Serum osmolal gap and ethanol concentration: a simple and accurate formula

Area of Science:

• Clinical Chemistry
• Toxicology
• Biophysics

Background:

• Serum osmolality is used to estimate ethanol concentration.
• Previous formulas assumed ideal solutions, which may not be accurate for ethanol in serum.

Purpose of the Study:

• To re-evaluate the estimation of serum ethanol concentration via serum osmolality.
• To develop and validate a new formula for calculating serum ethanol based on osmolal gap.

Main Methods:

• Validated a formula for serum osmolality in 193 non-ethanol-ingesting patients.
• Correlated osmolal gap with measured serum ethanol in 37 samples from 35 patients.
• Validated the new formula in 32 additional serum samples.

Main Results:

• The mean osmolal gap in non-ethanol patients was 1.5 mOsm/Kg +/- 5.3 mOsm/Kg.
• A high correlation (r = 0.994) was found between osmolal gap and serum ethanol.
• The derived formula, Ethanol = 0.83 X osmolal gap, accurately predicted serum ethanol (r = 0.988).

Conclusions:

• The factor 0.83 indicates non-ideal behavior of ethanol in serum.
• The proposed formula provides an accurate, experimentally derived method for estimating serum ethanol.
• This new formula supersedes previous methods that relied on unverified assumptions of ideality.