Calculator: Serum osmolal gap (conventional units)*

Calculator: Serum osmolal gap (conventional units)^*

Input

Serum Na		mEq/L
Serum glucose
Serum BUN
Serum ethanol
Measured Osm
Ethanol osmolality factor^¶	4.6
	3.7

Results

Important: Inputs must be complete to perform calculation.


Calculated Osm
Osmolal gap

Decimal precision

Notes

The plasma osmolality is determined by the concentration of the different solutes in the plasma.
In healthy subjects, sodium salts (chloride and bicarbonate), glucose, and urea are the primary circulating solutes.
The calculated plasma osmolality is normally between 270 and 290 mOsm/kg H₂O, and the Osmolal gap is normally <10 mOsm/kg H₂O. You can calculate the Osmolal gap from the formulas depicted.
For more information on the serum osmolal gap and its use in clinical medicine, refer to appropriate UpToDate topic reviews and those that deal with ethanol, methanol, ethylene glycol, and isopropyl alcohol poisoning.
In this calculator, mcg is the abbreviation for micrograms.
BUN: blood urea nitrogen; Osm: osmolality.
* This calculator uses conventional units (also known as US units and gravimetric units) as the default for inputs. Do not use this calculator if you are using SI units (Système international d'unités); please refer instead to the SI units version of this calculator.
¶ When Serum ethanol is reported as mg/dL, the calculator allows the selection of 4.6 or 3.7 for the Ethanol osmolality factor, as there is some uncertainty about the best factor to use. The factor of 4.6 is based on ethanol's molar mass (46.07 g/mol), and 3.7 is based on empiric data that large quantities of ethanol (>100 mg/dL) can raise the osmolal gap more than would be expected because serum does not behave as an ideal fluid.

Equations used

Calculated_Osm = (Serum_Na * 2) + (Serum_glucose / 18) + (Serum_BUN / 2.8) + (Serum_ethanol / Ethanol osmolality factor^¶)

Osmolal_gap = Measured_Osm - Calculated_Osm

References

Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

Information on this page may not appear correctly if printed.

All information contained in and produced by the EBMcalc system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER.

Topic 13498 Version 15.0

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Calculator: Serum osmolal gap (conventional units)*