**Core Concept**
The patient's presentation suggests a long-standing diabetes mellitus with complications such as diabetic retinopathy (poor vision), peripheral vascular disease, and nephropathy (mild proteinuria). Monitoring blood sugar levels is crucial to prevent further complications. Glycated hemoglobin (HbA1c) is a key marker for assessing long-term glycemic control.

**Why the Correct Answer is Right**
HbA1c is a stable protein that binds to glucose in the blood, forming a covalent bond. The level of HbA1c reflects the average blood glucose levels over the past 2-3 months. It is a more reliable indicator of blood sugar control than random or fasting glucose levels, which can fluctuate due to various factors. The American Diabetes Association recommends HbA1c as the primary marker for monitoring glycemic control in diabetic patients.

**Why Each Wrong Option is Incorrect**
**Option A:** Fasting glucose levels are not the best monitor of control as they can be influenced by factors such as stress, sleep, and medication.
**Option B:** Random glucose levels are not reliable as they can be affected by various factors, including time of day, meal consumption, and physical activity.
**Option C:** Urine glucose tests are less accurate and can be affected by kidney function, making them a poor choice for monitoring blood sugar control.

**Clinical Pearl / High-Yield Fact**
Remember that HbA1c levels can be affected by hemoglobinopathies, such as sickle cell disease or thalassemia, and by conditions that lead to red blood cell turnover, such as hemolysis.

**Correct Answer:** C. HbA1c.