Monitoring long term glucose control in patients with adult onset diabetes mellitus can best be accomplished by measuring:

• A. weekly fasting 7 am serum glucose
• B. glucose tolerance testing
• C. 2 hr. postprandial serum glucose
• D. hemoglobin A1c

Answer: (D)

Measuring hemoglobin A1c provides a readout of average blood glucose over the previous two to three months because glucose irreversibly attaches to hemoglobin in red blood cells as they circulate. Since red blood cells live about 120 days, the HbA1c percentage reflects mean glucose exposure over that period, making it the best test for long-term glycemic control in adults with diabetes. The other options are short-term or diagnostic snapshots: a single weekly fasting glucose shows only a momentary level; glucose tolerance testing is used mainly to diagnose or assess glucose handling, not to monitor ongoing control; a two-hour postprandial glucose reflects a post-meal spike at one time point. So HbA1c best informs how well long-term glucose control is being maintained. Be aware that conditions affecting red blood cell turnover can affect HbA1c accuracy, but otherwise it’s the standard for monitoring chronic control.