**Core Concept**
The presence of glycosuria (sugar in the urine) in a patient with normal fasting and postprandial blood sugar levels suggests an issue with renal glucose reabsorption. This is a classic case of renal glucose loss, which can occur due to various reasons.

**Why the Correct Answer is Right**
The kidneys normally reabsorb glucose back into the bloodstream. However, in conditions like Fanconi syndrome or renal tubular acidosis (RTA), the renal tubules are unable to reabsorb glucose efficiently. In this case, glucose spills over into the urine, even when blood glucose levels are within the normal range. This phenomenon is often seen in patients with renal tubular dysfunction.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely a distractor, as there is no direct link between the patient's symptoms and a diagnosis of diabetes mellitus. While diabetes can cause glycosuria, the patient's normal blood sugar levels make this option incorrect.
* **Option B:** This option is incorrect because the presence of glycosuria does not necessarily indicate an issue with pancreatic insulin production. The kidneys are responsible for glucose reabsorption, not the pancreas.
* **Option C:** This option is a plausible distractor, as renal impairment can indeed cause glycosuria. However, the patient's normal blood sugar levels and the absence of any other renal symptoms make this option less likely.

**Clinical Pearl / High-Yield Fact**
Glycosuria in the absence of hyperglycemia should prompt a search for underlying renal pathology, such as Fanconi syndrome or RTA. These conditions can cause renal tubular dysfunction, leading to glucose loss in the urine.

**Correct Answer:** C. Renal Tubular Acidosis (RTA)