A 61-year-old man presented with an increased anion-gap metabolic acidosis, an increased serum osmolal gap, and a negative result in an alcohol screen. Gas chromatography revealed an increased ethylene glycol (EG) 2 concentration (22 mg/dL) and a propylene glycol (PG) result that was below the lower limit of quantification (Ͻ5 mg/dL) (Fig. 1A) . The patient was treated with hemodialysis, followed by phenytoin and a high-dose lorazepam infusion for a witnessed seizure. By 13 h, the EG

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... on had fallen below the lower limit of quantification (Ͻ5 mg/dL); however, a peak identified as PG was observed, corresponding to a concentration of 27 mg/dL (Fig. 1B) . QUESTIONS 1. What are the common causes of EG or PG poisoning? 2. What could cause a positive EG result and then a positive PG result in this patient? 3. What is the difference in toxicity between EG and PG? The answers are on the next page.