Hemoglobin A1c (HbA1c) is glycated hemoglobin, which forms when hemoglobin within red blood cells joins with glucose. HbA1c levels reflect the average blood glucose level during the preceding 2 - 3 months. This differs from a blood glucose test, which measures the concentration of glucose at only the point at which the blood sample was collected.
One benefit of HbA1c is that measurements are required significantly less often compared to standard blood glucose tests. When HbA1c is used for monitoring glucose control in pre-diabetic and diabetic individuals, testing is typically done twice yearly in well controlled patients and four times yearly in poorly controlled individuals. More frequent measurements are not necessary and will not provide any additional information on blood glucose levels.