A 52-year-old woman with type 2 diabetes presents after 24 hours of vomiting. Her sodium is 127 mEq/L and glucose is 890 mg/dL. What is the likely diagnosis and its pathophysiology?

• A. Hyperosmolar Hyperglycemic State; hyperosmolarity
• B. Diabetic Ketoacidosis; metabolic acidosis
• C. Lactic acidosis; elevated lactate
• D. Hypoglycemia; low glucose

Answer: (A)

The key idea is that very high blood glucose with enough insulin to suppress significant ketoacidosis points to a hyperosmolar hyperglycemic state. In type 2 diabetes, profound hyperglycemia leads to osmotic diuresis, causing marked volume depletion and loss of electrolytes. The resulting elevated serum osmolality produces the hyperosmolar state, which drives the patient’s symptoms and mental status changes. Because there’s some endogenous insulin, lipolysis and ketogenesis are minimal, so metabolic acidosis is not a major feature, unlike in diabetic ketoacidosis. The apparent hyponatremia is mainly due to the osmotic shift from high glucose; correcting for glucose brings sodium closer to normal. Lactic acidosis or hypoglycemia would present differently.