A patient asks why the doctor ordered an HbA1C test instead of just checking fasting blood sugar. The nurse's best response is:

Rationale: A. HbA1C reflects average blood glucose over approximately 2–3 months by measuring the percentage of hemoglobin molecules that are glycated. This provides a long-term view of glucose control, helping guide therapy adjustments and predict risk for complications such as retinopathy, nephropathy, and neuropathy. B. HbA1C does not measure ketones. Ketone testing is performed via urine dipstick or blood beta-hydroxybutyrate, which is used to detect ketoacidosis, not long-term glucose control. C. Fasting blood glucose or point-of-care glucose testing reflects current blood sugar, not long-term control. HbA1C provides a historical average, rather than a single snapshot. D. HbA1C does not measure pancreatic function or insulin production. Tests such as C-peptide or insulin levels are used to assess endogenous insulin production.