also be used to identify abnormal blood sugar. It provides an indication of the average blood sugar level over the previous three months.
  • A normal A1C is less than 5.7.
  • Readings ranging from 5.7 to 6.4 are consistent with prediabetes, indicating an elevated risk for developing type 2 diabetes.
  • Two readings of 6.5 and above are consistent with a diagnosis of diabetes.
It’s not just about how many calories you take in, but how different people handle different kinds of calories. For example, some people can metabolize sugar better than others.
Lauren E. Frost, MD
Cardiology (Cardiovascular Disease)
The hemoglobin A1C is a measure of glucose that coats red blood cells, and it can be used to identify abnormal blood sugar that may lead to diabetes. It provides an indication of a person’s average blood sugar level over the previous three months.
  • A normal A1C is less than 5.7.
  • Readings ranging from 5.7 to 6.4 indicate prediabetes, which means a person has a higher risk for developing type 2 diabetes.
  • Two readings of 6.5 and above may indicate a diagnosis of diabetes.         
Unlike other tests to diagnose diabetes, which measure blood sugar levels at a specific time, a hemoglobin A1c (HbA1c) test measures your average blood sugar level over the past 3 months. A1c measurements are also used to monitor diabetes management. There are no special preparations for this blood test.

What your results mean:

- 3.0 percent -- 6.0 percent: Normal
- 6.1 percent -- 6.4 percent: High risk (the A1c test is not routinely used to diagnose prediabetes)
- 6.5 percent+: Diabetes
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Marjorie Nolan Cohn
Nutrition & Dietetics

A1C test is used to diagnose diabetes. An A1C level of 6.5 percent or higher on two separate tests indicates you have diabetes. A result between 5.7 and 6.4 percent is considered prediabetes, which indicates a high risk of developing diabetes.

For someone who doesn't have diabetes, a normal A1C level can range from 4.5 to 6 percent. Someone who's had uncontrolled diabetes for a long time might have an A1C level above 9 percent.

For most people who have previously diagnosed diabetes, an A1C level of 7 percent or less is a common treatment target. Higher targets may be chosen in some individuals. If your A1C level is above your target, your doctor may recommend a change in your diabetes treatment plan. Remember, the higher your A1C level, the higher your risk of diabetes complications.

Continue Learning about Lab Tests

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.