Toxic alcohols

Toxic Alcohols

Substance	Osmolar gap	Metabolic acidosis	Anion gap	Ketones	Ca Oxalate crystals	Reduced vision	Management
Ethanol	+	+/- (if ketoacidosis)	+/- (if ketoacidosis)	+/-	-	-	Mainly supportive
Ethylene glycol	+ (early)*	+	+	-	+	-	Fomepizole, Thiamine, Pyridoxine, +/- Dialysis
Methanol	+ (early)*	+	+	-	-	+	Fomepizole or ethanol, Folinic acid/Folic acid, +/- Dialysis
Isopropyl alcohol	+	-	-	+ (acetonemia without acidosis)	-	-	Mainly supportive, +/- Dialysis if severe
Propylene glycol	+	+	+ (lactic acidosis)	-	-	-	D/C offending agent (e.g. IV lorazepam/diazepam), supportive, +/- Dialysis

Osmolar gap → Anion gap transition: For all toxic alcohols, the osmolar gap is elevated early (parent compound present) and decreases over time as the alcohol is metabolized into organic acid metabolites, which then produce an anion gap metabolic acidosis. A normal osmolar gap does NOT exclude toxic alcohol ingestion if presentation is delayed.

Isopropyl alcohol: The only toxic alcohol that causes ketosis without metabolic acidosis (metabolized to acetone, not an organic acid)

Ethylene glycol: Ca oxalate crystals in urine + anion gap metabolic acidosis + renal failure

Methanol: Visual disturbances (blurred vision, "snowfield" vision, blindness) + anion gap metabolic acidosis + optic disc hyperemia on fundoscopy

Serum Osmolal Gap
Parameter	Value
Measured Serum Osmolality (mOsm/kg)
Sodium (Na⁺) mEq/L
BUN (mg/dL)
Glucose (mg/dL)
Results
Calculated Osmolality	mOsm/kg
Osmolal Gap	mOsm/kg

Interpretation
<10	Normal — No significant unmeasured osmoles detected.
>10	Elevated — Consider toxic alcohol ingestion: methanol, ethylene glycol, isopropanol, or other unmeasured osmoles (ethanol, mannitol, contrast dye).

References
Smithline N, Gardner KD Jr. Gaps—anionic and osmolal. JAMA. 1976;236(14):1594-1597. PMID 989116. Kraut JA, Xing SX. Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis. Am J Kidney Dis. 2011;58(3):480-484. PMID 21794966. Formula: Calculated Osm = 2(Na) + BUN/2.8 + Glucose/18. Gap = Measured − Calculated.

Interpretation
275–295	Normal serum osmolality.
Osmolal gap = Measured Osm – Calculated Osm. Gap >10 suggests unmeasured osmoles (toxic alcohols, mannitol, etc.).

References
Formula: Osm = 2×Na + BUN/2.8 + Glucose/18 Purssell RA, et al. Derivation and validation of a formula to calculate the contribution of ethanol to the osmolal gap. Ann Emerg Med. 2001;38(6):653-659. PMID 11719745.

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