Glycated hemoglobin (HbA1c) tests, mean glucose levels

Correct option is D

HbA1c measures the percentage of glucose bound to hemoglobin and reflects average blood glucose levels over the past 8 to 12 weeks, or approximately 90 days. It is widely used for diagnosing and monitoring diabetes. The result is not affected by short-term fluctuations and gives a more reliable long-term picture of glycemic control.
Explanation of each option: • (a) Over 2 days – This duration is too short for HbA1c to reflect; daily blood sugar changes are captured through capillary blood glucose tests or self-monitoring. HbA1c cannot assess such brief fluctuations. • (b) Over 14 days – This period is better assessed by fructosamine levels, which measure glycation of serum proteins. HbA1c reflects a much longer duration. • (c) Over 30 days – Still an underestimation of the actual timeframe. While partial influence exists from the last month’s sugar levels, HbA1c gives an average over 3 months, not just one. • (d) Over 90 days – Correct. This matches the lifespan of red blood cells (~120 days), which is why HbA1c reflects glucose exposure over about 3 months.