title: Evaluation of factors that affect analytic variability of urine protein-to-creatinine ratio determination in dogs.
abstract: OBJECTIVE
  To determine whether preanalytic and analytic factors affect evaluation of the urinary protein-to-creatinine (UPC) ratio in dogs.
  
  
  METHODS
  50 canine urine samples.
  
  
  METHODS
  The UPC ratio was measured to assess the intra-assay imprecision (20 measurements within a single session), the influence of predilution (1:10, 1:20, and 1:100) for urine creatinine concentration measurement, and the effect of storage at room temperature (approx 20°C), 4°C, and -20°C.
  
  
  RESULTS
  The coefficient of variation at room temperature determined with the 1:20 predilution was < 10.0%, with the highest coefficients of variation found in samples with a low protein concentration or low urine specific gravity. This variability could result in misclassification of samples with UPC ratios close to the thresholds defined by the International Renal Interest Society to classify dogs as nonproteinuric (0.2), borderline proteinuric (0.21 to 0.50), or proteinuric (> 0.51). A proportional bias was found in samples prediluted 1:10, compared with samples prediluted 1:20 or 1:100. At room temperature, the UPC ratio did not significantly increase after 2 and 4 hours. After 12 hours at room temperature and at 4°C, the UPC ratio significantly increased. The UPC ratio did not significantly change during 3 months of storage at -20°C.
  
  
  CONCLUSIONS
  The intra-assay precision of the UPC ratio was sufficiently low to avoid misclassification of samples, except for values close to 0.2 or 0.5. The optimal predilution ratio for urine creatinine concentration measurement was 1:20. A 1:100 predilution is recommended in samples with a urine specific gravity > 1.030. The UPC ratio must be measured as soon as samples are collected. Alternatively, samples should be immediately frozen to increase their stability and minimize the risk of misclassification of proteinuria.
authors.affiliation: Department of Veterinary Pathology, Hygiene and Public Health, University of Milano, 20133 Milan, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Rossi
authors.forename: Luca
authors.initials: L
authors.lastname: Giori
authors.forename: Simona
authors.initials: S
authors.lastname: Campagnola
authors.forename: Andrea
authors.initials: A
authors.lastname: Zatelli
authors.forename: Eric
authors.initials: E
authors.lastname: Zini
authors.forename: Saverio
authors.initials: S
authors.lastname: Paltrinieri
mesh_terms: D000818:Animals; D003404:Creatinine / Q000652:urine*; D004283:Dog Diseases / Q000175:diagnosis* / Q000652:urine*; D004285:Dogs; D007674:Kidney Diseases / Q000175:diagnosis / Q000652:urine / Q000662:veterinary*; D011507:Proteinuria / Q000175:diagnosis / Q000662:veterinary*; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000379:methods / Q000662:veterinary*; D018709:Statistics, Nonparametric; D013696:Temperature
chemical_list: D003404:Creatinine