A1c vs daily blood sugar readings: what is the difference?
A1c shows your average blood glucose over about the last three months, as a percentage. A daily reading shows your glucose at one moment, in mg/dL or mmol/L. They answer different questions, which is why many care teams look at both.
What does A1c measure?
A1c (also called HbA1c or glycated haemoglobin) shows your average blood glucose over about the last three months. It is reported either as a percentage (the US and many other countries) or in mmol/mol (the UK and much of Europe). See the A1c converter to switch between them.
What do daily blood sugar readings show?
A reading from a finger-prick meter or a sensor shows your glucose at that moment. It can rise and fall within hours after food, activity, stress or medicine. Daily readings show these ups and downs. A1c does not.
What is estimated average glucose (eAG)?
Researchers compared A1c with thousands of glucose measurements and found a consistent relationship. The estimated average glucose (eAG) is the average glucose that goes with an A1c value. In mg/dL it is 28.7 × A1c − 46.7.
| A1c (%) | A1c (mmol/mol) | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|---|
| 5.0 | 31 | 97 | 5.4 |
| 5.5 | 37 | 111 | 6.2 |
| 6.0 | 42 | 126 | 7.0 |
| 6.5 | 48 | 140 | 7.8 |
| 7.0 | 53 | 154 | 8.6 |
| 7.5 | 58 | 169 | 9.4 |
| 8.0 | 64 | 183 | 10.2 |
| 8.5 | 69 | 197 | 11.0 |
| 9.0 | 75 | 212 | 11.8 |
| 10.0 | 86 | 240 | 13.4 |
| 11.0 | 97 | 269 | 14.9 |
| 12.0 | 108 | 298 | 16.5 |
Why might the numbers not match?
- A1c covers about three months. A meter average covers only the moments you tested.
- Large swings can average out to the same A1c as steady readings.
- Some conditions, such as certain blood disorders or recent blood loss, can affect A1c accuracy. Your care team can tell you if this applies to you.
What are the standard A1c categories?
According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), an A1c below 5.7% is normal, 5.7% to 6.4% is prediabetes and 6.5% or above is diabetes. A diagnosis needs a clinician. The A1c that is right for you is set with your care team.
Information, not medical advice. Talk to your care team about your own targets and treatment. Never use a converter or a diary entry to work out an insulin or medicine dose.
Sources
- NIDDK: Diabetes tests and diagnosis
- Nathan et al., Diabetes Care, 2008: Translating the A1C assay into estimated average glucose values
- NGSP: IFCC standardization and conversion
Frequently asked questions
Why does my A1c not match my meter average?
A1c reflects about three months and is weighted toward recent weeks, while a meter average covers only the times you tested. Certain health conditions can also affect A1c accuracy, so ask your care team.
How often is A1c measured?
Your care team decides, based on your type of diabetes and treatment. Many people have it checked a few times a year.
What are the standard A1c categories?
According to the NIDDK, below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or above is diabetes. Only a clinician can diagnose diabetes.
Keep reading
A1c converter
Convert A1c between percent (NGSP) and mmol/mol (IFCC) and see the estimated average glucose. Free, private, with formulas and sources.
Blood sugar basicsGMI explained
The glucose management indicator (GMI) estimates A1c from the average glucose on a CGM. The formula, a table and why it can differ from your lab A1c.
Blood sugar basicsTime in range
Time in range is the share of the day your glucose stays between 70 and 180 mg/dL. How it is calculated and what the international consensus says.