Comparison of electrical conductivity and freezing point methods for urine osmolality measurement and the influence of urinary biochemical parameters

Abstract Objectives To evaluate the analytical performance of the Sysmex UF-5000 (electrical conductivity) and OSMOMAT 3000 basic (freezing point) devices for urine osmolality measurement and to investigate the influence of urinary biochemical parameters on the trueness of conductivity-based measurements. Methods A total of 210 urine samples were collected from outpatients and analyzed for osmolality using both devices. Urinary concentrations of creatinine, urea, glucose, calcium, potassium, sodium, chloride, total protein, and microalbumin were measured. Precision, trueness, method comparison, and the impact of biochemical parameters were assessed according to CLSI EP05-A3 and EP09-A3 guidelines. Statistical analyses included Spearman’s correlation, Passing–Bablok regression, Bland–Altman plots, and multiple regression analyses to identify predictors of osmolality. Results Both methods demonstrated high repeatability, with total %CV values below 14.2 %. Trueness (%bias) was 7.5 % for Sysmex UF-5000 and 7.1 % for OSMOMAT 3000. No significant difference was observed between median osmolality values (563.5 vs. 541 mOsm/kg, p=0.348). Correlation between devices was strong (Spearman’s rho (ρ)=0.93, p<0.01) and regression analyses indicated that sodium, potassium, calcium, and creatinine significantly influenced osmolality results for both devices. Glucose, urea, and microalbumin had negligible effects on electrical conductivity-based measurements. Conclusions Electrical conductivity may serve as a practical approach for estimating urine osmolality in comparison with the freezing point method, while ionic composition and pH-dependent charged species can still influence particular samples.