Renal Cortical Thickness and Derived Ratios as Superior Ultrasonographic Markers for Detecting Feline Chronic Kidney Disease

Chronic kidney disease (CKD) is one of the most common diseases in cats, and detection of CKD is essential for its management. The objectives of this study are to compare ultrasonographic renal parameters between clinically healthy cats and those with CKD; to evaluate the correlations between ultrasonographic renal parameters and renal biomarkers, including blood urea nitrogen (BUN), creatinine (Cr), symmetric dimethylarginine (SDMA), age, sex, and body weight; and determine the diagnostic cutoff values. Sixty cats (30 clinically healthy and 30 cats with CKD) were engaged. Cross-sectional and observational studies were conducted. Ultrasonographic parameters including renal cortical thickness (RCT), medullary thickness (MT), renal length (RL), abdominal aorta diameter (Ao) and their ratios (RCT/Ao, RCT/MT, RCT/RL, MT/Ao, RL/Ao) were evaluated. Correlations with BUN, Cr, SDMA, and demographic data were analyzed. The cutoff values were calculated. The results show that RCT, RCT/Ao, RCT/MT, and RCT/RL were significantly lower in CKD cats, especially on the transverse plane (p < 0.001). The MT and MT/Ao ratios were significantly lower on only the dorsal plane (p = 0.0009 and 0.022, respectively). RL was significantly lower in cats with CKD (p = 0.03). RCT and its ratios showed stronger negative correlations with BUN, Cr, and SDMA than with MT or RL. Age, body weight, and sex are not influece to ultrasonographic parameters. Diagnostic performance in CKD classification of RCT and its ratios were significantly higher than MT, MT/Ao, RL and RL/Ao. In conclusion, RCT and its derived ratios are promising key ultrasonographic parameters in the clinical evaluation and monitoring of feline CKD.