Availability of a Digital Refractometer for Measuring Urine Specific Gravity in Dogs

Urine specific gravity (USG) is used clinically to assess urine concentration and is routinely evaluated with a refractometer. Several studies have compared optical and digital refractometers in assessing USG in dogs. However, these studies have shown conflicting results. Therefore, this study aimed to evaluate the clinical feasibility of a handheld digital refractometer (HDR) (Atago Pal-Usg Dog) for measuring USG.

Urine samples were collected from 100 dogs with various problems. The results of the HDR and the reference method, the optical handheld refractometer (OHR) (Atago URC-NE), were evaluated using dependent t-tests, Pearson correlation analysis, Passing-Bablok regression analysis, and Bland-Altman tests. Furthermore, the coefficient of variation (CV) and total analytical error (TAE) rates for the HDR were determined.

Although a statistically significant difference was determined between the mean USG measured with OHR and HDR, a positive correlation was found between the two refractometers. The Passing-Bablok regression analysis revealed no systematic or proportional bias between the two refractometers. The Bland-Altman test calculated the mean difference between the OHR and HDR measurements as -0.9 units, demonstrating that the USG measured with HDR could be 1.3 units greater or 3 units less than the OHR. When evaluating the CV, the reproducibility of the HDR was quite good, and for the TAE, this value fell within the desired limits for USG.

This study demonstrated that USG in dogs can be measured safely, easily, and quickly with the HDR and that the HDR is suitable for clinical use.