Comparison of measured ethanol and calculated ethanol using osmolal gap and osmolarity formulas

Abstract

Comparison of measured ethanol and calculated ethanol using osmolal gap and osmolarity formulasO smolality is the concentration of the osmoles of solute dissolved per kilogram of pure water (mOsmol/kg H 2 O), whereas osmolarity is the concentration of the osmoles of solute dissolved per liter of solution (mOsmol/L). These 2 terms can be used interchangeably, but osmolality is a more accurate term thermodynamically. Solution concentrations are expressed on the basis of weight, and therefore, it is independent of temperature and pressure. In contrast, solution concentrations are expressed on the basis of volume in osmolarity, and changes in volume can occur depending on the thermal expansion of the solution. As a result, osmolarity can lead to incorrect results in cases of hyperlipidemia or hyperproteinemia, or in the presence of osmotically active substances, such as alcohol or mannitol [1][2][3].The osmolal gap is the difference between measured osmolality and calculated osmolality. Normally, the osmolal gap is less than 10 mOsmol/kg H 2 O [4].A high concentration of alcohol, such as ethanol, methanol, isopropanol, ethylene glycol, or propylene glycol causes hyperosmolality and a high osmolal gap in proportion with the Objectives: Osmolality can be measured with an osmometer, and it can also be calculated using formulas that include the level of some osmotically active serum components. The difference between measured and calculated osmolality is referred to as the osmolal gap. The osmolal gap indirectly indicates the presence of osmotically active substances other than sodium, urea, and glucose. The aim of this study was to calculate the osmolal gap using 6 osmolarity formulas published in the literature and compare the measured ethanol concentrations with various ethanol calculation formulas that include the osmolal gap. Methods: Serum ethanol, glucose, potassium, sodium, and urea levels were measured. Serum osmolarity was calculated with 6 formulas and converted to osmolality (mOsmol/L-mOsmol/kg H 2 O) using a converting factor. The osmolal gap was determined using measured and calculated osmolality with 6 different formulas for each sample. The osmolal gap values were multiplied by the ethanol coefficient used to ascertain the effect of ethanol on serum osmolality in order to obtain the amount of ethanol in the samples. Results: A positive correlation was observed between the 24 calculated ethanol levels and measured ethanol levels. No statistically significant difference was seen between the measured ethanol levels and 1 of the formulas, but there were systematic differences between them. Conclusion: Estimating the ethanol concentration with this type of approach is particularly inappropriate in forensic cases. The osmolal gap should only be used for screening toxic alcohols as an adjunct to clinical decision-making in emergency departments when ethanol cannot be measured, as in a case of alcohol intoxication.