Influence of preanalytical factors on feline proteinuria

Abstract

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 wholeurine 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 +20℃ (n = 20), 1 week at +4℃ (n = 20), and 3 months at −20℃ (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, +4℃, 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 −20℃. 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.

The effect of non‐absorbent hydrophobic sand litter on the urine protein‐to‐creatinine ratio in feline urine

“…Collection at home would have significant cost benefits to owners and might also reduce stress for feline patients. Our findings are in agreement with a recent study by Giraldi and others, which demonstrated that urine exposure to non‐absorbent plastic bead litter for 1 hour had no effect on feline UPC measurements 5 . However, our study evaluated the effect of a longer duration of exposure (24 hours) to better mimic what may happen in the home environment, where litter trays may only be emptied once a day.…”

“…Although urine samples were stored under different conditions, which may have affected UPC measurements, this study only compared the difference in UPC measurements taken 24 hours apart. Moyle and others showed that storage of urine at room temperature for up to 5 days did not affect UPC measurements in both proteinuric and non‐proteinuric dogs, and Giraldi and others showed that storage of urine at room temperature for 6 hours did not affect UPC measurements in cats 5,18 . In this study, all samples were brought to room temperature before baselineUPCs were measured.…”

“…This study also only evaluated one type of non‐absorbent litter. Other non‐absorbent materials, such as non‐absorbent plastic pellets, are commonly used as a non‐invasive method of urine collection in the cat, but thus far, only exposure to this substrate for 1 hour has been evaluated 3,5 …”

“…The use of hydrophobic sand has been shown to have no affect the measurement of urine specific gravity, urinary dipstick parameters (leukocytes, nitrites, urobilinogen, protein, pH, blood, USG, ketones, bilirubin, and glucose), and urinary creatinine and corticosterone concentrations in rats 4 . A recent study documented that exposure to plastic non‐absorbent spherical pellets for 1 hour had no impact on feline UPC measurements 5 . To the authors' knowledge, no information about the pre‐analytical effect of exposure to non‐absorbent hydrophobic sand litter on UPC measurements has been reported.…”

“…4 A recent study documented that exposure to plastic non-absorbent spherical pellets for 1 hour had no impact on feline UPC measurements. 5 To the authors' knowledge, no information about the pre-analytical effect of exposure to non-absorbent hydrophobic sand litter on UPC measurements has been reported.…”