Answer
Substances That Can Cause an Osmolar Gap >10 mOsm/kg
An elevated osmolar gap—defined as the difference between measured and calculated serum osmolality—can indicate the presence of unmeasured osmotically active substances in the blood. A gap >10 mOsm/kg is often clinically significant and may signal toxic alcohol ingestion.
🔬 Three Key Substances That Elevate the Osmolar Gap
1. Methanol
Methanol is a toxic alcohol commonly found in industrial solvents, antifreeze, and contaminated alcoholic beverages. Once ingested, it is metabolized to formaldehyde and then to formic acid, which causes metabolic acidosis and optic nerve damage.
- Clinical features: Visual disturbances, nausea, confusion, seizures
- Osmolar gap: Elevated due to unmetabolized methanol
2. Ethylene Glycol
Ethylene glycol is a component of antifreeze and deicing agents. It is metabolized to glycolic acid and oxalic acid, which cause profound acidosis, renal failure, and neurological damage.
- Clinical features: Flank pain, hematuria, confusion, metabolic acidosis
- Osmolar gap: Increased in early stages due to unmetabolized ethylene glycol
3. Isopropanol
Isopropanol (isopropyl alcohol) is found in rubbing alcohol and disinfectants. It is metabolized to acetone, which does not cause acidosis but contributes to CNS depression and ketonemia.
- Clinical features: CNS depression, hypotension, fruity breath odor
- Osmolar gap: Elevated without accompanying acidosis
📌 Summary
Elevated osmolar gaps are red flags for ingestion of toxic alcohols. Prompt recognition of substances like methanol, ethylene glycol, and isopropanol is critical for timely management and prevention of life-threatening complications.