**Core Concept**
Hypersmolar hyperglycemic non-ketotic coma (HHNK) is a life-threatening condition characterized by severe hyperglycemia, dehydration, and altered mental status, without the presence of ketosis. It is often seen in elderly patients with type 2 diabetes.

**Why the Correct Answer is Right**
The blood glucose level in HHNK is typically extremely high, often exceeding 600 mg/dL. This is due to the body's relative inability to produce insulin, combined with an increased glucose load from the diet, and possibly from an underlying infection or other stressor. The kidneys are unable to effectively reabsorb glucose, leading to an osmotic diuresis and subsequent dehydration. The brain's attempt to compensate for the hyperosmolar state leads to the production of an excessive amount of urine, further exacerbating the dehydration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely too low; HHNK typically occurs in the setting of severe hyperglycemia, not mild hyperglycemia.
**Option B:** This option is also incorrect; while ketosis is a hallmark of diabetic ketoacidosis, HHNK is characterized by the absence of ketosis.
**Option C:** This option is not specific enough; HHNK can occur at various glucose levels, but typically exceeds 600 mg/dL.

**Clinical Pearl / High-Yield Fact**
HHNK is often referred to as "diabetic coma" because of its similarity to the presentation of diabetic ketoacidosis, but it is a distinct clinical entity with a different underlying pathophysiology.

**Correct Answer:** C. 600 mg/dL