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How does the A1C test define diabetes and prediabetes?

After preliminary screening for prediabetes, laboratory tests of your fasting glucose level, oral glucose tolerance level and the A1C test will establish whether you are in the prediabetes zone or not.

In addition to those glucose levels, the American Diabetes Association (ADA) now advises that an A1C test, which does not require fasting, be used to identify prediabetes and diabetes. An A1C range of 5.7-6.4 percent puts you in the prediabetes category; a diagnosis of diabetes is made when the A1C test score is 6.5 percent or higher.

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.

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 percent 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 25 percent if diabetes is badly out of control for a long time.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.