After starting treatment for type 2 diabetes mellitus 6 months earlier, a patient is in the office for a follow-up examination. The nurse will monitor which laboratory test to evaluate the patient's adherence to the antidiabetic therapy over the past few months?

Choice A rationale: Hemoglobin levels, which are the total amount of hemoglobin protein in the blood, are primarily used to assess for anemia. While chronic hyperglycemia can lead to protein glycation, including hemoglobin, the direct measurement of total hemoglobin does not provide a long-term average of blood glucose control. Normal hemoglobin levels for adults range from 13.5 to 17.5 g/dL for men and 12.0 to 15.5 g/dL for women. Choice B rationale: Hemoglobin A1C measures the percentage of hemoglobin that has become glycated, or bound to glucose, over the lifespan of red blood cells. Since red blood cells live for approximately 120 days, this test provides an average of blood glucose levels over the preceding two to three months. This makes it a reliable indicator for assessing a patient's long-term glycemic control and adherence to antidiabetic therapy. Normal A1C levels are below 5.7%. Choice C rationale: A fingerstick fasting blood glucose level provides an immediate snapshot of the patient's blood glucose at a single point in time after a period of fasting. While useful for daily monitoring and adjusting medication dosages, it is not a reliable indicator of long-term glycemic control or adherence to therapy over the past several months. The normal range for fasting blood glucose is 70 to 100 mg/dL. Choice D rationale: Serum insulin levels reflect the amount of insulin circulating in the blood at the time of the test. This measurement can be used to assess pancreatic function and determine if the patient is producing insulin. However, it does not provide a historical average of blood glucose control over an extended period. Its utility in monitoring long-term therapy adherence is limited compared to A1C.