Which symptom indicates a potential complication for a patient with diabetes mellitus?

Changes in vision indicate a potential complication for a patient with diabetes mellitus because they can signal diabetic retinopathy, a serious condition that can arise from uncontrolled blood sugar levels over time. Diabetic retinopathy involves damage to the blood vessels in the retina, leading to symptoms such as blurred vision, floaters, and even vision loss if not addressed. Regular monitoring of vision is essential for patients with diabetes, as early detection of any changes can lead to timely treatment and prevent severe complications.

Other symptoms, while significant and indicative of diabetes management issues, do not directly signal acute complications. Dry skin, excessive thirst, and frequent urination are more indicative of poorly controlled diabetes due to high blood sugar levels but do not immediately signify the risk of irreversible damage that changes in vision represent. Thus, changes in vision are a critical warning sign of potential long-term complications associated with diabetes.