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Printed on 4/19/2026
For informational purposes only. This is not medical advice.
The osmolar gap is the difference between measured serum osmolality and calculated serum osmolality. An elevated gap can indicate unmeasured osmotically active substances and is often used in toxicology and critical care workups.
Formula: Osmolar Gap = Measured Osmolality - Calculated Osmolality.
A larger positive gap suggests unmeasured osmoles and should prompt focused toxicology and metabolic evaluation in the appropriate clinical scenario.
Use this tool when measured and calculated osmolality are both available and there is concern for toxic ingestion, unexplained acidosis, or altered mental status.
Gap thresholds vary by assay and institution. Osmolar gap is a screening clue, not a definitive diagnosis, and may be normal in late toxic alcohol presentations.
For related assessments, see Serum Osmolality, Anion Gap and ABG Interpreter.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
Calculate serum osmolality from sodium, glucose, and BUN. Normal range: 275–295 mOsm/kg. Osmolal gap >10 suggests toxic alcohol ingestion (methanol, ethylene glycol, isopropanol) or other unmeasured osmoles.
ClinicalCalculate anion gap and albumin-corrected anion gap to evaluate metabolic acidosis, narrow differential diagnosis, and monitor treatment response.
ClinicalInterpret arterial blood gas (ABG) results to identify acid-base disorders. Determines primary disorder and compensation status from pH, pCO₂, and HCO₃⁻.