Quantitative Evaluation of Urine Protein-to-Creatinine Ratio in Dogs With Sporadic Bacterial Cystitis

Background/Aim: Proteinuria is a key indicator of canine renal disease. While bacterial cystitis causes post-renal proteinuria, the extent to which sporadic bacterial cystitis increases the urine protein-to-creatinine ratio (UPC) is not well defined. This study aimed to quantitatively evaluate the effect of sporadic bacterial cystitis on the canine UPC and determine whether the UPC can distinguish sporadic infection from renal proteinuria. Materials and Methods: A retrospective study was conducted on dogs evaluated between 2016 and 2025. The study included healthy dogs (n=37), dogs with sporadic bacterial cystitis (n=13), bacterial cystitis with comorbidities (n=65), chronic kidney disease (CKD; n=26), and hyperadrenocorticism (HAC; n=15). Results: The median UPC in the sporadic bacterial cystitis group (0.20) showed no significant difference compared to healthy dogs (0.20; p=0.392). Conversely, dogs with bacterial cystitis with comorbidities (0.62) and those with CKD or HAC (0.73) exhibited significantly higher UPCs than the sporadic infection group (p<0.001). Distinguishing sporadic infection from renal proteinuria yielded an area under the curve of 0.9373, with an optimal cut-off of 0.425 (100% specificity, 73.2% sensitivity). Conclusion: Sporadic bacterial cystitis alone does not cause clinically significant increases in the UPC in dogs. A UPC exceeding 0.32 in dogs with cystitis should prompt further investigation for underlying diseases, and a UPC greater than 0.425 suggests renal proteinuria. This approach prevents the misattribution of proteinuria and supports the timely diagnosis of renal diseases.