If you have diabetes, it is important to know what the A1C (sometimes called ‘hemoglobin A1C’) test is, and how the diabetes team uses the A1C. This includes determining whether the person living with diabetes is on the best treatment and what their target A1C should be to avoid complications.
Question: What is an A1C blood test? (don’t peak at the answer!)
Answer: The A1C is a blood test that is done any time of day (doesn’t have to be fasting). It is a measure of the level of glucose in the blood for the past 3 months. It reflects the past 3 months because it is measuring the sugar coating on the red blood cells. The red blood cells don’t have anything to do with diabetes but how covered they are with sugar is handy as they are made and destroyed about every 3 months. The A1C is used to follow the person’s blood sugar control and it is also used to diagnose diabetes.
How does the A1C relate to average blood sugar?
The A1C measurement is done in percent, (for example 7 %). It does not mean the blood sugar has been 7 mmol/L (the number a person would get from their glucometer). However, there is a formula that converts the A1C to an average blood sugar.
Canada uses mmol/L for blood sugar
|A1C (%)||Average Blood Sugar (mMol/L)|
What A1C number is used to diagnose diabetes?
When an A1C is equal to or greater than 6.0%, this is diagnosed as pre-diabetes, and when it is equal to or greater than 6.5% this is a diagnosis of diabetes. (The test should always be repeated on a different day to be sure of the diagnosis.)
What is the target A1C for a person with diabetes?
For most people, the target should be 7% (This is usually attained by having a pre-meal blood sugar of 4-7 mmol/L and post-meal blood sugar of 5-10 mmol/L). If a person is very elderly or frail, a young child, or someone at risk of having low blood sugars, then the A1C can be 8% or 8.5 %. It is important to individualize the A1C by talking to the diabetes team.
What does it mean when the A1C and the blood sugars don’t match?
Sometimes a person’s A1C doesn’t seem to match their blood sugar readings.
If this is the case, it usually means that they are not measuring their blood sugars often enough to see the fluctuation in blood sugars. For example, an A1C might be elevated (for example 9%) but the person gets very normal readings in the morning (7 mmol/L). However, they are not testing later in the day when their readings might be 12 mmol/L.
Is the A1C ever inaccurate?
The A1C can be inaccurate if there is a problem with the red blood cells. For instance, if the person is very anemic or has mis-shaped red blood cells like sickle cells. Also kidney and liver disease make the A1C less representative of the average blood sugar.
Why does a person need to test their blood sugars if they can get an A1C?
The A1C is only an “average” blood sugar reading. This can be made up of highs and lows. If someone is on a treatment that doesn’t cause lows (for example, only metformin), then they don’t need to do blood tests as often and the A1C is fairly representative of their average blood sugar. However, blood testing will give specific information on the ‘pattern‘ of their blood sugars, showing when they are high and what foods cause them to be higher or lower.
If a person is on insulin, then testing can give moment-to-moment information on how to adjust insulin. If a person’s A1C is out of range, then testing gives information on what time of day to target therapy. For instance, if the morning numbers are higher, they may need nighttime insulin or if the morning numbers are at target but they are high after supper, they may need more medication at suppertime.