Diabetes Home > A1c Basics for People With Type 2 Diabetes

The A1c test measures how well a person with type 2 diabetes is controlling their blood sugar over time. It is usually done every three months or so, but may be done more often if you are changing to a new medication, for example. Ask your doctor what your goal A1c should be, and understand the factors that may cause the number to be higher or lower than you expected.


A1c: The Basics

If you already have type 2 diabetes, you have no doubt already heard quite a bit about the A1c test. But, just in case it's been awhile, we'll start with the basics. The A1c test is used to measure long-term blood sugar control. It gives an average of sorts of your blood sugar over a period of about three months. It is a blood test and is used to both screen for and monitor type 2 diabetes. Although it is a very useful test, it does have some limitations.

The Science Behind A1c

Some of the glucose ("sugar") in the bloodstream permanently attaches to hemoglobin, a protein in red blood cells. The lifespan of a red blood cell is about 120 days, more or less. By measuring the percentage of hemoglobin molecules attached to glucose, this test gives a picture of average blood glucose levels over a period of about three months. This is very useful for monitoring how you are doing with medications, lifestyle changes, and other efforts to control your blood sugar. It can also be used to screen for type 2 diabetes, although other tests might be better for screening in some circumstances.
Once you understand how the test works, it's easy to see why getting an A1c test done more often than every three months doesn't make much sense. How often should you get tested if you have type 2 diabetes? You'll need more frequent tests (such as four times a year) if you are making changes such as new medications or aren't at your goal. If you're near your goal and your health and your diabetes care regimen is stable, less frequent testing (maybe once a year) is probably fine.
You don't need to fast for your A1c test unless you're also having other tests done at the same time that require fasting.
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Last reviewed by: Arthur Schoenstadt, MD
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