Your A1c reflects your average blood sugar over the past 3 months, reported as a percent. The higher the percent, the higher your blood sugar has been. Below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or above is diabetes (NIDDK).
Key takeaways
A1c reflects your average blood sugar over the past 3 months, with the most recent 30 days counting most (NIDDK).
Below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or above is diabetes. A diagnosis needs a second test, unless there are clear symptoms of diabetes (NIDDK).
In a study of 507 people, an A1c of 7% matched an average glucose of about 154 mg/dL. Device and drug makers helped fund it (Nathan et al., 2008).
Blood loss, low iron, kidney or liver disease and some hemoglobin types can make A1c misleading (NIDDK).
What does my A1c number mean?
It's the share of your hemoglobin with sugar attached, shown as a percent. It reflects your average blood sugar over the past 3 months. A normal A1c is below 5.7%. Prediabetes is 5.7% to 6.4%, and diabetes is 6.5% or above (NIDDK).
A1c level | What it's called (NIDDK) |
|---|---|
Below 5.7% | Normal |
5.7% to 6.4% | Prediabetes |
6.5% or above | Diabetes |
NIDDK, part of the National Institutes of Health, lists these levels (NIDDK). Within the prediabetes range, the higher the A1c, the greater the risk of diabetes (NIDDK).
How does the A1c test work?
Sugar in your blood sticks to hemoglobin, the part of a red blood cell that carries oxygen. The more sugar in your blood, the more sticks. The test measures how much hemoglobin has sugar attached, which reflects your average over the past 3 months (NIDDK).
It's an uneven average. Large changes in your blood sugar over the past month show up, and the past 30 days count more than the months before. But A1c doesn't show sudden, short rises or drops (NIDDK).
The American Diabetes Association explains the time span this way: your red blood cells are replaced about every three months (ADA).
Do I need to fast for an A1c test?
No. You don't have to fast before an A1c test, so blood can be drawn at any time of day (NIDDK). That's different from a fasting glucose test, where you fast for at least 8 hours first (NIDDK). So an A1c can be part of an ordinary blood draw.
For a diagnosis, the blood should come from a vein and go to a lab that uses a certified method. Tests run in a doctor's office or clinic shouldn't be used to diagnose diabetes (NIDDK).
How does A1c turn into an average glucose?
An A1c of 7% matches an estimated average glucose of about 154 mg/dL (8.6 mmol/L). That comes from a study of 507 people, most with diabetes, partly funded by device and drug makers (Nathan et al., 2008). Some labs report this number in mg/dL, the unit home glucose meters use (NIDDK).
A1c | Estimated average glucose (Nathan et al., 2008) |
|---|---|
5% | 97 mg/dL (5.4 mmol/L) |
6% | 126 mg/dL (7.0 mmol/L) |
7% | 154 mg/dL (8.6 mmol/L) |
8% | 183 mg/dL (10.2 mmol/L) |
9% | 212 mg/dL (11.8 mmol/L) |
10% | 240 mg/dL (13.4 mmol/L) |
All figures are from Nathan et al., 2008. The study used the formula 28.7 × A1c − 46.7. It was funded by the American Diabetes Association and the European Association for the Study of Diabetes. Abbott, Bayer, GlaxoSmithKline, sanofi-aventis, Merck, Lifescan and Medtronic also gave financial support (Nathan et al., 2008).
Each number is an estimate with a spread. At 7%, the study's 95% interval ran from 123 to 185 mg/dL (Nathan et al., 2008). The estimate won't match your daily readings, because it's a long-term average (NIDDK).
Why might my A1c not match my glucose readings?
Some conditions change A1c without changing your blood sugar. Recent blood loss, sickle cell disease, a transfusion or hemodialysis can change it. Very low iron can make it falsely high. Kidney failure and liver disease can also cause false results (NIDDK).
Some people carry a hemoglobin variant, a different type of hemoglobin. It can interfere with some A1c tests and is more common in people of African, Mediterranean or Southeast Asian descent. Most people with one have no symptoms and may not know. Doctors may suspect it when A1c and glucose results don't match (NIDDK).
If you have a red blood cell condition, kidney failure or liver disease, your provider may use other tests to diagnose diabetes (MedlinePlus).
How much can A1c change between tests?
A little, even on the same blood. An A1c of 6.8% could come back anywhere from 6.4% to 7.2% if the same sample is tested again (NIDDK). That's 0.4 percentage points either way on one sample. Newer quality standards have narrowed it (NIDDK).
Blood sugar tests also differ from each other. Some people show diabetes on a glucose test but not on A1c, or the other way around. That's why doctors repeat tests before a diagnosis (NIDDK). Any single reading is one data point, the same as with everyday blood sugar swings. That's why we read your numbers against your own past (our methodology; why we compare you to you).
When is A1c not the right test?
A1c shouldn't be used to diagnose type 1 diabetes, gestational diabetes or cystic fibrosis-related diabetes (NIDDK). In pregnancy, gestational diabetes is usually checked between 24 and 28 weeks with glucose tests instead (NIDDK). In these cases, your doctor uses other tests.
What A1c target is right for people with diabetes?
For most people with diabetes, the American Diabetes Association suggests a target of 7% or less. Yours may be higher or lower, based on your health history, age and risk of low blood sugar. Work it out with your care team (ADA).
A target that's safe for one person may not be safe for another. A level between 7% and 8%, or higher, may fit some people. That includes people who've had diabetes a long time and struggle to reach a lower goal. It also includes people who have severe low blood sugar (NIDDK). Experts recommend an A1c test at least twice a year for people with diabetes (NIDDK).
Frequently asked questions
Is 5.7% bad? It's the start of the prediabetes range. Within that range, a higher A1c means a greater risk of diabetes (NIDDK). Ask your doctor what it means for you.
Can I compare my A1c from two labs? Labs often use different methods, so results from different labs can't be compared directly (MedlinePlus). There's more in how to read your lab results.
Why is my estimated average glucose different from my meter? It's a long-term average, not a reading at one moment (NIDDK).
What should I do after a high A1c? Ask your doctor what it means for you and whether to repeat it. Doctors repeat tests before a diagnosis (NIDDK). Some medicines can affect your result, so tell your provider about everything you take. Don't stop any medicine unless your provider tells you to (MedlinePlus).
Your A1c results sit in Knit's Record tab, under Lab results. These articles share patterns, not diagnoses, so talk to your doctor about anything that worries you.
