## Differentiation of Methanol vs. Ethylene Glycol Poisoning ### Why Direct Toxic Alcohol Measurement is Best **Key Point:** Gas chromatography or HPLC measurement of serum or urine methanol and ethylene glycol is the only definitive way to identify which toxic alcohol was ingested and guide specific antidote therapy. **High-Yield:** Both methanol and ethylene glycol cause wide anion gap metabolic acidosis and elevated osmolar gap, making clinical and biochemical differentiation difficult without direct measurement. ### Comparison of Methanol vs. Ethylene Glycol | Feature | Methanol | Ethylene Glycol | |---|---|---| | **Primary toxicity** | Optic nerve (blindness) | Kidney (acute tubular necrosis) | | **Urine findings** | Clear, no crystals | Calcium oxalate monohydrate crystals (early) | | **CNS signs** | Visual disturbances, optic disc hyperemia | Seizures, altered mental status | | **Renal involvement** | Minimal | Severe (acute kidney injury) | | **Specific antidote** | Fomepizole or ethanol | Fomepizole or ethanol (same) | ### Why Other Tests Are Insufficient **Clinical Pearl:** Urine calcium oxalate crystals suggest ethylene glycol but are not always present and are not specific. Serum creatinine elevation indicates renal damage (more common in ethylene glycol) but is a late finding. Repeat ABG does not differentiate the toxins. **Mnemonic:** **GC-MS** = **G**as **C**hromatography–**M**ass **S**pectrometry (or simple GC/HPLC) for direct toxic alcohol identification. ### Clinical Urgency Once osmolar gap and anion gap metabolic acidosis are confirmed, direct measurement of methanol and ethylene glycol should be sent immediately. Do not wait for clinical differentiation (visual symptoms for methanol, renal failure for ethylene glycol) — both require urgent antidote therapy (fomepizole 15 mg/kg IV loading dose). [cite:Park 26e Ch 13]
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