The A1C test measures a person’s average blood glucose or blood sugar levels over the past 3 months. An A1C reading of over 5.6% may be a cause for concern, but this will depend on various factors.

Doctors use the A1C test to check for prediabetes and diabetes. A range of 5.7–6.4% suggests a person may have prediabetes. Over 6.5% indicates diabetes.

This test also helps doctors monitor blood glucose levels in people with diagnosed diabetes.

Keeping A1C levels within the normal or target range lowers the risk of developing diabetes or its complications. Read on to learn what A1C test results mean.

A top-down view of several vials containing blood samplesShare on Pinterest
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The A1C chart below can help a person convert and understand their A1C test results. The doctor can provide more context and describe ways to keep blood glucose levels in a safe range.

A1C chart for diabetesShare on Pinterest
MNT-infographic_guide illustration by Diego Sabogal a1c-chart

The A1C test is also known as the:

  • hemoglobin A1C, or HbA1c, test
  • glycated hemoglobin test
  • glycohemoglobin test

The A1C test measures the percentage of red blood cells with glucose-coated hemoglobin. This measurement gives doctors an idea of the person’s average blood glucose levels over the past 2–3 months.

Hemoglobin is an iron-rich protein in red blood cells. It helps carry oxygen from the lungs to other tissues.

When glucose enters the blood, it binds to hemoglobin. The more glucose in a person’s bloodstream, the more hemoglobin is bound to glucose.

Undergoing the A1C test is straightforward: A healthcare professional takes a blood sample and sends it to a laboratory for testing.

A doctor may order this test to:

  • diagnose prediabetes
  • diagnose type 1 or type 2 diabetes
  • monitor the blood glucose levels of a person with diabetes to check how well their treatment is working

If a person takes insulin or other medications to manage diabetes, their doctor may also ask them to monitor their blood glucose levels at home. They can do this using a blood glucose meter or continuous glucose monitor. In this case, the person still needs to undergo regular A1C testing.

Traditionally, A1C levels come as a percentage. Alternatively, a doctor may report A1C results as estimated average glucose (eAG), milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).

Blood glucose meters and continuous glucose monitors also give eAG readings, some from at least 12 days of data.

The A1C test provides a more accurate long-term average. It considers fluctuations throughout the day, such as overnight and after meals.

A normal A1C level is below 5.7%. Normal eAG is below 117 mg/dL or 6.5 mmol/L.

If someone’s A1C levels are higher than normal, they may have diabetes or prediabetes. Their doctor might order a repeat test to confirm this.

Target levels in people with diabetes

A doctor will set a person’s target A1C level based on many factors. The right target varies from person to person.

For someone with diabetes, the target A1C level may depend on:

  • the person’s age
  • their overall health
  • whether they are pregnant
  • how long they have had diabetes
  • their prescribed treatment plan
  • any history of adverse effects from the treatment, including episodes of low blood glucose, or hypoglycemia
  • any complications from diabetes
  • the person’s preferences and treatment priorities

In general, a doctor might recommend aiming for A1C levels under 6.5% if a person:

  • is young and has a long life expectancy
  • has had diabetes for a short period
  • is effectively managing their diabetes with lifestyle changes or metformin alone
  • is otherwise in good health

A doctor might recommend A1C targets of 7.0–8.5% if a person:

  • is older and has a shorter life expectancy
  • has had diabetes for a longer period
  • has diabetes that is hard to manage, even with multiple medications
  • has a history of severe hypoglycemia or other adverse effects of treatment
  • has experienced complications of diabetes
  • has other chronic health conditions

People can work with their doctor to reassess and adjust their A1C targets over time. The condition and treatment goals may change.

Age is one of many factors that affect a person’s blood glucose levels. However, while advancing age is associated with increased blood glucose levels, the changes are often small.

Research from 2019 defined age-related A1C percentage levels in healthy populations as:

Age groupAll respondentsMenWomen
20–39 years4.0–6.04.1–6.14.0–5.8
40–59 years4.1–6.2 4.0–6.24.1–6.1
≥ 60 years4.4–6.64.4–6.64.4–6.5

To screen for diabetes, a doctor may order an A1C test for someone over 45 years. They may also do this for younger people who have other risk factors.

After diagnosing diabetes, a doctor determines how often to test A1C levels.

If a person meets their treatment goals, they may need an A1C test twice a year. When managing blood glucose levels is challenging, a person needs this test more frequently.

A person should make an appointment with their doctor if they:

  • have questions or concerns about their treatment plan
  • are finding it hard to keep their blood glucose levels within the target range
  • have had symptoms of high or low blood glucose levels
  • think they might have complications of diabetes

Symptoms of high blood glucose levels include:

  • fatigue
  • unusual thirst
  • frequent urination
  • blurred vision

Symptoms of low blood glucose levels include:

  • nervousness, irritability, or anxiety
  • confusion
  • dizziness
  • hunger
  • shaking
  • sweating

Anyone who develops any of the symptoms above or notices other changes in their health should inform a doctor.

A doctor orders an A1C test to check whether someone has prediabetes or type 1 or 2 diabetes. Doctors also use this test to monitor blood glucose levels in people with diabetes to check how well their treatment plan is working.

A1C test results are usually a percentage but may come as an eAG measurement. Target A1C levels vary from person to person, depending on age, overall health, and other factors.

Having high A1C levels may indicate a person has diabetes or a high risk of related complications. In this case, a doctor will work with the individual to adjust the treatment approach.