Influence of preanalytical factors on feline proteinuria

Background To date, little information is available about the effect of preanalytical factors on the urinary protein-to-creatinine (UPC) ratio in cats. Objectives We aimed to evaluate the effect of a commercially available cat litter, creatinine measurements at three different dilutions of urine, and different storage conditions on the UPC ratio in cats. Methods Feline urine specimens were prospectively collected. Twenty-two whole-urine specimens were placed uncovered and in contact with cat litter for 1 hour; 25 urine supernatants were diluted 1:10, 1:20, and 1:100 for creatinine measurements. The correlation, difference, agreement, and concordance in classifying specimens according to International Renal Interest Society staging were determined. Storage effects on UPC ratios were assessed in specimens stored for 6 hours at +20celcius (n = 20), 1 week at +4celcius (n = 20), and 3 months at -20celcius (n = 25). Specimens were also subjected to four freeze-thaw cycles (n = 20). Results were compared, and clinical significance was assessed by comparing each UPC ratio to the inter-assay range of the baseline value. Results Exposure to cat litter did not affect UPC ratios. A positive proportional bias was found in the 1:100 dilution compared with the 1:20 dilution; however, concordance was high for all comparisons. At +20, +4celcius, and after four repeated freeze-thaw cycles, UPC ratios were stable. Compared with baseline values, UPC ratios decreased (P < .01) after 8 and 12 weeks at -20celcius. However, all UPC ratios were within the inter-assay variability of the baseline value. Conclusions Exposure to cat litter did not affect UPC ratios, but further studies are necessary to evaluate other potential variables. The effects of the dilutions and storage conditions were clinically acceptable, although the 1:20 and 1:100 dilutions were not perfectly comparable.