- The A1C test measures your average blood glucose control for the past 2 to 3 months.
- It is determined by measuring the percentage of glycated hemoglobin, or HbA1c, in the blood.
- Check your A1C twice year at a minimum, or more frequently when necessary.
- It does not replace daily self-testing of blood glucose.
Checking your blood glucose at home with a meter tells you what your blood sugar level is at any one time, but suppose you want to know how you're doing overall.
The A1C test gives you a picture of your average blood glucose control for the past 2 to 3 months. The results give you a good idea of how well your diabetes treatment plan is working.
In some ways, the A1C test is like a baseball player's season batting average, it tells you about a person's overall success. Neither a single day's blood test results nor a single game's batting record gives the same big picture. You may also be interested in our book, 50 Things You Need to Know About Diabetes.
How Does A1C Help Diabetes Control?
These are some ways the A1C test can help you manage your diabetes:
- Confirm self-testing results or blood test results by the doctor.
- Judge whether a treatment plan is working.
- Show you how healthy choices can make a difference in diabetes control.
How Does it Work?
Hemoglobin, a protein that links up with sugars such as glucose, is found inside red blood cells. Its job is to carry oxygen from the lungs to all the cells of the body.
When diabetes is uncontrolled, you end up with too much glucose in the bloodstream. This extra glucose enters your red blood cells and links up (or glycates) with molecules of hemoglobin. The more excess glucose in your blood, the more hemoglobin gets glycated. By measuring the percentage of A1C in the blood, you get an overview of your average blood glucose control for the past few months.
How Does the A1C Test Look Backward?
Suppose your blood sugar was high last week. What happened? More glucose hooked up (glycated) with your hemoglobin. This week, your blood glucose is back under control.
Still, your red blood cells carry the "memory" of last week's high blood glucose in the form of more A1C.
This record changes as old red blood cells in your body die and new red blood cells (with fresh hemoglobin) replace them. The amount of A1C in your blood reflects blood sugar control for the past 120 days, or the lifespan of a red blood cell.
In a person who does not have diabetes, about 5% of all hemoglobin is glycated. For someone with diabetes and high blood glucose levels, the A1C level is higher than normal. How high the A1C level rises depends on what the average blood glucose level was during the past weeks and months.
Levels can range from normal to as high as 15% or more if diabetes is badly out of control for a long time.
You should have had your A1C level measured when your diabetes was diagnosed or when treatment for diabetes was started. To watch your overall glucose control, your doctor should measure your A1C level at least twice a year.
There are times when you need to have your A1C level tested about every 3 months. If you change diabetes treatment, such as start a new medicine, or if you are not meeting your blood glucose goals, you and your doctor will want to keep a closer eye on your control.
What are the Limitations?
Although the A1C test is an important tool, it can't replace daily self-testing of blood glucose for those who need it. A1C tests don't measure your day-to-day control. You can't adjust your insulin on the basis of your A1C tests. That's why your blood sugar checks and your log of results are so important to staying in effective control.
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