HbA1c reflects average blood glucose concentration over which approximate time frame?

• A. 1-3 weeks
• B. 4-5 weeks
• C. 6-8 weeks
• D. 16-20 weeks

Answer: (C)

HbA1c measures long-term glycemic exposure because hemoglobin becomes glycated as red blood cells circulate. Since the average red blood cell life is about 120 days, the HbA1c level accumulates glycated hemoglobin over weeks to months, reflecting overall glucose levels rather than a single day. Among the given options, six to eight weeks is the best approximate window—it corresponds to the period over which the majority of circulating red cells contribute to the HbA1c signal. Shorter intervals (1–3 weeks or 4–5 weeks) would miss the contribution from older cells, while a much longer window (16–20 weeks) exceeds typical clinical relevance. In practice, HbA1c is often described as reflecting roughly two to three months of glucose history, but within these choices, six to eight weeks is the closest match.