Hemoglobin A1c (HbA1c): What to know if you have diabetes or prediabetes or are at risk for these conditions

Even if you don’t live with diabetes, you’ve likely heard certain terms related to the condition such as blood sugar, glucose, and insulin. Another important term that anyone with or at risk for diabetes should be familiar with is hemoglobin A1c (HbA1c).

What is hemoglobin A1c?

Hemoglobin is a protein in your red blood cells. Although its main job is carrying oxygen to tissues in your body, glucose (blood sugar) molecules can also attach to hemoglobin. Everyone has some amount of glucose attached to their hemoglobin.

“All of us, diabetic and nondiabetic alike, have blood sugar levels that fluctuate constantly,” says Dr. David M. Nathan, Editorial Advisory Board Member at Harvard Health Publishing, and founder of the Diabetes Center and director of the Clinical Research Center at Massachusetts General Hospital. But people with diabetes regularly have higher levels of blood sugar circulating in their bloodstream.

When someone with diabetes measures their blood sugar with an at-home blood sugar test, they get a snapshot of their blood sugar level at that moment in time. That number naturally goes up and down during the day as you eat, exercise, and sleep.

In contrast, the HbA1c test provides a measure of average blood sugar levels over a three-month period.

How is hemoglobin A1c measured?

Your doctor checks your HbA1c with a simple blood test. You may have a finger prick that specifically reads HbA1c levels, or you may have a vial of blood drawn through a needle in your arm. You can have the test at any time of day, and don’t need to fast beforehand.

With a finger stick, you get your results immediately. If your doctor is sending a vial of blood to a lab, you’ll get results within a day.

Testing HbA1c is standard for anyone at risk of diabetes or with diabetes. This allows you and your doctor to track your blood sugar trends over time to see if your average blood sugar levels are creeping up, and provides the opportunity to take steps to lower your blood sugar levels before you develop diabetes or if you have diabetes. Regular HbA1c tests can help you and your doctor determine if your current treatment is effective or needs adjustment.

How to convert HbA1c to average blood glucose in mg/dL

Since most day-to-day diabetes medication adjustments are made based on blood glucose (sugar) levels, it is useful to understand how HbA1c levels translate into average blood sugar levels. Blood sugar test results are measured in milligrams per deciliter, or mg/dL, while HbA1c values are reported as the percentage of hemoglobin that has glucose attached to it.

The conversion of HbA1c to average glucose levels is shown in the table below.

The conversion of HbA1c to average blood sugar levels allows those with diabetes to determine what blood sugar levels they should aim for on a day-to-day basis in order to achieve their target HbA1c levels.

What is a normal hemoglobin A1c range?

In general, a value below 5.7% means your blood sugar is in the normal range and you don’t have diabetes.

A value between 5.7% and 6.4% means you have prediabetes. This isn’t a one-way street to a diabetes diagnosis, but it should be a wake-up call, says Dr. Nathan. “Prediabetes is a warning sign that blood sugar levels are on the rise, and it’s time to think about losing some weight or maybe becoming more active before we check again in about two to three months,” he says.

Once you hit an A1c of 6.5%, you’re in the diabetes range.

Target A1c levels for people with diabetes

A high HbA1c value is the strongest risk factor for developing long-term complications from diabetes, says Dr. Nathan. “Especially eye disease that can result in blindness, kidney disease that can cause kidney failure, and nerve disease (neuropathy) that can lead to the need for amputation,” he says. "You don't need to panic, since it usually takes many years of high HbA1c or blood sugar levels to develop these complications. However, you shouldn't be complacent either. Controlling your blood sugar, blood pressure, and cholesterol levels over time are the best way to avoid the complications that affect people with diabetes."

If you have diabetes, your doctor will set a personalized A1c goal for you. The HbA1c goal for many people with diabetes is less than 7%. (Target A1c may be higher in older adults who may not be as vulnerable to these long-term complications, which take many years to develop.)

How to lower blood sugar levels if you have diabetes or prediabetes

To reduce your A1c, you and your doctor can develop a treatment plan involving changes to your diet, regular exercise, and, in many cases, medication.

Research shows one of the most effective ways to reduce blood sugar levels is by losing excess weight. Shedding 7% to 10% of your overall body weight makes your cells more responsive to insulin, the hormone that regulates blood sugar. Diet and exercise are key to weight loss.

Diet. The specific eating plan that works best for you depends on your lifestyle and personal preferences. The following guidelines support steady, healthy blood sugar levels:

• Eat smaller meals throughout the day.
• Fill most of your plate with non-starchy vegetables.
• Keep proteins lean or plant-based.
• Reduce or cut out added sugar.
• Choose healthy fats, such as olive oil.
• Reach for more whole foods and less processed fare.
• Drink plenty of water.

Exercise. No matter how you choose to move, make it a regular habit. Your goal should be at least 150 minutes a week of a heart-healthy activity such as a brisk walking or cycling.

If your blood sugar numbers still aren’t coming down, your doctor may prescribe one or more medications. Metformin (Glucophage) is usually the first-line diabetes treatment. Other options include DPP-4 inhibitors, GLP-1 agonists, SGLT2 inhibitors, sulfonylureas, and insulin, which may be added to metformin if blood sugar levels and HbA1c remain above your goal.