**Core Concept**
Glucose plasma clearance is a measure of the rate at which glucose is removed from the bloodstream by the liver and kidneys. In diabetes mellitus, glucose metabolism is impaired due to insulin resistance or deficiency, leading to altered glucose handling by the body.

**Why the Correct Answer is Right**
In diabetic patients, the plasma clearance of glucose is decreased due to impaired insulin-mediated glucose uptake by peripheral tissues. Insulin normally facilitates the translocation of glucose transporter type 4 (GLUT4) to the cell surface, allowing glucose to enter the cell. In diabetes, this process is impaired, reducing glucose uptake by muscle and fat cells. As a result, glucose remains in the bloodstream, leading to hyperglycemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately reflect the changes in glucose clearance in diabetes mellitus.
* **Option B:** This option is incorrect because it implies an increase in glucose clearance, which is not observed in diabetic patients.
* **Option C:** This option is incorrect because it suggests a role for glucagon in glucose clearance, which is not directly relevant to the impaired glucose handling seen in diabetes.

**Clinical Pearl / High-Yield Fact**
In diabetic patients, impaired glucose clearance can lead to hyperglycemia, which can cause a range of complications, including microvascular damage, neuropathy, and increased risk of infections. Monitoring glucose levels and adjusting treatment as needed is crucial to prevent these complications.

**Correct Answer:** B. Decreased