A 68-year-old man with type 2 diabetes is brought confused after a week of reduced fluid intake during a heat wave. Blood glucose is 850 mg/dL, effective serum osmolality is 335 mOsm/kg, pH is 7.36, bicarbonate is 22 mEq/L, and serum ketones are trace. Which feature most reliably separates his condition from diabetic ketoacidosis?
- A Degree of hyperglycaemia above 600 mg/dL
- B Effective serum osmolality above 320 mOsm/kg with absent significant ketoacidosis ✓
- C The presence of altered sensorium
- D Requirement for lower total insulin doses
Correct answer: B. Effective serum osmolality above 320 mOsm/kg with absent significant ketoacidosis
Explanation
Hyperosmolar hyperglycaemic state is defined by marked hyperglycaemia, an effective osmolality exceeding 320 mOsm/kg, profound dehydration, and minimal or absent ketosis with preserved acid-base status. Ketoacidosis is the discriminator: residual portal insulin in type 2 diabetes suppresses lipolysis enough to prevent ketoacid generation. Hyperglycaemia alone does not separate the syndromes since overlap occurs, and both conditions cause obtundation. Insulin requirements differ but are not diagnostic.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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