What Is A1C?
A1C is an estimate of average blood sugar over the past 2 to 3 months and is usually tested during health care appointments. Simply put, it is like a “memory” of blood sugar levels. It’s a standard laboratory blood test that shows how well blood sugar is being controlled over time. A1C and regular blood sugar monitor readings are different ways to tell how well someone’s diabetes is being managed.
Examples of A1C levels and how they relate to average blood sugar levels
Many times when A1C results come back from the lab, there is another blood sugar reading next to it that looks more like what you would see on a regular blood sugar meter. It is called the estimated average glucose (eAG). The eAG is another way of showing the average blood sugar levels, using the same measurement that is on blood sugar meters: mg/dL (milligrams per deciliter).
Here is how A1C numbers and estimated average blood sugar (glucose) readings match up:
Estimated Average Glucose (mg/dL)
Adapted from the ADA Standards of Medical Care in Diabetes—2016.
How often is an A1C test needed? It depends on how controlled and stable blood sugar has been. If you are meeting the treatment goals set by your diabetes care team, the A1C test should be done at least 2 times a year. However, if you are not meeting your blood sugar goals, or your therapy has changed, A1C testing may be necessary up to 4 times a year.
Sometimes, A1C results don’t seem to really match the daily finger-stick blood sugar checks. Blood sugar readings from a meter show snapshots in time, where the A1C reflects an average of ongoing blood sugar levels.
- An A1C that is much higher than expected, based on usual pre-meal meter readings, may be a sign of after-meal or overnight high blood sugar levels
- An A1C that is much lower than expected, based on usual pre-meal meter readings, may show that low blood sugar is happening too often and may be occurring without any symptoms
If the A1C test results don’t seem to match what is written in the Blood Sugar Tracker, make sure to mention it to the diabetes care team.