• Evaluation of suspected toxic alcohol ingestion (Methanol, Ethylene Glycol, Diethylene Glycol, Propylene Glycol).
• Workup of High Anion Gap Metabolic Acidosis (HAGMA) with an unknown etiology.
• Suspicion of "Osmotic Diuretics" in circulation (e.g., Mannitol, Sorbitol, Glycerol).
• Screening for pseudohyponatremia (extreme hyperlipidemia or hyperproteinemia).

If specific levels are unknown, the gap can provide a rough estimate of concentration. Divisors for calculation: Ethanol (4.6), Methanol (3.2), Ethylene Glycol (6.2), Isopropanol (6.0).

The Osmolality Gap is highest shortly after ingestion (the parent alcohol is the osmole). As the alcohol is metabolized into acidic metabolites (e.g., formic acid, glycolic acid), the Osmolality Gap falls while the Anion Gap rises.

• Measured osmolality MUST be performed using Freezing Point Depression. Vapor pressure osmometry will miss volatile substances like ethanol or methanol.
• A "normal" gap (<10) does NOT rule out toxicity in a late-presenting patient where the parent alcohol has already been metabolized.
• Isopropanol increases the Osmolality Gap but does NOT typically cause a HAGMA (it is metabolized to acetone, a ketone but not an acid).

• Chronic kidney disease (accumulation of endogenous osmoles like trimethylamine N-oxide).
• Ketoacidosis or Lactic Acidosis (can cause modest increases up to 15–20).
• Hypermagnesemia.

• Assess for metabolic acidosis (pH < 7.3) and elevated Anion Gap (> 12).
• Obtain specific toxic alcohol levels (gold standard, though often delayed).
• Screen for end-organ damage: Fundoscopy (methanol/retinal edema) and Wood’s lamp of urine (ethylene glycol/fluorescein).
• Initiate Fomepizole or Ethanol infusion if the gap is > 20 and ingestion is suspected.
• Consult Nephrology for emergent hemodialysis if pH < 7.1, renal failure, or visual changes are present.

A giant in medical toxicology based at NYU/Bellevue. His work standardized the use of the Osmolality Gap as a standard-of-care screening tool in Emergency Departments globally.

The 2Na + Gluc/18 + BUN/2.8 formula was developed to simplify the assessment of plasma tonicity. The "gap" concept arose as a way to quantify "unaccounted-for" solutes, originally applied to differentiate etiologies of hyponatremia before being adapted for toxicology.