Relationships among urinary protein-to-creatinine ratio, urine specific gravity, and bacteriuria in canine urine samples

BACKGROUND: Proteinuria is a marker of chronic kidney disease in dogs and a risk factor for increased morbidity and death. Predictive models using the results of readily available screening tests could foster early recognition. OBJECTIVE: To determine whether urine specific gravity (USG) and semiquantitative category of dipstick protein can be used to predict urinary protein-to-creatinine ratio (UP : C) and to examine the effect of urine culture results on UP : C in dogs. ANIMALS: Three hundred ninety-four dogs (482 visits) presented to a university Community Practice Clinic or Veterinary Teaching Hospital between January 2011 and November 2015. METHODS: Retrospective study. Medical records were searched to identify dogs for which urinalysis, UP : C measurement, and urine culture testing were performed during a single hospital visit. Urine specific gravity, UP : C, dipstick protein concentration, and findings of urine sediment analysis and urine culture were recorded. Regression or Spearman correlation analysis was used to test for relationships between UP : C and USG within dipstick categories and between UP : C and bacterial colony-forming units per milliliter, respectively. Cohen's kappa test was used to evaluate agreement between urine culture and UP : C testing. RESULTS: There were significant (P < .05) weak negative correlations (R2 range, 0.14-0.37) between UP : C and USG for all nonnegative urine protein dipstick categories. The presence of a positive urine culture did not agree with the presence of abnormal UP : C (κ = -0.06). CONCLUSIONS AND CLINICAL IMPORTANCE: Within dipstick protein categories, UP : C cannot be accurately predicted from USG. Repeating UP : C measurement after resolution of urinary tract infection is advisable.