What time period does Hemoglobin A1C reflect?

Hemoglobin A1C reflects blood glucose levels over a time period of approximately 8 to 12 weeks. This test measures the percentage of hemoglobin in the blood that is glycosylated, which occurs when glucose binds to hemoglobin. Since red blood cells typically have a lifespan of about 120 days (nearly 4 months), the A1C test provides an average of blood glucose levels during that time frame. Therefore, it indicates how well blood glucose levels have been controlled over the past 2 to 3 months, making the 8 to 12 weeks timeframe the most accurate representation for the purpose of monitoring long-term glucose control in individuals, particularly those with diabetes.