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The A1C test is a test for diabetes to measure a person's average blood glucose level over about 3 months. Doctors can use it to diagnose type 2 diabetes and to monitor people's diabetes.

In a blood glucose test, a person checks how much sugar — or glucose — is in their blood. They can do this at home with a finger prick test or a monitor that they can wear.

The A1C test provides an average view of blood sugar levels over an extended time, usually 2–3 months. A person will do an A1C test in the doctor's office.

A1C testing is essential for most people with diabetes. This article explains how this test works, and how it helps to manage blood sugar levels.

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Reaching target glucose levels can help a person reduce the risk of complications and maintain a good quality of life.

The A1C test is a blood test that measures the average glucose levels in the blood for 2–3 months.

Doctors use the A1C test to see how stable blood sugar levels are in a person with diabetes. Also, doctors can use it in the initial diagnosis of type 2 diabetes, but not type 1, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Other names for the A1C test are

  • the hemoglobin A1C test
  • the HbA1c test
  • the glycated hemoglobin test
  • the glycohemoglobin test

Hemoglobin is the protein in red blood cells that transports oxygen around the body. When blood glucose levels are high, some of the glucose binds to hemoglobin.

The type of hemoglobin that glucose attaches to is hemoglobin A. The name of the resulting combination is glycated hemoglobin (A1C).

Red blood cells live for around 120 days, or 4 months, and at the time of the test, there will be a direct link between the A1C result and the average blood glucose level over the previous 12 weeks or so.

A person can take the A1C test at any time. They do not need to fast before taking it or do any other kind of preparation. A doctor or other healthcare professional will take some blood and send it to the laboratory for assessment.

Some doctors' offices offer a point-of-care test, which means they analyze the blood themselves. This may be useful for managing diabetes, but the NIDDK note that it is not suitable for diagnosis.

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The A1C blood test measures blood glucose over approximately 3 months.

The result of the A1C test will be a percentage. This refers to the amount of hemoglobin that glucose has bound to in a person's blood.

For diagnosis, the test results may be as follows:

  • Normal: Below 5.7%
  • Prediabetes: 5.7–6.4%
  • Diabetes: 6.5% or more

One A1C test result does not mean that a person has diabetes. A doctor will also check the person's blood glucose levels. If the individual's blood glucose levels are 200 milligrams per deciliter (mg/dl), the doctor may confirm diabetes.

Various factors can change the result slightly, and some medical conditions can also lead to a higher A1C result.

According to the NIDDK, if the A1C test shows 6.8 percent, the actual reading could be anywhere between 6.4–7.2 percent.

Other conditions that can give a false A1C score for diabetes include:

  • kidney disease
  • liver disease
  • some blood disorders, such as sickle cell anemia
  • recent blood loss or transfusion
  • low iron levels
  • being unwell
  • stress

If a person has or may have any of these conditions the doctor can suggest another test or a different type of A1C test.

If A1C results, glucose scores, or both suggest that diabetes is present, but the person does not have symptoms, they may need to repeat the test.

A doctor may diagnose prediabetes if the results are between 5.7 and 6.4 percent.

A person with prediabetes has a higher chance of developing type 2 diabetes in the future, but lifestyle changes, such as quitting smoking, following a healthful diet, and getting regular exercise can often prevent this from happening.

The person may already have risk factors for type 2 diabetes, such as:

The A1C test is useful for diagnosis, but it is also important for monitoring. Regular A1C and glucose testing can show a doctor if a person's treatment is working well or if it needs some adjustment.

Average glucose, or eAG, is another way of reporting the results from an A1C test. It means the same, but some people prefer this way of interpreting the results because it uses the unit mg/dl, which is the same as the blood glucose test.

Here is a comparison between the two scores, based on a calculator from the American Diabetes Association (ADA) website.

A1C (%)eAG (mg/dL)
5.7117
6.4137
6.5140
7154
8183
9212
10240


The eAG score gives an idea of the average glucose levels in a person's blood over the previous 2–3 months, but it does not show the highs and lows that continuous glucose monitoring or the regular finger-prick test can reveal.

A person who does not have a diagnosis of diabetes should have a score for the A1C test of below 5.7 percent.

A person whose score is 6.5 percent or higher will have a diagnosis of diabetes, and they will need to begin treatment. This will involve lifestyle changes, such as dietary adaptations, additional exercise, and possibly medication.

During treatment for diabetes, the person will aim to keep their A1C score below 7 percent. However, different people will have different targets, depending on factors such as their age and the medications they use.

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People with a diagnosis of diabetes should have regular tests depending on what their doctor advises.

Managing blood sugar and A1C levels is necessary because a number of complications can develop with diabetes, such as cardiovascular disease.

As A1C percentages rise, so does the risk of prediabetes becoming type 2 diabetes, and complications arising in those who already have a diagnosis.

For example, one research team found that people with an A1C of 6.0–6.5 percent frequently had a 20-times higher risk of developing diabetes within 5 years when investigators compared them with people who had an A1C score of less than 5 percent.

The 2010 review looked at 16 studies that included more than 44,000 people who researchers had studied over 5.6 years.

Using A1C to prevent complications

People with diabetes need to manage their blood sugar levels to prevent these becoming too high.

Managing glucose levels can reduce the risk of complications affecting the small blood vessels, especially of the eyes and kidneys, and the coronary arteries.

This can help to prevent the many problems that can occur with diabetes, including:

  • vision loss
  • cardiovascular disease
  • stroke
  • kidney disease

Reaching and maintaining an A1C of 7 percent or lower can significantly reduce these risks.

However, an individual will work out their own blood sugar and A1C targets with their doctor or another healthcare provider, as each person is different.

A doctor may suggest the A1C test at the beginning of a pregnancy, to see if someone with risk factors for diabetes has a high score.

Later in the pregnancy, they may test for gestational diabetes in other ways as pregnancy can affect the A1C test result.

If a person has gestational diabetes, the doctor may also test up to 12 weeks after delivery, as gestational diabetes can sometimes develop into type 2 diabetes afterward.

The A1C test is useful for diagnosing type 2 diabetes and for monitoring a person's blood glucose levels if they have the condition.

It is also sensible to do regular blood glucose tests at home and to follow the correct treatment plan for diabetes between tests.

Glucose testing kits are available for purchase online.