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Updated: Aug 15, 2026
Microdialysis of Ethanol During Operant Ethanol Self-administration and Ethanol Determination by Gas Chromatography
Published on: September 5, 2012
Discrepancies in osmolal gaps and calculated alcohol concentrations
J D Osterloh1, T J Kelly, H Khayam-Bashi
1Department of Clinical Laboratory Medicine, University of California, San Francisco, USA.
Objectives:
To estimate unexplained osmolal gaps (UEOG) during ethanol ingestions after accounting for measured ethanol concentrations and to explore the causes of observed discrepancies. DESIGN AND SPECIMENS: A random convenience sample of serum specimens with a request to perform osmometry for the detection of alcohols was studied.
Main Outcome Measures:
Serum concentrations of sodium, glucose, urea nitrogen, ethanol, osmolality, and ethanol were measured by two analytic methods to determine calculated osmolalities and osmolal gaps using two commonly used formulas.
Results:
In 79 serum specimens submitted for osmometry, mean ethanol concentrations were 199 +/- 154 (SD) mg/dL; 15 specimens had no detectable ethanol. After regression of the calculated ethanol concentrations and the measured ethanol concentrations, the Dorwart and Chalmers formula showed a large constant bias of 45.217 +/- 6.414 (SE) mOsm/kg in predicting measured ethanol concentrations. The Smithline and Gardner formula was similarly as precise (r = .9786), but had a much smaller bias of -3.929 +/- 6.623 (SE) mOsm/kg. Actual mean differences between measured and calculated osmolalities (including ethanol osmols) gave an estimate of UEOG seen during ethanol ingestions. Using the less biased formula, the mean UEOG was 1.4 +/- 8.5 mOsm/kg, giving a 95% upper limit of the reference range of 18 mOsm/kg in this population with ethanol ingestions. Three significant outliers were identified and their UEOG could be explained by the presence of mannitol, isopropanol, or possibly a change in the assumed value for fractional water, normally a constant in these formulas for calculated osmolality. Other specific causes of osmolal gap and UEOG are discussed.
Conclusion:
The potential range of osmolal gaps seen during ethanol ingestions after accounting for ethanol is demonstrated to be greater than in previous studies, which have included a lower proportion of ethanol-intoxicated subjects in their study sample.
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