Calculate serum osmolality from sodium, glucose, urea and ethanol in mg/dL or mmol/L, and the osmolal gap from a measured value to screen for toxins.
About this tool
Calculated serum osmolality and osmolal gap.
How to use Serum Osmolality Calculator
- Choose conventional or SI units.
- Enter sodium, glucose and urea (BUN), plus ethanol if present.
- Add the measured osmolality to get the osmolal gap.
Worked example
Na 140, glucose 100 mg/dL and BUN 14 mg/dL give a calculated osmolality of 290.6 mOsm/kg.
What does a raised osmolal gap mean?
A gap above about 10 mOsm/kg suggests unmeasured osmoles such as methanol, ethylene glycol, isopropanol or mannitol.
Why include ethanol?
Ethanol is a common cause of a raised gap. Including it shows whether another toxin could explain what is left.
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