An obtunded man smells of alcohol. Labs: Na 140, Cl 105, HCO3 12 mEq/L, anion gap 23, glucose 95 mg/dL, measured osmolality 330 mOsm/kg, calculated osmolality 292 mOsm/kg. Urine microscopy shows envelope-shaped birefringent crystals. The most likely ingested toxin is:

• A Ethylene glycol ✓
• B Methanol
• C Isopropyl alcohol
• D Ethanol

Explanation

Ethylene glycol is metabolized to glycolate and oxalate, causing high anion gap metabolic acidosis, an elevated osmolal gap from unmeasured parent alcohol, and deposition of calcium oxalate dihydrate crystals that appear envelope shaped and birefringent. Methanol causes formate toxicity with visual symptoms but no oxalate crystals. Isopropyl alcohol causes ketosis without acidosis, and ethanol alone elevates the osmolal gap without raising the anion gap.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.