The A1C test measures your average blood sugar over the past two to three months, and the results fall into three main ranges: below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or above means diabetes. These cutoffs, established by the American Diabetes Association, are the standard used by doctors to screen for and diagnose type 2 diabetes.
How the A1C Test Works
When sugar circulates in your bloodstream, some of it attaches to hemoglobin, the protein inside red blood cells that carries oxygen. The more sugar in your blood over time, the more hemoglobin gets coated. The A1C test measures what percentage of your hemoglobin has sugar stuck to it.
Because red blood cells live about 90 to 120 days before your body replaces them, the test captures a rolling average of your blood sugar over roughly the last two to three months. This makes it more useful than a single finger-stick glucose reading, which only shows what your blood sugar is doing at that exact moment. You don’t need to fast before an A1C test, and it can be drawn at any time of day.
The Three Diagnostic Ranges
Normal (below 5.7%): Your blood sugar regulation is working well. No follow-up testing is specifically needed for diabetes, though your doctor may include it in routine checkups.
Prediabetes (5.7% to 6.4%): Your blood sugar is higher than normal but not yet in the diabetes range. Around 80 million American adults fall into this category. Prediabetes is reversible with lifestyle changes like losing 5% to 7% of body weight and getting regular physical activity. If you’re in this range, retesting once a year is typical.
Diabetes (6.5% or above): This level, confirmed on a repeat test, meets the diagnostic threshold for diabetes. The higher the number, the greater the amount of sugar coating your red blood cells, and the higher your risk for complications affecting your eyes, kidneys, nerves, and heart.
What A1C Translates to in Daily Blood Sugar
A1C percentages can feel abstract. A useful way to think about your result is to convert it to estimated average glucose (eAG), the number you’d see on a blood sugar meter, measured in mg/dL. The conversion formula is: A1C × 28.7 − 46.7 = eAG.
Here are some common reference points:
- A1C of 5.7% = roughly 117 mg/dL
- A1C of 6.0% = about 126 mg/dL
- A1C of 6.5% = about 140 mg/dL
- A1C of 7.0% = about 154 mg/dL
- A1C of 8.0% = about 183 mg/dL
- A1C of 9.0% = about 212 mg/dL
- A1C of 10.0% = about 240 mg/dL
These numbers represent averages, so your actual blood sugar swings higher after meals and lower between them. Two people with the same A1C can have very different daily patterns.
Target Ranges for People With Diabetes
Once you have a diabetes diagnosis, the goal shifts from diagnosis to management, and the target A1C isn’t the same for everyone. For most nonpregnant adults, the general recommendation is below 7%. That corresponds to an average blood sugar of about 154 mg/dL.
Some people can safely aim tighter. If you were recently diagnosed, are younger, and don’t have significant heart disease, a target below 6.5% may be reasonable, as long as it doesn’t cause frequent episodes of dangerously low blood sugar (hypoglycemia). On the other hand, a more relaxed target of below 8% is often appropriate for people who are older, have had diabetes for many years, or have other serious health conditions. For adults over 80 or those with limited life expectancy, the priority shifts toward simply avoiding the symptoms of high blood sugar, like excessive thirst, frequent urination, and fatigue, rather than hitting a specific number.
The factors that shape your personal target include how long you’ve had diabetes, your risk for low blood sugar episodes, your overall health, and how complex your treatment plan is. A single A1C cutoff doesn’t fit everyone, which is why guidelines emphasize personalized goals.
A1C Targets During Pregnancy
Pregnancy calls for tighter blood sugar control because elevated glucose raises the risk of birth defects, preeclampsia, preterm delivery, and the baby growing too large. For women with preexisting diabetes who are pregnant or planning to become pregnant, the ideal A1C is below 6%, or below 6.5% before conception. If reaching that level causes too many low blood sugar episodes, a target below 7% is considered acceptable.
One important caveat: A1C isn’t the preferred tool for diagnosing gestational diabetes or for postpartum screening after gestational diabetes. Pregnancy increases the rate at which red blood cells turn over, and blood loss during delivery further skews the reading. An oral glucose tolerance test is more reliable in those situations.
When A1C Results Can Be Misleading
The test assumes your red blood cells have a normal lifespan and that your hemoglobin is the standard type. Several conditions break those assumptions and can produce inaccurate results.
Sickle cell trait, which affects roughly 1 in 13 Black Americans, is one of the most significant. According to the CDC, people with sickle cell trait can get A1C readings that are falsely low or falsely high, depending on the testing method used. A normal result in someone with sickle cell trait doesn’t reliably rule out diabetes. Other hemoglobin variants, common in people of Mediterranean, Southeast Asian, and African descent, can cause similar problems.
Conditions that shorten the life of red blood cells, such as iron-deficiency anemia, blood loss, or kidney disease requiring dialysis, tend to pull A1C readings lower than the true average. Conversely, conditions that extend red blood cell lifespan, like iron-deficiency without active blood loss, can push readings higher. If your doctor suspects your A1C doesn’t match your daily glucose readings, alternative tests like fructosamine or continuous glucose monitoring may give a clearer picture.
How Often to Get Tested
Testing frequency depends on where you fall on the spectrum. If you have prediabetes, once a year is standard. If you have diabetes and your blood sugar is well controlled without insulin, twice a year is typical. You’ll likely need more frequent testing if you use insulin, recently changed medications, or are having difficulty staying within your target range. In those cases, testing every three months helps track whether adjustments are working.