A high A1c means your blood sugar has been elevated over the past two to three months. The A1c test measures the percentage of hemoglobin (a protein in red blood cells) that has glucose attached to it. A normal result is below 5.7%, a reading between 5.7% and 6.4% indicates prediabetes, and 6.5% or higher is used to diagnose diabetes.
How the A1c Test Works
Glucose in your bloodstream naturally sticks to hemoglobin inside red blood cells. The more sugar circulating in your blood, the more hemoglobin gets coated. Because red blood cells live about three months before your body replaces them, the A1c reading captures a rolling average of your blood sugar over that entire lifespan. This makes it more useful than a single finger-stick glucose reading, which only tells you what’s happening in that moment.
You can translate an A1c percentage into an estimated average glucose (eAG) in mg/dL using a simple formula: multiply your A1c by 28.7, then subtract 46.7. For example, an A1c of 7% corresponds to an average blood sugar around 154 mg/dL. At 8%, that average jumps to about 183 mg/dL. At 9%, it’s roughly 212 mg/dL. These numbers help put the abstract percentage into the same units you see on a glucose meter.
What the Numbers Mean
The American Diabetes Association defines three ranges:
- Below 5.7%: Normal blood sugar regulation.
- 5.7% to 6.4%: Prediabetes, meaning blood sugar is higher than normal but not yet in the diabetes range. This is the window where lifestyle changes can have the biggest impact.
- 6.5% or higher: Diabetes. A second confirmatory test is typically done before a formal diagnosis.
These thresholds apply to most adults, but your personal target may differ. Guidelines from the American College of Physicians emphasize that A1c goals should be individualized based on your overall health, life expectancy, risk of low blood sugar episodes, and personal preferences. A stricter target may make sense for someone expected to live at least 15 more years. For adults over 80 or those with serious chronic conditions, the priority shifts to managing symptoms rather than hitting a specific number.
Symptoms You Might Notice
A mildly elevated A1c, especially in the prediabetes range, often causes no obvious symptoms at all. That’s part of what makes it tricky. Many people learn about a high reading during routine bloodwork and feel completely fine.
When blood sugar stays consistently high, though, the body starts sending signals. Early signs include increased thirst, frequent urination, headaches, and blurred vision. These happen because excess glucose pulls water from your tissues, making you dehydrated and forcing your kidneys to work harder. Over longer periods, persistent high blood sugar can cause fatigue, unexplained weight loss, slow-healing cuts, recurring skin infections, and vaginal yeast infections. If you’ve noticed several of these together, it’s worth getting your A1c checked.
Why a High A1c Matters Long-Term
Sustained high blood sugar damages blood vessels and nerves throughout the body. The complications fall into two broad categories: damage to large blood vessels (heart, brain, major arteries) and damage to small blood vessels (eyes, kidneys, nerve endings in your hands and feet).
Cardiovascular risk rises meaningfully once A1c climbs above roughly 7.2%. A large Danish registry study of over 27,000 people with diabetes found that the risk of major cardiovascular events, including heart attack and stroke, increased significantly at A1c levels of 7.2% and above. The risk of microvascular complications, the kind that affect your eyes, kidneys, and nerves, also increased at that same threshold. This doesn’t mean damage starts at exactly 7.2% and not a decimal point before, but it illustrates that the higher your A1c climbs, the more your risk compounds over time.
Nerve damage in the feet can lead to numbness, tingling, or burning pain. Damage to the tiny blood vessels in the retina can gradually impair vision. Kidney function can decline. None of these complications happen overnight. They develop over years of poorly controlled blood sugar, which is exactly why catching a high A1c early gives you time to change course.
Lowering Your A1c
The most effective approach combines dietary changes, physical activity, and weight management. In a meta-analysis of lifestyle intervention studies, people who adopted combined strategies (better diet, more movement, and weight control) saw meaningful reductions in A1c. The changes don’t need to be dramatic to make a difference. Even modest, sustained improvements in daily habits move the needle.
On the dietary side, reducing refined carbohydrates and added sugars has the most direct effect on blood sugar. Swapping white bread, sugary drinks, and processed snacks for whole grains, vegetables, lean proteins, and healthy fats helps blunt the blood sugar spikes that drive A1c upward. You don’t need to follow a specific named diet. The core principle is eating fewer foods that rapidly raise blood sugar.
Exercise helps in two ways. During activity, your muscles pull glucose from the bloodstream for energy, immediately lowering blood sugar. Over time, regular exercise also improves your cells’ sensitivity to insulin, meaning your body handles glucose more efficiently even at rest. Both aerobic activity (walking, cycling, swimming) and resistance training (weights, bodyweight exercises) contribute. Aiming for 150 minutes per week of moderate activity is a widely used benchmark.
For people with type 2 diabetes whose A1c remains high despite lifestyle changes, medication can help. Some medications work by making your body more responsive to insulin, others stimulate the pancreas to produce more insulin, and newer classes slow glucose absorption or increase how much sugar your kidneys excrete. Your treatment plan depends on how high your A1c is, how long you’ve had diabetes, and how your body responds.
When the Test Can Be Misleading
The A1c test is reliable for most people, but certain conditions can skew results in either direction. Iron deficiency anemia, which is common during late pregnancy, can push A1c readings artificially higher. On the other hand, conditions that shorten the lifespan of red blood cells, like hemolytic anemia or recovery from significant blood loss, can make A1c look falsely low because the red blood cells haven’t been around long enough to accumulate glucose.
Sickle cell disease and other hemoglobin variants also interfere with accuracy. The abnormal hemoglobin and increased red blood cell turnover in these conditions make the A1c unreliable enough that alternative tests, such as glycated albumin, are recommended instead. Chronic kidney disease, particularly in people on dialysis, tends to cause A1c to underestimate actual blood sugar levels. If you have any of these conditions and your A1c results don’t seem to match how you feel or what your glucose meter shows, there are other ways to monitor long-term blood sugar control.