Which of the following lab tests would be the most direct indicator of long-term glucose control?

The Hemoglobin A1c test serves as the most direct indicator of long-term glucose control because it measures the average blood glucose levels over the past two to three months. This test reflects how much glucose has been attached to hemoglobin in the red blood cells over time, providing a comprehensive view of a person's blood sugar levels rather than just a snapshot.

In contrast, the random glucose test measures glucose levels at a specific point in time and is affected by recent food intake and other factors. The fasting glucose test requires fasting and looks at blood sugar levels after not eating for a certain period, which does not reflect long-term glucose management. The oral glucose tolerance test is primarily used to diagnose diabetes and assesses the body's response to glucose over a short period rather than over the months that the A1c test covers. Thus, the A1c test is the most reliable for tracking long-term glycemic control, making it a standard recommendation for managing diabetes.