A 68-year-old woman with type 2 diabetes is brought in obtunded after a week of reduced fluid intake during a diarrhoeal illness. Blood glucose is 940 mg/dL, effective serum osmolality 334 mOsm/kg, pH 7.38, bicarbonate 24 mEq/L, and serum beta-hydroxybutyrate mildly elevated. Which statement best characterises this presentation?

• A Severe metabolic acidosis with an anion gap above 20 mEq/L
• B Profound hyperglycaemia with hyperosmolality but minimal ketoacidosis ✓
• C Hyperglycaemia driven by complete insulin deficiency requiring fixed-rate insulin infusion as sole therapy
• D Renal glycosuria causing obligatory water loss with preserved sensorium

Explanation

Hyperosmolar hyperglycaemic state features extreme hyperglycaemia, effective osmolality above 320 mOsm/kg, marked dehydration, and altered consciousness with little or no ketoacidosis because residual portal insulin suppresses lipolysis. The normal pH and bicarbonate here exclude ketoacidotic coma. Management still includes insulin and fluids, but the defining laboratory signature is hyperosmolality without a significant anion gap acidosis.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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