title: Comparison of a digital and an optical analogue hand-held refractometer for the measurement of canine urine specific gravity.
abstract: Urine specific gravity (USG) is used clinically as a measure of urine concentration, and is routinely assessed by refractometry. A comparison between optical analogue and digital refractometers for evaluation of canine urine has not been reported. The aim of this study was to compare a digital and an optical analogue hand-held refractometer for the measurement of canine USG, and to assess correlation with urine osmolality. Prospective study. Free-catch urine samples were collected from 285 hospitalised adult dogs, and paired USG readings were obtained with a digital and an optical analogue refractometer. In 50 dogs, urine osmolality was also measured using a freezing point depression osmometer. There was a small but statistically significant difference between the two refractometers (P<0.001), with the optical analogue refractometer reading higher than the digital refractometer (mean difference 0.0006, sd 0.0012). Paired refractometer measurements varied by <0.002 in 91.5 per cent of cases. The optical analogue and digital refractometer readings showed excellent correlation with osmolality (r=0.980 and r=0.977, respectively, P<0.001 in both cases). Despite statistical significance, the difference between the two refractometers is unlikely to be clinically significant. Both instruments provide an accurate assessment of USG in dogs.
authors.affiliation: Royal (Dick) School of Veterinary Studies and the Roslin Institute, Division of Clinical Veterinary Sciences, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian EH25 9RG, UK. jparis@staffmail.ed.ac.uk
authors.forename: J K
authors.initials: JK
authors.lastname: Paris
authors.forename: A D
authors.initials: AD
authors.lastname: Bennett
authors.forename: S J
authors.initials: SJ
authors.lastname: Dodkin
authors.forename: D A
authors.initials: DA
authors.lastname: Gunn-Moore
mesh_terms: D000818:Animals; D004285:Dogs / Q000652:urine*; D009994:Osmolar Concentration; D012031:Refractometry / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D015203:Reproducibility of Results; D013046:Specific Gravity; D016482:Urinalysis / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D014556:Urine / Q000737:chemistry*