Comparison of methods for calculating serum osmolality: multivariate linear regression analysis

Abstract

AbstractBackground: There are several methods for calculating serum osmolality, and their accordance with measured osmolality is the subject of controversy.Methods: The concentrations of sodium, potassium, glucose, blood urea nitrogen (BUN) and osmolalities of 210 serum samples were measured. Two empirical equations were deduced for the calculation of serum osmolality by regression analysis of the data. To choose the best equation, chemical concentrations were also used to calculate osmolalities according to our formulas and 16 different equations were taken from the literature and compared with the measured osmolalities. Correlation and linear regression analyses were performed using Excel and SPSS software.Results: Multiple linear regression analysis showed that serum concentrations of sodium (β=0.778, p≤0.000), BUN (β=0.315, p≤0.000), glucose (β=0.0.089, p≤0.007) and potassium (β=0.109, p≤0.008) are strong predictors of serum osmolality. The data were also analyzed by manual linear regression to yield the equations: osmolality=1.897[NaConclusions: Our data suggest use of the Worthley et al. formula Osm=2[Na