An unconscious young man found near an antifreeze container has Na+ 140 mEq/L, glucose 90 mg/dL, BUN 14 mg/dL, measured plasma osmolality 330 mOsm/kg. Which additional finding most strongly supports ethylene glycol ingestion?

• A Urine specific gravity of 1.010
• B Serum bicarbonate of 24 mEq/L
• C Serum calcium of 10.5 mg/dL
• D Urine microscopy showing envelope-shaped oxalate crystals ✓

Explanation

The calculated osmolality here is about 300 mOsm/kg against a measured value of 330, giving an elevated osmolar gap consistent with a toxic alcohol. Ethylene glycol is metabolised by alcohol dehydrogenase to glycolate and then oxalate; calcium oxalate crystals appear in urine as envelope-shaped or dumbbell forms, often with hypocalcaemia from crystal deposition with calcium. D normal bicarbonate would argue against the organic acidaemia that follows metabolism.

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

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