An A1C level is a blood test result that shows your average blood sugar over the past two to three months, expressed as a percentage. Below 5.7% is considered normal, 5.7% to 6.4% falls in the prediabetes range, and 6.5% or higher indicates diabetes. Unlike a standard blood sugar check that captures a single moment, the A1C gives a broader picture of how your body has been handling glucose over time.
How the A1C Test Works
The test measures how much glucose has attached to hemoglobin, the protein inside red blood cells that carries oxygen. When blood sugar rises, glucose naturally sticks to hemoglobin, and it stays there for the entire lifespan of the red blood cell. Since red blood cells live about three months, the percentage of hemoglobin coated in glucose reflects your average blood sugar over that window. A higher percentage means your blood sugar has been running higher on average.
This is why the A1C is sometimes called a “big picture” test. A fasting blood sugar test tells you what your glucose is doing right now. The A1C tells you what it’s been doing all season.
What the Numbers Mean
The A1C result is reported as a percentage. Here’s how the ranges break down:
- Below 5.7%: Normal blood sugar regulation. No signs of prediabetes or diabetes.
- 5.7% to 6.4%: Prediabetes. Blood sugar has been higher than normal but not yet in the diabetes range. This is the window where lifestyle changes can make the biggest difference.
- 6.5% or higher: Diabetes. A second test is typically done to confirm the diagnosis.
For people already managing diabetes, the American Diabetes Association suggests a target A1C of 7% for most nonpregnant adults. That corresponds to an estimated average glucose (eAG) of about 154 mg/dL, which is the same unit you’d see on a home glucose meter or continuous glucose monitor. Your doctor may set a slightly different target based on your age, health, and risk of low blood sugar episodes.
A1C Translated to Daily Blood Sugar
One reason A1C percentages can feel abstract is that they don’t match the numbers you see on a glucose meter. The eAG conversion helps bridge that gap. An A1C of 6% translates to an average blood sugar of roughly 126 mg/dL. At 7%, it’s about 154 mg/dL. At 8%, roughly 183 mg/dL. Each percentage point increase represents a jump of about 29 mg/dL in average blood sugar.
Seeing the number in mg/dL makes it easier to connect your A1C result to the readings you track day to day. If your meter consistently shows numbers in the 150s, for example, you’d expect your A1C to land around 7%.
No Fasting Required
Unlike a fasting glucose test, the A1C doesn’t require you to skip meals beforehand. Because it measures glucose that has accumulated on red blood cells over months, what you ate for breakfast won’t change the result. That said, your doctor may order other bloodwork at the same visit (like a cholesterol panel) that does require fasting, so it’s worth checking ahead of time.
How Often You Should Get Tested
If your levels are normal and you have no risk factors, the A1C is typically part of routine bloodwork every few years. For people with prediabetes, testing once a year helps track whether blood sugar is creeping upward or responding to changes in diet and activity. People with diabetes generally get tested two to four times a year, depending on how stable their blood sugar has been and whether they’ve recently changed their treatment plan.
When the A1C Can Be Misleading
The test is reliable for most people, but certain conditions can skew the results. Anything that changes the lifespan of red blood cells will throw off the reading. Conditions that destroy red blood cells faster than normal, like hemolytic anemia or significant blood loss, shorten the time glucose has to accumulate on hemoglobin. The result: a falsely low A1C that makes blood sugar control look better than it actually is.
Iron deficiency anemia works in the opposite direction. It’s associated with artificially higher A1C readings, even in people without diabetes. This is especially relevant during late pregnancy, when iron deficiency is common and can push A1C numbers up in otherwise healthy individuals.
Genetic hemoglobin variants, which are more common in people of African, Mediterranean, or Southeast Asian descent, can also affect accuracy depending on the lab method used. Sickle cell trait (HbS) and hemoglobin C trait are two well-known examples. People with sickle cell disease face compounded issues: anemia, faster red blood cell turnover, and potential transfusions all interfere with the test’s ability to reflect true blood sugar averages. Chronic kidney disease, particularly in people on dialysis, can similarly cause the A1C to underestimate actual glucose levels.
If any of these conditions apply to you, your doctor may rely on alternative measures, such as a fructosamine test or glycated albumin, to get a more accurate picture of your blood sugar trends.
What a Prediabetes Result Means in Practice
An A1C in the 5.7% to 6.4% range doesn’t mean diabetes is inevitable. It means your body is having a harder time keeping blood sugar in the normal range, and the trajectory matters more than the single number. Losing 5% to 7% of body weight and getting about 150 minutes of moderate activity per week has been shown to cut the risk of progressing to type 2 diabetes by more than half. Retesting in a year shows whether those changes are moving the number in the right direction.