Feline Renal Cortical Thickness–Aortic Diameter Ratio in Healthy Versus Diseased Kidneys: Comparative Ultrasonographic Evaluation

In this retrospective multicenter study, we aimed to establish the renal cortical thickness–aortic diameter (RCT:Ao) ratio as a diagnostic parameter for detecting feline acute kidney injury or chronic kidney disease (AKI or CKD). This study included bilateral kidneys of 152 normal, 171 CKD, 19 AKI, and 15 acute‐on‐chronic kidney disease (ACKD) cats. Ultrasonographic measurements were obtained in the midsagittal plane of the kidneys and aorta. Multiple linear regression analysis of RCT, body weight (BW), and body condition score (BCS) revealed a positive correlation of RCT with BW ( p < 0.001), but not with BCS ( p = 0.343). Multiple linear regression analysis of RCT:Ao ratio, BW, and BCS showed a poor model fit ( F value: 0.119). There were significant intergroup differences among the normal, CKD, AKI, and ACKD sub‐cohorts ( p < 0.001). Compared to normal cats, CKD and AKI cats each had lower and higher RCT:Ao ratio (both p < 0.001), respectively. The RCT:Ao ratio of the ACKD group significantly differed from that in normal and CKD groups (both p < 0.001), but not the AKI group ( p = 0.159). Optimal RCT:Ao ratio cutoffs of 1.15 and 1.45 were used to distinguish between the normal and CKD groups (75% sensitivity, 80% specificity) and the normal and AKI groups (90% sensitivity, 89% specificity), respectively. The RCT:Ao ratio was unaffected by the BW and BCS and is a clinically useful diagnostic parameter for feline kidney disease.