Agreement of urine specific gravity measurements between manual and digital refractometers

Abstract

Context: Urine specific gravity (Usg), measured by a handheld manual refractometer (MAN), has been recognized as a valid and practical means of assessing hydration status. Newer, digital refractometers are faster and more user friendly but have not been validated against the traditional MAN. Objective: To compare the reliability and validity of 2 digital refractometer models and a MAN. Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: Sample of convenience was recruited from the local university and surrounding community (n = 82). Intervention(s): Participants provided multiple urine samples (n = 124) over a 5-month period under various hydration conditions. Main Outcome Measure(s): Urine specific gravity was compared among a MAN, a digital refractometer requiring the prism to be dipped (DIP) into a urine sample, and a digital refractometer that requires urine to be pipetted (PIP) onto its prism for analysis. Results: The MAN measurements were strongly correlated with the DIP (r = 0.99, P