**Core Concept**
Diabetes control is best monitored by measuring the glycated hemoglobin (HbA1c) level, which reflects the average blood glucose levels over the past 2-3 months. This measure is crucial for assessing the effectiveness of diabetes management and making necessary adjustments to treatment plans.

**Why the Correct Answer is Right**
HbA1c is a reliable indicator of long-term glucose control because it measures the percentage of hemoglobin molecules that have been glycated, or bound to glucose, during their lifespan. This process occurs continuously, resulting in a stable and accurate reflection of blood glucose levels. HbA1c is particularly useful for monitoring diabetic patients, as it helps identify individuals who require more aggressive treatment or closer monitoring.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because fasting blood glucose levels only provide a snapshot of blood glucose levels at a single point in time and do not account for fluctuations throughout the day.
**Option B:** Urine glucose testing is not a reliable method for monitoring diabetes control, as it only detects glucose in the urine, which may not accurately reflect blood glucose levels.
**Option C:** Blood glucose monitoring using a glucometer provides a snapshot of blood glucose levels at a single point in time and does not account for fluctuations throughout the day or long-term glucose control.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that HbA1c levels can be influenced by factors such as anemia, hemoglobinopathies, and certain medications, which can lead to inaccurate results. Therefore, it is essential to consider these factors when interpreting HbA1c levels.

**Correct Answer: A. Fasting blood glucose levels.**