The A1C test measures a person’s average blood sugar level over the previous 3 months. Doctors can use it to monitor diabetes and as a diagnostic tool for type 2 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 fingerprick test or through a wearable monitor.

A person can also visit a doctor’s office for an A1C test. This provides an average view of blood sugar levels over an extended period of time, usually 2–3 months. A1C testing is essential for most people with diabetes.

Read more to learn about how the test works, what it measures, and more.

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The A1C test is a blood test that measures the average glucose levels in the blood over the previous 3 months.

Doctors use the A1C test to determine how stable a person’s blood sugar levels are. They can also use it in the initial diagnosis of type 2 diabetes.

Other names for the A1C test include:

  • the hemoglobin A1C test
  • the glycated hemoglobin test
  • the glycohemoglobin test
  • the HbA1C test stands for

The HbA1C test stands for hemoglobin A1c. Hemoglobin is the protein in red blood cells that transports oxygen around the body.

Glucose attaches to hemoglobin to form glycated hemoglobin, which is also called hemoglobin A1C. When blood sugar levels are high, the body creates more glycated hemoglobin.

The A1C test measures these levels. Red blood cells live for around 120 days, or 4 months, and the A1C test measures the average blood glucose level over their lifespan.

A person can take the A1C test at any time. They do not need to fast before taking it or do any other preparation.

To perform the test, a doctor or other healthcare professional will draw blood either from a finger stick or a bvein in the arm. They then send it to a laboratory for testing.

Some doctors’ offices offer a point-of-care test, which means they analyze the blood themselves. While this may be useful for managing diabetes, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDKD) says that it is not suitable for diagnosis.

The A1C test is one of the tests doctors use to diagnose type 2 diabetes and prediabetes. They may also use other tests, such as a fasting blood glucose test or a 2-hour glucose tolerance test.

For adults over 45 years or for people with certain risk factors, doctors repeat the A1C test every 3 years.

If the A1C test shows someone has prediabetes, they can make lifestyle changes to lower their risk for type 2 diabetes. A doctor may advise repeating the A1C yearly or every 2 years.

Additionally, people living with diabetes typically have their A1C levels monitored regularly. This can help them manage their medications and health.

Learn more about preventing type 2 diabetes.

A1C test results show as a percentage. They refer 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. According to the NIDDK, if the A1C test shows 6.8%, the actual reading could be anywhere between 6.4–7.2%.

If the results show elevated A1C, a doctor may also check the person’s current blood sugar levels. If they are 200 milligrams per deciliter (mg/dl) or over, the doctor may diagnose diabetes.

A doctor will repeat these tests if A1C results, glucose scores, or both suggest a person has diabetes.

Additionally, a doctor may diagnose prediabetes if the results are 5.7–6.4%.

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 healthy diet, and taking regular exercise, can often reduce the risk.

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 diabetes monitoring. Regular A1C and glucose testing can show a doctor if a person’s treatment is working or needs adjustment.

Certain factors can cause inaccurate A1C results, including:

  • kidney problems
  • liver disease
  • severe anemia
  • blood loss or blood transfusions
  • early or late pregnancy
  • medications, such as opioids and some HIV medications
  • low iron levels
  • being unwell
  • stress

Furthermore, certain people may have a less common type of hemoglobin that can affect the test results. This includes individuals of African, Mediterranean, or Southeast Asian descent, as well as people with blood disorders such as sickle cell anemia or thalassemia.

If these factors apply, a doctor may suggest alternative or additional tests.

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

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 fingerprick test can reveal.

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

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

The ideal A1C level for a person can be a moving target. It can vary depending on a person’s age, medical conditions, and more.

A doctor can make recommendations based on these factors. They will also track changes in a person’s A1C levels over time.

Individuals living with diabetes have a customized treatment plan. An essential part of this plan involves a person self-monitoring their diabetes at home using a blood glucose meter or another device.

A person’s diabetes care team tells them how regularly and when they should test their blood sugar.

The self-monitoring device typically reports blood sugar levels in mg/dl. This measurement is a snapshot of blood glucose levels at the time of the test. Therefore, the levels vary depending on what a person eats, how much physical activity they do, and other factors, such as stress.

Self-monitoring helps people manage their diabetes and allows them to track whether they are meeting their A1C target.

It is important for people to manage blood sugar and A1C levels because experts associate increased levels with health complications, even if a person does not have diabetes. Elevated A1C levels are a significant risk factor for cardiovascular diseases and stroke in people who may have diabetes.

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

For example, in a large 2018 study, researchers found that the odds of developing type 2 diabetes increased fourfold for each percentage-unit increase in HbA1C.

Using A1C to prevent complications

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

Managing blood sugar 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% or lower can significantly reduce these risks.

However, everyone is different. An individual can work with a healthcare professional to determine their blood sugar and A1C targets.

A doctor may suggest an A1C test at the beginning of pregnancy. This can indicate whether or not someone with risk factors for diabetes has a high score.

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

If a person has gestational diabetes, a doctor may also test up to 12 weeks after delivery.

The ADA recommends regular A1C testing for people with diabetes.

For those without diabetes, the ADA recommends that anyone who is 45 years or more, or who is under 45 years but has risk factors for diabetes such as obesity, should seek a baseline test. An individual may need to attend further testing, depending on the result of their baseline test.

People who have had gestational diabetes during pregnancy may need to arrange a screening every 3 years.

The A1C test is useful for monitoring a person’s blood sugar levels if they have diabetes and diagnosing type 2 diabetes.

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

The A1C test measures the amount of hemoglobin in the blood with glucose attached. It provides a picture of average blood sugar levels over the previous 3 months and is a valuable tool for monitoring diabetes and diagnosing type 2 diabetes.

Doctors use the A1C test to check for prediabetes and diabetes in individuals over 45. They may also use the test for younger individuals if they are overweight or have other risk factors. People living with diabetes typically have A1C tests several times per year.

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