Hemoglobin A1c is a test used to measure your average blood sugar levels over the past 3 months. It can be a useful tool for managing diabetes and can be used to make adjustments to your treatment plan and goals.

The hemoglobin A1c is a cornerstone blood test used in diabetes management since the 1990s. This test is taken at a physician’s office or diagnostic lab, either by fingerstick or blood draw from your vein. The A1C looks at your past 3 months or so of glucose levels, providing an average over that period of time to provide a more bird’s-eye view of how your diabetes management has been overall.

As diabetes technology and management tools advance, the reliance on A1C has become less of a focus than it once was when considered the only “gold standard” in diabetes care.

This article will answer some of the most common frequently asked questions (FAQs) relating to A1C and how it makes a difference in your diabetes management each day.

A1C is a simple blood test that measures your average blood glucose (blood sugar) levels as a percentage of hemoglobin over the previous quarter. You can think of it as sort of a summary of where your glucose levels have been during the last 3 months.

Once you’ve received a diagnosis of diabetes or prediabetes, the A1C is used to monitor your glucose management. Higher A1C readings are associated with a higher likelihood of developing diabetic complications.

As a summary of glucose levels over time, it presents a rough read on where a person’s glucose levels have been and an opportunity to make adjustments to diabetes care routines and set new goals.

You’re more than just a number

Managing diabetes includes actively measuring and monitoring glucose levels. It involves collecting a lot of numbers. But none of these numbers truly tells the whole diabetes story.

In the past, diabetes care focused primarily on A1C as a measure of “good” diabetes management. And sometimes having “good numbers” was equated with being “good” in your life with diabetes.

But this singular focus also created some negative impacts. People who couldn’t reach or keep up the ideal A1C level were often judged and stigmatized. They were labeled “bad” or “noncompliant” despite their best efforts.

As a result, some became too closely identified with their numbers. They felt good about themselves and their diabetes management only if they had “good” numbers. Faced with the impossible task of perfect glucose management, some became discouraged and lost motivation to actively manage their diabetes.

The American Diabetes Association (ADA)’s current Standards of Care call for individualized targets that take into account the person’s stage of life, health history, social determinants of health, and personal health goals.

This more modern approach recognizes and validates what people living with diabetes realized long ago: Our (glucose) numbers don’t tell the whole story when it comes to how well we’re managing our diabetes.

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A1C was recognized as an effective way to measure glycemic control as far back as the late 1960s. But it wasn’t until the late 1980s when the ADA began recognizing it, and then in the mid-1990s that the organization formally recommended adding A1C to a diabetes diagnosis.

The landmark Diabetes Control and Complications Trial (DCCT) published in 1993 followed a decade of research on the A1C, and it set the stage for this becoming the “gold standard” in diabetes care. DCCT demonstrated that a lower A1C generally means a lower risk of diabetes complications (eye, kidney, and nerves) developing.

Follow-up research known as the Epidemiology of Diabetes Interventions and Complications (EDIC) study confirmed those earlier results and showed the value of measuring glucose levels consistently over time.

Yes. The glucose levels measured during an A1C test are also important for people with type 2 diabetes. They can help see how glucose levels have been managed over the past 3 months and determine whether any diabetes care or medication changes are needed.

Generally, after you receive a diagnosis of diabetes, your A1C is checked twice a year. Sometimes, an A1C test every 3 months (or four times a year) might be prescribed if your glucose level goals aren’t being met or other health concerns arise. A1C tests can be done at any time of the day. They don’t require fasting.

The ADA’s Standards of Care 2022 and guidelines in recent years have shifted away from a one-size-fits-all target toward more individualized care. The current Standards of Care advise an A1C for most nonpregnant adults should be 7% or lower without significant hypoglycemia. Factors that might influence specific targets include:

  • whether the person is pregnant
  • the person’s age and life expectancy
  • how long ago the person received the diagnosis
  • comorbidities present
  • heart disease or vascular complications present
  • resources and support systems available to the person

The A1C goal of less than 7% is a starting point. Everyone should discuss their particular goal with their diabetes care team.

Since the A1C is based on an average over time, it’s difficult to see how it relates to glucose readings taken throughout the day. Scientists have come up with a calculation of estimated average glucose (eAG).

The eAG characterizes the mathematical relationship between a set of glucose readings (similar to the A1C) and “translates” it into a single number (similar to one glucose reading). For example, an A1C of 7% translates into an eAG of 154 mg/dL.

Even though it’s simply a calculation of the relationship, eAG can be one more tool used to track and manage your glucose levels. You can find an eAG calculator and table here.

The A1C is seen as generally accurate. But several factors can impact results.

  • Certain health conditions affect A1C results. These include:
  • Medications, including opioids and HIV medications, can affect A1C results.

It’s also important to remember that A1C doesn’t reflect fluctuations in your blood sugar or your glucose variability. That means you can see a lower or higher A1C result, but it doesn’t give you any insight as to whether your blood sugars drop to low or go high at different times of day.

Glucose levels from the past month (30 days) influence A1C results more than the levels from the previous 2 months. Because of this, dramatic and sustained changes in your most recent glucose levels will have an effect on A1C results. That means you can see an inaccurately higher or lower A1C based on those recent trends.

Don’t be surprised if there’s some difference between A1C results and the averages calculated from a fingerstick meter or continuous glucose monitor (CGM).

A1C is based on a single blood sample and reflects the impact of glucose levels over time. Those other averages are based on individual readings taken over time. With a CGM, the average can be labeled (in its app) as glucose management indicator (GMI). It’s still an average of glucose readings.

Time in range (TIR) calculates the percentage of time a person’s glucose readings are within their target range. This look goes beyond the average reported with A1C to show how much time the person’s glucose levels were either above or below their target range. The baseline target for well-managed glucose levels is to be in range at least 70% of the time.

This more nuanced view of glucose level management gives the person with diabetes and their healthcare team more information to base their care plans on.

Traditionally, A1C tests have required a blood draw taken in a clinic or lab. But newer tests that only require a fingerstick are more often available. These tests can be easily done in a doctor or healthcare professional’s office or at home. Both methods have been shown to be accurate and precise.

A1C remains a useful tool in managing diabetes overall. As CGM use becomes more common and more complete sets of glucose level data become available, A1C will move from being the dominant method for managing diabetes to one of a set of measures used for ongoing monitoring and goal setting in diabetes.