HbA1c measures which of the following EXCEPT:

Correct answer: D. Status of glucose during the last 6 months

• A. INCORRECT (this IS what HbA1c measures). HbA1c reflects average blood glucose over the past 2–3 months, corresponding to the lifespan of red blood cells (~90 days). This is its primary clinical utility.
• B. INCORRECT (this IS what HbA1c measures). HbA1c specifically measures the percentage of hemoglobin molecules that have glucose irreversibly bound to them — the higher the blood glucose, the more glycated hemoglobin.
• C. INCORRECT (this IS what HbA1c measures). HbA1c is the gold standard for monitoring long-term glycemic control and treatment effectiveness in diabetic patients.
• D. CORRECT — this is the EXCEPTION. HbA1c does NOT measure glucose status over the last 6 months. It reflects the past 2–3 months (approximately 90 days), which corresponds to the average lifespan of a red blood cell. The 6-month timeframe is clinically inaccurate and is the exception here.