Effect of Sampling Method and Storage Conditions on Albumin, Retinol-Binding Protein, And N-Acetyl-β-D-Glucosaminidase Concentrations in Canine Urine Samples

Abstract

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-b-D-glucosaminidase (uNAG) concentrations in cystocentesis and voided samples and to investigate concentration changes after storage at 220uC and at 280uC. Effects of a protease inhibitor were also assessed in samples stored at 280uC 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 220uC, 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 280uC, 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.

Escherichia coli Pyometra Induces Transient Glomerular and Tubular Dysfunction in Dogs

“…Furthermore, the combination of hematuria, bacteriuria, and pyuria affected urinary albumin concentrations in a larger amount of samples 41 . Recent work from our group suggested no effect of ex vivo addition of white blood cells, red blood cells, and bacteria to urine samples regarding uAlb/Cr, uRBP/Cr, and uNAG/Cr 42 . However, the latter is not equivalent to tissue infection in vivo.…”

“…41 Recent work from our group suggested no effect of ex vivo addition of white blood cells, red blood cells, and bacteria to urine samples regarding uAlb/Cr, uRBP/Cr, and uNAG/Cr. 42 However, the latter is not equivalent to tissue infection in vivo. Although the urinary biomarker concentrations of the mentioned 6 dogs with pyometra did not significantly differ from the median value of the remainder of the pyometra group, the effect of pyuria, hematuria, and bacteriuria on the urinary biomarkers needs to be addressed in future research.…”

Evaluation of Kidney Injury in Dogs with Pyometra Based on Proteinuria, Renal Histomorphology, and Urinary Biomarkers

“…Although severe renal lesions were present in 1 of the 3 dogs with UTI and UPC>0.5, the increased UPC of the other 2 dogs could be the result of UTI. In addition, the effect of UTI on urinary biomarker concentrations needs to be further examined in future studies 23 . Although the presence of upper UTI is less likely because of the absence of ultrasonographic findings typical for pyelonephritis, 24 it cannot be definitively excluded in the dogs with UTI.…”

Renal biomarkers in domestic species

“…A canine‐specific RBP ELISA was recently marketed (ICL); however, validation and use of this kit has not yet been published. Retinol‐binding protein concentration is similar in cystocentesis vs voided urine samples from clinically healthy dogs . Retinol‐binding protein appears to be relatively stable in canine urine samples when frozen, ideally at −80°C .…”