**Core Concept**
Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia, resulting from defects in insulin secretion, insulin action, or both. Life-threatening complications arise from the effects of hyperglycemia on various organs and systems.

**Why the Correct Answer is Right**
Life-threatening complications of diabetes mellitus include diabetic ketoacidosis (DKA), a metabolic state characterized by hyperglycemia, metabolic acidosis, and ketosis. DKA occurs when the body's insulin levels are insufficient to meet its needs, leading to the breakdown of fat for energy and the production of ketones. The pathophysiology involves impaired insulin secretion, increased glucagon levels, and decreased glucose uptake by cells.

**Why Each Wrong Option is Incorrect**
**Option A:**
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**Option B:**
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**Option C:**
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**Clinical Pearl / High-Yield Fact**
A key clinical feature of DKA is the presence of ketones in the urine, which can be detected using dipstick tests or measured using blood ketone meters.

**Correct Answer:**
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