A New Equation in the Calculation of Osmolality Before and After Hemodialysis Session

Objective: In this study, in hemodialysis patients, we aimed to compare the osmolality values calculated by the equations that are frequently used in the literature and the values measured on the osmometer device, and also to present new equations that are obtained from regression analysis for calculating serum osmolality. In addition, in the evaluation of hemodialysis adequacy of patients, we aimed to evaluate the effectiveness of our equations by comparing the osmolality values calculated with our equations and the measured osmolality values. Methods: New equations for pre- and posthemodialysis were obtained by linear regression analysis from the pre- and posthemodialysis examination parameters that were analyzed for hemodialysis adequacy assessment: For prehemodialysis serum osmolality = 1.37 × ([Na+ ] + [K+ ]) + 1.1 × BUN+Glucose + 85 For posthemodialysis serum osmolality = 1.2 × ([Na+ ] + [K+ ]) +BUN+Glucose + 110 Comparison and correlation of measured and calculated osmolality values were carried out with statistical tests, separately for before and after hemodialysis. Results: Considering the high correlation strength, low osmolal gap mean and standard deviation, and the lack of significant difference between the measured and calculated osmolality in the selection of the equation with the best results, it is seen that the best results were obtained using our equations and the “2 × ([Na+ ] + [K+ ]) +Glucose +BUN” equation. Conclusion: We suggest using our equations and the equation “2 × ([Na+ ] + [K+ ]) +Glucose +BUN,” which are evaluated as better performing equations according to the results of our study.