A1C: A test that measures how much glucose has been sticking during the past 3-4 months to hemoglobin, the substance in the red blood cells that carries oxygen to the cells of the body. The A1C test is important in diabetes as a long-term measure of control over blood glucose. Even outside of diabetes, an elevated A1C level may be a cardiovascular risk factor.

For more information about A1C, see: Hemoglobin A1C.