An A1C of 6.5% or higher indicates diabetes. Dangerous levels of A1C are 9% and higher. An A1C above 9% increases the risk of long-term diabetes complications like blindness, nerve damage, and kidney failure. Under 7% is considered good diabetes control.

In non-diabetics, A1C levels stay below 5.7%. An A1C between 5.7% and 6.5% suggests prediabetes.

This article explains what happens to your body when your A1C is too high. It also details what different A1C levels mean and complications from dangerously high A1Cs. More importantly, it shows how monitoring your A1C levels can help to prevent diabetic complications.

How A1C Measures Blood Sugar

An A1c test is also known as glycated hemoglobin, glycohemoglobin, or HbA1c. It measures the amount of glucose in your blood. More specifically, it checks hemoglobin, an iron-rich protein that transports oxygen and nutrients throughout the body.

Glucose (a sugar the body uses for energy) binds to hemoglobin, creating glycated hemoglobin compounds. The higher your blood glucose level, the more glucose attaches to the hemoglobin. Hemoglobin cells last about 90 days, so the A1C provides an overall picture of your blood sugar control for the previous three months.

For people without diabetes, A1C tests are recommended every three years in adults over the age of 45 and anyone with a high risk of diabetes. Risk factors include a family history of diabetes, a BMI above 25, high blood pressure, a history of heart disease, and a lack of physical activity.

For people with diabetes, regular A1C monitoring can catch a spike in blood sugar levels early. An increase should prompt your healthcare provider to re-evaluate your treatment plan. This may include a review of your medications, diet, and how often your test your blood sugar.

What Is a High A1C?

A1C results show the percent of glucose and hemoglobin bound together in your bloodstream. For example, a 5% A1C indicates five out of every 100 hemoglobins are glycated. The higher your A1C, the greater the risk of developing complications.

The A1C ranges for normal, prediabetes, and diabetes are:

Normal: Less than 5. 7%Prediabetes: 5. 7% to 6. 4%Diabetes: 6. 5% or higher

Talk to your healthcare provider if your A1C is in the prediabetic range. Prediabetes is a risk factor for type 2 diabetes. A diet change, increased activity, and moderate weight loss can help improve blood sugar control to prevent diabetes.

A1C Levels in People with Diabetes

For people with diabetes, an A1C under 7% is typically considered good control. Research shows an A1C above 9% significantly increases the risk of diabetic complications. For adults with diabetes, the target A1C range is typically between 7% and 8%. This depends on your age and other health factors.

A1C levels correspond to the following average blood sugar levels: 

Complications of High A1C Levels

Studies show high A1C levels increase the risk of severe diabetes complications. Blood vessel damage can start at A1C levels above 7%. The risk of complications significantly increases at A1Cs above 9%.

Heart Disease and Stroke

People with diabetes are at an increased risk of heart disease. Chronic high blood sugar levels can damage nerves and blood vessels that control the heart.

Diabetics also tend to develop heart disease younger than those without diabetes. The longer you have diabetes, the more likely it is you also have heart disease.

Coronary artery disease is the most common type of heart disease. It is caused by the buildup of plaque in the walls of the coronary arteries—the blood vessels that supply blood and oxygen to the heart.

Plaque—cholesterol, fat, and cellular waste—builds up in a process known as atherosclerosis. This decreases blood flow to the heart, which can cause a heart attack.

Decreased blood flow to the brain can also cause a stroke. Diabetes is linked to an increased risk of stroke and higher rates of mortality from stroke.

Diabetes also increases your risk of other heart disease risk factors. These include:

High blood pressure High LDL cholesterol High triglycerides

In addition, diabetes increases the risk of heart failure, which means your heart can’t pump blood very well. 

Blindness

High blood sugar can cause eye damage, leading to poor vision and vision loss. Common diabetic eye diseases include:

diabetic retinopathy diabetic macular edema (fluid retention in the retina) cataracts glaucoma

Diabetic eye diseases can largely be prevented by managing your blood sugar levels. Over time, high blood glucose levels damage the tiny blood vessels in the back of your eyes.

Damaged blood vessels may leak fluid and cause swelling. New blood vessels that form may be weak. These blood vessels can bleed into the middle part of the eye, cause scarring, or dangerously increase pressure inside your eye.

Diabetic eye changes are often without symptoms at first. Eye damage can begin during the prediabetes stage and typically progresses slowly.

A full, dilated eye exam helps find and treat eye problems early—before much vision loss can occur.

Adults with type 1 diabetes should get a dilated eye exam within five years of diagnosis and every year after that.

Adults with type 2 diabetes should get an eye exam soon after diagnosis and a dilated eye exam every year after. If you maintain good glucose control, you may only need a diabetic eye exam every other year.

Nerve Damage

Nerve damage caused by diabetes is called diabetic neuropathy. High blood sugar damages your nerves, which stop sending messages to different parts of your body.

Nerve damage can cause problems ranging from mild numbness to severe pain. Half of all people with diabetes have nerve damage. 

Common types of neuropathy in people with diabetes include:

Peripheral nerve damage: This affects hands, feet, legs, and arms. The most common type of diabetic nerve damage. Generally starts in both feet at once. Autonomic nerve damage: This affects the heart, bladder, stomach, intestines, sex organs, or eyes. Proximal nerve damage: This affects nerves in the thighs, hips, buttocks, legs, abdomen, and chest. Focal nerve damage: This affects single nerves, most often in your hand, head, torso, or leg.  

Symptoms of nerve damage include:

Burning painMuscle crampsNumbnessPoor balanceProblems with coordinationSharp, shooting painsTingling or pins and needlesUrinary or bowel incontinence

Maintaining a lower A1C is the best way to prevent or delay diabetic nerve damage.

Kidney Disease

High A1C levels increase the risk of diabetic kidney disease. One in three adults with diabetes has diabetic nephropathy (kidney disease).

Like with the eyes, heart, and nerves, high blood glucose damages blood vessels in the kidneys. When that happens, the kidneys are less able to filter out waste products and extra fluid.

Diabetic nephropathy typically does not have any early symptoms. As the condition worsens, it can cause: 

Confusion and difficulty concentratingFatigueHigh blood pressureLoss of appetiteMore frequent urination Nausea and vomitingPersistent itchingProtein in the urineShortness of breathSwollen feet, ankles, hands, or eyes

Many people with diabetes also develop high blood pressure, which can also damage the kidneys.

Gum Disease

High blood glucose also increases the sugar content in your saliva. This exposes the mouth, teeth, and gums to more sugar, germs, and plaque. This can irritate gums, causing gum disease.

In addition to gum disease, your jaw, tongue, and other mouth tissue can be affected. The most common gum disease and other mouth problems that people with diabetes have include:

Gingivitis (unhealthy or inflamed gums) Oral burning Periodontitis Thrush (oral yeast infection) Xerostomia (dry mouth)

Some of the first signs of gum disease are swollen, tender, or bleeding gums. You may not have any overt signs of gum disease until serious damage has occurred. The best defense is to brush your teeth twice a day and visit your dentist twice a year.

How to Lower High A1C Levels

Managing blood sugar to keep your A1C in your target range can prevent diabetic complications. If your A1C is high, work with your healthcare team to develop a plan. Blood-sugar lowering strategies primarily include self-management tools and making healthy choices.

At-Home Blood Sugar Monitoring

A1C is an important tool for managing diabetes but doesn’t replace at-home blood sugar monitoring. Research shows a direct link between more frequent blood sugar testing and a lower A1C.

At-home monitoring can be done with either a glucometer or a continuous glucose monitoring system (CGMS).

A glucometer (blood sugar meter) uses test strips and a tiny sample of blood from your finger. It shows your approximate blood sugar at the time of testing. CGMS uses a tiny sensor under the skin that continuously checks your blood sugar. It transmits readings over Bluetooth to your smartphone or other devices. Research shows using CGMS can help significantly reduce A1C.

Talk to your healthcare provider about how often you should test your blood sugar. In addition, keeping a blood sugar log can provide valuable information to you and your health team. This can help determine what (if any) changes to make to your treatment plan.

Healthy Eating and Meal Tracking

Diet has a huge impact on your blood sugar. In particular, carbohydrates like bread, rice, potatoes, and sweets raise your blood sugar. During digestion, the body breaks carbohydrates down into glucose.

One way to find out how certain foods affect your blood sugar is to test two hours after eating. Keeping a food journal along with blood sugar logs helps identify high blood sugar patterns. This can help you learn to manage your glucose levels better and lower your A1C.

Talk to your healthcare team if you are unsure what you should eat to manage your blood sugar. A dietitian or certified diabetes educator can help you learn how to balance meals for lower blood sugar.

Stress Relief Techniques

Managing stress is crucial to staying healthy in general and can particularly help people with diabetes.

Studies have shown that acute stress raises blood sugar levels by spurring glucose production and hindering insulin sensitivity. Better control of stress can positively impact blood sugar levels.

Some stress relief techniques include:

YogaJournalingMeditatingTalk therapy

Stay Active

Exercise helps to lower glucose levels by improving insulin sensitivity. Insulin is a hormone that helps glucose from the blood enter your muscles and organs. Research shows moderate exercise improves insulin sensitivity for up to 24 hours.

When you exercise, your muscles use glucose for energy. This lowers glucose levels in the blood. Studies show long-term regular physical activity has a positive impact on A1C levels. Exercise also helps to spur weight loss, reduce stress, and improve cardiovascular health.

The more exercise, the greater A1C reduction. Most people with diabetes should aim for at least 150 minutes of moderate-intensity exercise each week.

Medication

If you cannot lower your A1C through lifestyle changes, medication may be warranted.

Type 1 diabetics require insulin. Your endocrinologist may make adjustments to your basal and bolus rates. Bring up-to-date glucose logs and food journals to your appointment. This data can help your doctor or diabetes nurse dial in the right insulin-to-carb ratio and basal rates. If that doesn’t bring your A1C down, other medications can be added to help improve control.

Prescription medication for type 2 diabetes work in a few different ways. Some help your body make more insulin, and others help your body use the insulin it makes. Some people with type 2 diabetes use insulin to manage their blood sugar.

Remember to take your medication as prescribed and check with your healthcare team if you have any questions.

Summary

The A1C test measures the average blood glucose level over a three-month span. It is used to diagnose diabetes and monitor diabetic treatment.

A high A1C level increases your risk of diabetic complications. Over time, high blood sugars cause cardiac disease, diabetic retinopathy, kidney failure, neuropathy, and gum disease.

For people with diabetes, getting regular bloodwork can catch a high A1C early. At-home blood glucose monitoring, a low-carbohydrate diet, and exercise can help lower your A1C. If lifestyle changes do not help, your doctor may prescribe medications or change your doses. Talk to your healthcare team about any issues or questions you have.

A Word From Verywell

A high A1C is a sign that your diabetes care plan isn’t working. Blood sugar management depends primarily on self-care: counting carbs, testing your blood sugar, and making healthy choices. Burnout is common and nothing to be ashamed of. The important thing is to get back on track.

If you are struggling with diabetes self-management, talk to your healthcare team. Be honest about your challenges so they can help you set healthy goals. Resources like a certified diabetes educator, dietitian, or the online diabetes community can be a big help. Living with a chronic illness like diabetes can be hard. Finding support from other diabetics can help you know you aren’t alone.

Kidney failure, liver disease, or severe anemiaBeing of African, Mediterranean, or Southeast Asian descentCertain blood disorders (such as sickle cell anemia or thalassemia)Certain medicines, including opioids and some HIV medicationsBlood loss or blood transfusionsEarly or late pregnancy

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