**Core Concept**
Ketosis is a metabolic state characterized by the production of ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) due to the breakdown of fatty acids for energy. This occurs when the body's glucose levels are low, such as during prolonged fasting, starvation, or uncontrolled diabetes mellitus.

**Why the Correct Answer is Right**
In diabetes mellitus, ketosis occurs when the body's insulin levels are low, leading to increased glucagon levels. Glucagon stimulates the breakdown of glycogen and fat stores, resulting in the production of ketone bodies. This process is also facilitated by the activation of hormone-sensitive lipase, which releases free fatty acids from adipose tissue. The kidneys then excrete excess ketone bodies in the urine, leading to ketonuria.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a characteristic of ketosis in diabetes mellitus. While elevated blood glucose levels are a hallmark of diabetes, they are not a direct feature of ketosis.
* **Option B:** This option is incorrect because ketosis is not typically associated with an increase in blood glucose levels. In fact, ketosis often occurs in the context of low glucose levels, such as during fasting or starvation.
* **Option C:** This option is not a feature of ketosis in diabetes mellitus. While an increase in urine glucose levels may be seen in diabetes, it is not a direct consequence of ketosis.

**Clinical Pearl / High-Yield Fact**
A key aspect of managing diabetic ketoacidosis (DKA) is to replace fluids and electrolytes lost through excessive urination. This is critical in preventing complications such as hypokalemia and hypophosphatemia.

**Correct Answer:** D.