Osmolal Gap Calculator
Calculate the osmolal gap — the difference between measured and calculated serum osmolality — to screen for unmeasured osmoles such as toxic alcohols.
When to use it
Use in unexplained high-anion-gap metabolic acidosis. An osmolal gap above 10 mOsm/kg raises concern for methanol or ethylene glycol ingestion and should prompt urgent toxicology input.
Formula
Calculated osmolality = 2 x sodium + glucose/18 + BUN/2.8 + ethanol/3.7. Osmolal gap = measured - calculated osmolality.
Category
Acid-Base & Electrolytes
References
- Kraut JA et al. Toxic alcohol ingestions: clinical features, diagnosis, and management. Clin J Am Soc Nephrol. 2008;3:208-25. PMID: 18045860
About NephroMind
This calculator is part of NephroMind, a free clinical decision-aid platform from the Arab Society of Nephrology and Renal Transplantation (ASNRT) — over 128 bedside nephrology calculators plus a renal drug-dosing database, coded by a practicing transplant nephrologist.