A1C Basics

The best measure of long-term average blood glucose control is a simple laboratory test called the A1C. On-target blood glucose control helps you feel your best and prevent or delay complications.


What Is A1C?

An A1C (pronounced A-one-C) test reflects your average blood sugar or glucose level over the past two to three months. When you check your blood sugar with a meter after fasting and before or after meals, you won't capture all the ups and downs. The A1C, also known as a glycosylated hemoglobin test or HbA1c, offers you an overview to compare with your blood sugar checks.

The test requires a small blood sample (no fasting is necessary) for a lab analysis. 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.