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Diabetes 101: What Is HbA1c And What Is A Normal Level?

Learn how HbA1c testing can help diagnose and manage diabetes and prediabetes.

Stephanie Eckelkamp

Medically reviewed by

Ford Brewer, M.D.


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Key takeaways
  • Hemoglobin A1c (HbA1c) is a measure of glucose, or sugar, in your blood. It’s an important tool for diagnosing diabetes and prediabetes.
  • An Hba1c test shows your average blood sugar levels at any time.
  • You can use HbA1c testing proactively if you’re concerned about developing diabetes.

Nearly half of all Americans have some form of diabetes, whether they know it or not. 

In a given year, more than 37 million diabetic Americans have already been diagnosed, 8.5 million remain undiagnosed, and another 96 million are living with prediabetes,¹² an earlier stage on the disease spectrum that is characterized by higher-than-normal blood sugar levels.

If left untreated, both prediabetes and diabetes can lead to serious health complications, including heart disease, Alzheimer’s, nerve and kidney damage, certain cancers and premature death. In some younger women, elevated HbA1c is also associated with polycystic ovarian syndrome (PCOS).³

Despite the high rates of diagnosis, there’s good news: if you have prediabetes, and possibly even if you have diabetes, you may be able to improve your blood sugar level with healthy lifestyle changes. But before you can reduce your blood sugar level, you’ll need to know what it is. This is where hemoglobin A1c (also known as HbA1c, or sometimes just A1c) testing comes in. 

If your healthcare provider suspects that you’re at risk for diabetes, they may suggest HbA1c testing, as it can help diagnose and manage both prediabetes and diabetes. 

What is an HbA1c test, and how does it work?

An HbA1c test is a simple blood test that measures your average blood glucose level over a period of time by looking at hemoglobin.

Hemoglobin is a protein found in red blood cells; its role is to carry oxygen from your lungs to the rest of your body. When glucose builds up in the bloodstream, it binds to hemoglobin and creates glycated (i.e., saturated with glucose) hemoglobin proteins. HbA1c testing measures the percentage of glycated hemoglobin proteins in your blood.

Here’s the extra-cool part: red blood cells live for about three months in the bloodstream, so an HbA1c test gives a three-month average of your blood sugar level. 

While there are other methods of measuring glucose that can show a snapshot of blood sugar, HbA1c provides a more comprehensive picture. There’s no specific prep required for an HbA1c test, but since it’s often combined with other types of tests, you might end up fasting before giving your blood sample.

There are several types of diabetes — type 1, type 2 and gestational diabetes (diabetes that happens during pregnancy) being the main ones. Of these, type 2 is the most common by far, affecting nine out of 10 Americans with diabetes. Additional tests (such as an oral glucose tolerance test) may be needed to confirm a diagnosis.

Various health organizations, like the American Diabetes Association (ADA), International Expert Committee (IEC) and the World Health Organization (WHO), recommend using HbA1c to help with the diagnosis of diabetes, but the test can also be used proactively. 

For people with an increased risk or family history of diabetes and for anyone who wants a baseline before making positive lifestyle changes, HbA1c testing is a useful self-monitoring tool that shows your body’s ability to handle glucose.

What's a normal HbA1C level?

Your HbA1C level can give you an idea of whether you have normal blood sugar, prediabetes or diabetes. Results are reported as a percentage — the higher the percentage, the higher your blood sugar over the last several months. 

Here are the HbA1c thresholds used for diagnosing diabetes and prediabetes:

  • Normal: Below 5.7%
  • Prediabetes: Between 5.7% and 6.5%
  • Diabetes: 6.5% or higher

What does it mean if your HbA1c is high?

In simple terms, a high HbA1c level means you have poor blood glucose control, in other words, too much sugar in your bloodstream. That said, one test isn't enough for an official diagnosis of diabetes or prediabetes — the test should be repeated to confirm that results are consistent. 

What are the symptoms of high HbA1c?

Symptoms of HbA1c levels above 6.5% are the same as symptoms of hyperglycemia or diabetes. Common signs associated with an increase in levels of HbA1c include:

  • Increased thirst
  • Frequent urination
  • Blurred vision
  • Fatigue

Just keep in mind that if your level of HbA1c is in the prediabetes range (5.7% to 6.4%), you may not experience any noticeable symptoms. So, if you are at risk for diabetes (obesity, high blood pressure, history of heart disease, lack of physical activity), it's particularly important to keep tabs on your HbA1c levels.

How are HbA1c tests used to monitor and manage diabetes?

HbA1c tests are often used by diabetic patients as a monitoring tool that can help with glycemic control. Typically, they're repeated every three to six months.

According to the American Diabetes Association, the target range for most people with diabetes is an HbA1c of less than 7%, but the lower, the better.¹⁰ Higher numbers mean an increased risk of diabetes complications.

Regularly testing HbA1c levels can help patients with diabetes determine if their lifestyle changes are working and if they need to adjust their treatment plan to reduce the risk of complications.

How quickly can you improve your HbA1c levels?

Because red blood cells live an average of three months, you could theoretically notice a decrease in your levels within three months of adopting consistent healthy lifestyle changes. How much (and how quickly) you lower your HbA1c will depend on various factors, like your diet and physical activity levels.

“I saw a patient with an HbA1c of more than 12, which is an extremely destructive number, get down to 8.5 in three months, and then to 6.5 in three more months...I've also seen plenty of people in the six-plus area get into the fives in three months," says Dr. Ford Brewer, a board-certified preventive and occupational medicine specialist. 

Keep in mind, though, that reducing levels to this extent takes work. 

"These drastic improvements require very significant lifestyle changes," says Dr. Brewer. "This typically means going from a typical standard American diet to a very low-carb or keto diet and adding in a new exercise routine."

Here are some proven ways to lower blood sugar and hit HbA1c targets over time:

  1. Scale back on carbs and added sugars.¹¹
  2. Eliminate refined carbs and sugars (think: breads, cereals, pasta, sweets). 
  3. Mindfully consume high-glycemic fruits, whole grains and legumes.¹² 
  4. Pair higher glycemic foods with a source of protein and fat to minimize blood sugar spikes.¹³
  5. Test your blood sugar with a glucometer after meals to understand what specific carb sources you may tolerate best.
  6. Aim for seven to nine hours of consistent, high-quality sleep a night.¹⁴¹⁵

What are the shortcomings of HbA1c testing? 

An HbA1c test isn't a total picture of metabolic health or glycemic control. For example, it's possible to have a normal HbA1c even if you have elevated insulin. Insulin, a hormone released by the pancreas in response to eating carbohydrates and sugars, helps usher sugar into cells where it can be used for energy. High insulin levels in the bloodstream mean your body is working extra hard to maintain normal blood sugar levels; over time, this can progress to insulin resistance —which is also linked to cardiovascular disease¹⁶ — and to diabetes. 

According to the National Institute of Diabetes and Digestive and Kidney Diseases, anything that changes the lifespan of red blood cells, including recent blood loss, sickle cell disease, blood transfusion, pregnancy, liver and kidney disease, iron deficiency and anemia, can affect HbA1c results and lead to falsely elevated or lowered results.¹⁷

In his practice, Dr. Brewer sees diabetic patients coming in with HbA1c values in the 5% range or even lower. 

“Their doctors tell them, ‘There's no way you have diabetes. You don't even have prediabetes,’” he says. “Then the patient shows the doctor their oral glucose tolerance test or insulin survey test, and their blood sugars, when challenged, are off the charts.” 

Dr. Brewer notes that these patients typically eat very low-carb diets, which explains their low HbA1c. So, while it’s great if your HbA1c is in the target range and you’re eating a diet that makes that range attainable, Dr. Brewer cautions that HbA1c should be considered the bare minimum of diabetes screening tests

If you’re concerned about your diabetes risk, Dr. Brewer suggests asking your doctor for the more comprehensive oral glucose tolerance test once a year or any time you gain 10 pounds or more. For this test, you’ll be given a strong glucose drink, then have your blood drawn at various intervals to measure your body’s response to the sugars. 


Whether you’re already diabetic or just trying to be proactive in maintaining optimal health and blood sugar, an HbA1c test is an extremely valuable tool. When you notice levels creeping up, it can be a great motivator to change your habits or start working with a healthcare professional to bring those levels down. Just remember that an HbA1c test is only one part of the picture, so if you want a complete assessment of your glycemic control and overall health, work with your doctor to determine if additional testing is needed.

Updated on
February 22, 2024
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  1. CDC. Prediabetes. Your Chance to Prevent Type 2 Diabetes. Accessed April 19, 2022. 
  2. Centers for Disease Control and Prevention. National Diabetes Statistics Report. Accessed April 19, 2022.
  3. Johns Hopkins Medicine. Polycystic Ovary Syndrome (PCOS). Accessed April 26, 2022. 
  4. American Diabetes Association. Understanding A1C: A1C and eAG. Accessed April 18, 2022.
  5. American Diabetes Association. Understanding A1C. Accessed April 18, 2022.
  6. CDC. Type 2 Diabetes. Accessed April 22, 2022. 
  7. American Diabetes Association. Understanding A1C. Accessed April 18, 2022.
  8. Centers for Disease Control and Prevention. Diabetes Symptoms. Accessed April 18, 2022.
  9. Centers for Disease Control and Prevention. Prediabetes – Your Chance to Prevent Type 2 Diabetes. Accessed April 18, 2022.
  10. American Diabetes Association. Understanding A1C. Accessed April 18, 2022.
  11. American Diabetes Association. Understanding Carbs. Accessed April 19, 2022. 
  12. Harvard T.H. Chan, School of Public Health. Carbohydrates and Blood Sugar. Accessed April 19, 2022. 
  13. National Library of Medicine. Protein: metabolism and effect on blood glucose levels. Accessed April 19, 2022.
  14. Centers for Disease Control and Prevention. Are You Getting Enough Sleep? Accessed April 19. 
  15. Journal of Applied Physiology. Sleep loss: a novel risk factor for insulin resistance and Type 2 diabetes. Accessed April 22, 2022.
  16. Cardiovascular Diabetology. Association between insulin resistance and the development of cardiovascular disease. Accessed April 22, 2022.
  17. National Institute of Diabetes and Digestive and Kidney Disease. The A1C Test & Diabetes. Accessed April 18, 2022.

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