Reliability of 3 Urine Specific Gravity Meters for Measuring Brix and Urine Solutions at Different Temperatures.

HYDRATION; STATISTICS; CONFIDENCE intervals; SPECIFIC gravity; RESEARCH methodology; REFRACTIVE index; QUANTITATIVE research; MANN Whitney U Test; URINE collection & preservation; DESCRIPTIVE statistics; URINALYSIS; DATA analysis

Context: Urine specific gravity (USG) should be measured at room temperature (208°C), but the temperature of the sample is not always considered. Objective: To evaluate the effect of sample temperature on the measurement accuracy of a digital refractometer (DIG), manual optical refractometer (MAN), and hydrometer (HYD). Design: Descriptive laboratory study. Main Outcome Measure(s): Urine specific gravity. Results: Experiment 1 (24 Brix (0Bx) samples) showed that measurements via the DIG and MAN did not differ from the reference, but HYD provided lower or inconsistent values compared with 0Bx and was highly correlated with 0Bx solutions (r, . = 0.89). The overall diagnostic ability of elevated USG cutoff values (1.020, 1.025, 1.030) was high for all tools (area under the curve .0.92). Misclassification of samples increased from 0 to 2 at 1.020 to 1 to 3 samples at cutoffs of 1.025 and 1.030 USG. Bland-Altman analysis showed that the DIG 58°C underreported slightly without reporting bias (r = 0.344, P = .13); all other plots for the DIG, MAN, and HYD showed considerably larger underreporting at higher concentrations (r = 0.21 to 0.97 with P ..02) at all temperatures. The outcomes of experiment 2 (33 fresh urine samples) using DIG 208°C as the standard demonstrated only negligible differences between the DIG and MAN at all temperatures but larger differences using the HYD. Conclusions: All tools showed reporting bias compared with the 8Bx solutions, which can affect the classification of low and high urine concentration at higher USG cutoff values, especially with a sample temperature of 378°C. [ABSTRACT FROM AUTHOR]

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