Effect of sampling method and storage conditions on albumin, retinol-binding protein, and N-acetyl-β-D-glucosaminidase concentrations in canine urine samples

Abstract

Urinary markers for renal dysfunction are gaining interest, but effects of sampling method, storage conditions, and urinary tract inflammation or infection on these markers are unclear. Therefore, the objectives of the current study were to determine the difference in urinary albumin (uALB), urinary retinolbinding protein (uRBP), and urinary N-acetyl-β-D-glucosaminidase (uNAG) concentrations in cystocentesis and voided samples and to investigate concentration changes after storage at -20°C and at -80°C. Effects of a protease inhibitor were also assessed in samples stored at -80°C for 12 months. In a pilot experiment, influence of in vitro hematuria, pyuria, and bacteriuria on the urinary markers was evaluated. A mixed model was used to calculate mean differences and 95% confidence intervals. Urinary ALB, uNAG, and uRBP concentrations were similar in voided and cystocentesis samples. After storage for 4 months at -20°C, uALB concentration was not affected, and uRBP concentration showed a mild and clinically irrelevant decrease, whereas uNAG activity was significantly lower compared with fresh samples. After storage for 12 months at -80°C, uALB and uRBP concentrations did not differ from fresh samples, but uNAG activity was severely decreased. Protease inhibitor addition did not preserve uNAG activity. Experimental hematuria, pyuria, and bacteriuria did not seem to affect urinary markers, although further research is needed.