What is a hemoglobin A1C test and what is the target level?

Hemoglobin A1C, also called glycosylated hemoglobin, measures the percentage of hemoglobin with glucose attached, reflecting average blood glucose control over the past two to three months, which matches the lifespan of red blood cells. The target A1C for most diabetic adults is below 7 percent, which correlates with an estimated average glucose of about 154 milligrams per deciliter. An A1C of 6.5 percent or higher on two separate tests is diagnostic for diabetes. An A1C between 5.7 and 6.4 percent indicates prediabetes.