An elderly man found drowsy at home has glucose 1150 mg/dL, sodium 152 mEq/L, pH 7.36, bicarbonate 20 mEq/L, and trace ketonuria. Which calculated value best confirms the diagnosis?
- A Effective serum osmolality above 320 mOsm/kg ✓
- B Corrected sodium above 160 mEq/L
- C Serum anion gap above 16 mEq/L
- D Urine ketone level of 4+
Correct answer: A. Effective serum osmolality above 320 mOsm/kg
Explanation
Hyperosmolar hyperglycaemic state is defined by marked hyperglycaemia (usually above 600 mg/dL), effective osmolality greater than 320 mOsm/kg, minimal ketosis, and near-normal pH. Effective osmolality equals 2 times sodium plus glucose divided by 18, which here is roughly 344 mOsm/kg. The anion gap is normal because ketoacidosis is absent, and corrected sodium reflects water deficit rather than defining this syndrome.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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