Osmolality Gap Calculator

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The osmolality gap (OG) is an indication of unmeasured solute in the blood.
It is determined by the measured osmolality (MO) minus the calculated osmolality (CO).

Where:

Here's an easy way to calculate it.

Plasma sodium concentration: mmol/L
Plasma glucose: mg/dL
Plasma urea: mg/dL
Measured Osmolality, plasma: mOsm/kg H2O

 Osmolality Gap: mOsm/kg H2O


If the above Osmolality Gap is elevated, the amount of one of these candidate substances that may explain the elevation will be calculated by checking an option below:
ETOH, mg/dL see ref.3
Ethylene Glycol, mg/dL
Methyl Alcohol, mg/dL
Isopropyl Alcohol, mg/dL

References

  1. Glasser, L., et al. Serum Osmolality and its applicability to drug overdose. Am. J. Clin. Path. 60:695, 1973
  2. Jacobsen, D., et al. {series of three articles dealing with methanol and ethylene glycol overdose and use of anion gap and osmolality gap in diagnosis}. Acta. Med. Scand. 212:1-20, 1982.
  3. Khajuria, A., and Krahn, J. Osmolality revisited - deriving and validating the best formula for osmolality. Clin. Biochem. 38: 514-519, 2005.