Urinary Protein/Creatinine Ratio in Feline Medicine: Reasons to Perform It and Its Role in Clinical Practice—A Retrospective Study

SIMPLE SUMMARY: Urinary protein/creatinine ratio allows veterinary clinicians to quantify proteinuria, i.e., the amount of protein that is lost in urine. This ratio is commonly performed in daily practice for several medical reasons, namely the diagnosis and the monitoring of feline chronic kidney disease. This study aimed at understanding the main reasons to perform UPCR in cats, correlating it with signalment, exploring the agreement between UPCR, urine dipstick protein value, and urine specific gravity and assessing its role in chronic kidney disease diagnosis and monitoring. A retrospective study was conducted, including medical data from cats consulted in a veterinary teaching hospital over two years and submitted to UPCR measurement. A total of 140 cats were included: 35% were non-proteinuric, 25% borderline proteinuric, and 40% showed overt proteinuria. This study found that UPCR is mainly requested for the diagnosis and the monitoring of chronic kidney disease and proteinuric cats with kidney disease have a worse outcome at 6-months and at 12-months. This study found and reinforced the negative prognostic value of UPCR in cats in comparison to dipstick and urine specific gravity. ABSTRACT: This study aimed at understanding the reasons veterinarians conduct a urinary protein/creatinine ratio (UPCR) in cats, correlating it with signalment, dipstick proteinuria tests, and urine specific gravity (USG) and assessing its role in chronic kidney disease (CKD) diagnosis and monitoring. A retrospective study was conducted, including medical data from cats consulted between 2016 and 2018 in a veterinary teaching hospital and submitted to at least one UPCR measurement. A total of 140 cats were included: 35% non-proteinuric (UPCR < 0.2), 25% borderline proteinuric (0.2 < UPCR < 0.4), and 40% overtly proteinuric (UPCR > 0.4). In contrast to other studies, there was no association between UPCR and male reproductive status. UPCR was mainly requested for CKD diagnosis and monitoring. Correlation between UPCR and combined results from dipstick tests and USG was low and inconsistent. Proteinuric CKD cats had a worse outcome at both 6 (odds ratio (OR 4.04) and 12 months (OR 4.36)), and this finding was more pronounced for severely proteinuric cases in which the OR for death was 4.36 and 6.00 at 6 and at 12 months, respectively. In addition to reinforcing the negative prognostic value of proteinuria, this study stresses the low and the inconsistent agreement between UPCR and the combined results of dipstick tests and USG in cats.