Performance Evaluation of Urine Osmolality Measurement on Sysmex UF-5000 and the Effect of Molecules and Particles in Urine

Background: Urine osmolality determines the concentration ability of the kidney. Therefore, it is used to assess the body's hydration status, electrolyte levels, and acid-base disturbances. We aimed to evaluate the analytical perfor-mance of osmolality measurement of the Sysmex UF-5000 (UF-5000), to examine the effect of different molecules and particles in the urine on the osmolality measurement. Methods: Complete urinalysis and conductivity-based osmolality analysis with UF-5000 and osmolality analysis with Advanced (R) Model 3320 Micro-Osmometer (AI-3320) by freezing point reduction method were performed in the urine samples. Samples were grouped as negative, glucosuria, proteinuria, hematuria, pyuria, crystalluria, and urobilinogen.Results: Total impressions were calculated as < 5% and accuracy values were < 1.66% in both analyzers. The re-gression equation was found to be y =-12.54 + 0.956x and the relative difference between the analyzers was 8.7% in 586 samples. When patients with Glucose > 2+ were excluded the regression equation of 507 samples was found as y = 5.10 + 0.948x and the relative difference was 4.6%. The percentages of samples with a difference greater than the allowable difference were 18.8%, 11.6%, 35.9%, 13.7%, 18.7%, and < 12.2% in all samples, all samples without glucosuria > 2+, glucosuria, glucosuria < 3+, proteinuria, and other subgroups, respectively. Conclusions: Considering the good accessibility of the automated routine complete urine analyzer, UF-5000 can be considered to determine whether urine osmolality is within reference or should be measured by methods based on colligative properties. Thus, referral of patients to a clinic that uses the colligative measurement method may be used more effectively.(Clin. Lab. 2023;69:543-552. DOI: 10.7754/Clin.Lab.2022.220536)