A1C Basics

What Is A1C?

An A1C (pronounced A-one-C) test reflects your average blood glucose level over the past two to three months. Even when you test your blood glucose at home as directed by your doctor, you may not capture all the ups and downs. The A1C, also known as a glycosylated hemoglobin test or HbA1c, gives a more complete picture.

The test requires a small blood sample (no fasting is necessary) that's analyzed by a laboratory. The test measures glycosylated hemoglobin, or the percentage of hemoglobin molecules in your red blood cells with glucose attached to them. Glucose naturally sticks, or glycosylates, to some of the hemoglobin in red blood cells. When blood glucose is high, more hemoglobin molecules have glucose attached to them. The glucose stays there for the life of the red blood cell (about 120 days), which is why the test covers a three-month period. About 50 percent of the reading, however, reflects just the last 30 days.