Every year, about 1.5 million Americans are diagnosed with diabetes, a condition characterized by chronically elevated blood sugar levels that can lead to serious complications over time. And far more than that (about 40% of Americans) have prediabetes — higher than normal blood sugar that hasn’t yet progressed to full-blown diabetes.
The good news: Many people with prediabetes (and even some with diabetes) can make healthy lifestyle changes that bring their levels back to normal — the key is knowing your blood sugar is elevated in the first place, and that’s where testing comes in.
Hemoglobin A1c (HbA1c, or sometimes just called an A1c) refers to the amount of glucose (or sugar) that’s attached to hemoglobin in the blood — and it’s a powerful biomarker to help identify prediabetes and diabetes, and to manage diabetes once someone is diagnosed.
Compared to other methods of measuring blood sugar — which offer more of an in-the-moment snapshot of blood sugar levels — an HbA1c test reveals your average blood sugar over several months, making it a more comprehensive assessment of potential blood sugar dysregulation.
What is an HbA1c test & how does it work?
An HbA1c test is a simple blood test that measures your average blood sugar over several months.
Hemoglobin is a protein in red blood cells that carries oxygen from your lungs to the rest of your body. When glucose builds up in the bloodstream, it binds to hemoglobin. An HbA1c test measures the percentage of hemoglobin proteins in your blood that are saturated with glucose. These saturated hemoglobin proteins are referred to as glycated hemoglobin.
Because red blood cells live an average of three months in the bloodstream, an HbA1c test is able to represent a pretty accurate three-month average of your blood sugar levels.
Acute stressors, recent exercise, and whether or not you’ve just eaten do not influence HbA1c results — so this test can be performed any time of day. However, your doctor may want to run HbA1c and a fasting glucose test simultaneously, which will require you to fast for approximately 8 hours in advance; and at-home test kits may require fasting as well.
Various health organizations — the American Diabetes Association (ADA), International Expert Committee (IEC), and the World Health Organization (WHO) — recommend using HbA1c to help diagnose diabetes. But it can also be a useful self-monitoring tool for people who want to be proactive about preventing prediabetes and diabetes altogether.
What’s a normal HbA1C level?
Your HbA1C test results 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 levels over the last several months, according to the ADA. Here are the thresholds used when diagnosing prediabetes or diabetes with an HbA1c test:
- Normal: HbA1c below 5.7% (although, some doctors believe optimal levels are between 4.0 and 5.3%; and that negative effects may begin as low as 5.5% in some individuals)
- Prediabetes: HbA1c between 5.7% and 6.4%
- Diabetes: HbA1c of 6.5% or higher
Wondering how exactly HbA1c percentages correspond with blood sugar? Here are the relative equivalents:
What does it mean if your HbA1c is high?
In simplest terms, high HbA1c means you have too much sugar in your bloodstream. If your HbA1c is between 5.7% and 6.4%, you may have prediabetes; if your HbA1c is 6.5% or higher, you may have diabetes. However, one test isn’t enough to deliver an official diagnosis. An HbA1c test should be repeated to confirm that results are consistent — or it can be used along with additional tests, such as a fasting blood glucose or an oral glucose tolerance test.
But an HbA1c can reveal more than just diabetes risk. Some research suggests numbers above 5.3% may be associated with an increased risk of Alzheimer’s disease and certain cancers. In some younger women, elevated HbA1c is also associated with polycystic ovarian syndrome (PCOS), a condition that can make it more difficult to conceive.
Symptoms of High HbA1c
Because HbA1c is a measure of long-term blood sugar, symptoms of high HbA1c — above 6.5% — are the same as symptoms of hyperglycemia or diabetes. Common signs that you may have elevated HbA1c and diabetes include the following:
- Increased thirst
- Frequent urination
- Blurred vision
Just keep in mind, if your HbA1c is in the prediabetes range (5.7%-6.4%) you may not experience any noticeable symptoms at all. So, if you have risk factors 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 HbA1c tests are used to monitor & manage diabetes
HbA1c tests are often used as a monitoring tool for people who already know they have diabetes. Typically, they’re repeated every 3-6 months. According to the ADA, the goal for most adults with diabetes is an HbA1c of less than 7% — the lower the better. The higher the number, the greater someone’s risk of developing serious diabetes complications such as cardiovascular disease, nerve damage, kidney damage, and memory problems.
Testing HbA1c regularly can help someone with diabetes determine when lifestyle changes are working and when they need to do more.
How quickly can you affect your HbA1c levels?
Because red blood cells live an average of three months (and HbA1c is a measure of the percentage of hemoglobin — red blood cell proteins — saturated with glucose), you could theoretically notice a decrease in your numbers within three months of adopting consistent healthy lifestyle changes. How much (and how quickly) you lower your HbA1c will depend on a variety of factors such as your specific diet and physical activity levels.
Keep in mind, though, reducing levels to this extent takes work!
Here are some proven ways to lower blood sugar that can help reduce HbA1c over time:
Scale way back on carbs and added sugars
Eliminating refined carbs and sugars (think: breads, cereals, pastas, sweets) is one of the best ways to curb blood sugar spikes. Even high-glycemic fruits, whole grains, and legumes should be consumed mindfully. Though these are certainly better than refined carbohydrates, they can still spike blood sugar for some people. Pairing these foods with a source of protein and fat can minimize the spike, and testing your blood sugar with a glucometer after meals can give you an idea of what specific carb sources you may tolerate better than others.
Move your body every day
Exercise contributes to healthier blood sugar and blood insulin levels. “When we exercise, especially moderately or vigorously, our body triggers our muscles to take up more glucose, removing it from the bloodstream,” says Dr. Brewer. And because there’s less circulating blood sugar to process, the pancreas doesn’t have to produce as much insulin.
Get consistent, high-quality sleep
Aim for around 7-9 hours of sleep every night and — just as importantly — go to bed and wake up at consistent times. Studies show that decreased sleep is a risk factor for high blood sugar. In fact, sleep deprivation over just one night increases insulin resistance, which can increase blood sugar.
Shortcomings of HbA1c tests
An HbA1c test isn’t a panacea for assessing metabolic health or glycemic control. For example, it’s possible to have a normal HbA1c even if you have elevated insulin — which isn’t good. Insulin is a hormone released by the pancreas in response to eating carbohydrates and sugars, and it helps usher sugar into cells where it can be used for energy. High insulin levels in the bloodstream mean that your body is working really hard to maintain normal blood sugar levels; and over time, this can progress to insulin resistance and diabetes. Several tests that can help identify insulin resistance are described in our guide to insulin resistance.
Additionally, anything that changes the lifespan of red blood cells — recent blood loss, sickle cell disease, transfusion, pregnancy, liver and kidney disease, iron deficiency anemia, and more — can impact HbA1c results, leading to falsely elevated or lowered results, according to the National Institute of Diabetes and Digestive and Kidney Diseases. For example, iron deficiency can give falsely high HbA1c results, while pregnancy can give falsely low HbA1c results.
Whether you have diabetes already or are just trying to take proactive steps to maintain 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 medical professional (such as a registered dietitian) to bring those levels down. Just keep in mind, an HbA1c test can’t do everything — so if you want a complete picture of your glycemic control and overall health, work with your doctor to determine additional testing that may be needed.