While a serum glucose measures the glucose level right now, measuring the hemoglobin A1C tells us how well the glucose has been managed over the last three months.

A1C is a blood test for type 2 diabetes and prediabetes. It measures your average blood glucose, or blood sugar, level over the past 3 months. Doctors may use the A1C alone or in combination with other diabetes tests to make a diagnosis. They also use the A1C to see how well you are managing your diabetes.