Urine protein-to-creatinine (UPC) ratios are used to quantify proteinuria and to stage renal diseases or monitor efficacy of treatments. Studies have positively correlated the progression of kidney disease with the degree of proteinuria, and the International Renal Interest Society (iris-kidney.com) has developed guidelines that diagnose and stage chronic kidney disease according to serum creatinine concentrations, systemic blood pressure, and UPC ratios. Many reports suggest that UPC ratios are reliable only if the urine samples are obtained via cystocentesis. Cystocentesis has its disadvantages, such as risk for bladder tearing or rupture, the need for manual restraint, and difficulty localizing the bladder in some dogs. This study compared UPC ratios obtained via cystocentesis and via free catch in the same dog. Included in the study were 115 client-owned dogs. Dogs were screened to ensure that cystitis, bladder/urethral tumors, and genital disorders were not present. A total of 230 urine samples were collected and 34 dogs were excluded because of urine sediment, indicating active inflammation. Overall, UPC ratios correlated highly regardless of sampling technique. More important, none of the cystocentesis-collected samples with UPC ratios indicating proteinuria had a paired free-catch sample with UPC ratios indicating no proteinuria. Diagnostic information obtained by urinalysis on voided samples was equal to that obtained on samples collected by cystocentesis. The authors concluded that a UPC ratio can be reliably measured from urine with an inactive sediment, regardless of sample collection technique.

Commentary: At my hospital, UPC ratios are commonly added to samples submitted at the time of urinalysis and culture (and urine is usually obtained by cystocentesis). Many doctors also encourage owners to have repeat measurements performed on cystocentesis samples. Samples obtained via cystocentesis are also more expensive. However, this report suggests that an owner can simply drop off a free-catch sample for urinalysis and a UPC ratio. If the sediment appears inactive, a UPC ratio can be added on with reliable accuracy. This will make monitoring proteinuric dogs simpler for owners and for veterinarians.

Comparison of urine protein-to-creatinine ratio in urine samples collected by cystocentesis versus free catch in dogs. Beatrice L, Nizi F, Callegari D, et al. JAVMA 236:1221-1224, 2010.