Relationship between ultrasonographically determined renal dimensions and International Renal Interest Society stages in cats with chronic kidney disease

BACKGROUND: The correlation between renal dimensions and renal function in cats with chronic kidney disease (CKD) is unclear. HYPOTHESIS/OBJECTIVES: To investigate the relationship between renal dimensions and CKD severity in cats using ultrasound examination. ANIMALS: Nineteen healthy cats and 30 cats with CKD. METHODS: Renal ultrasound images obtained between 2012 and 2016 were reviewed. Severity of CKD was determined using the International Renal Interest Society CKD staging system. Renal length, cortical thickness, medullary thickness, and corticomedullary ratio were measured, and the relationship between these renal dimensions and serum creatinine concentrations as well as differences in dimensions between the control and disease groups was investigated. The sensitivity and specificity of the renal dimensions for differentiation of the CKD also were evaluated. RESULTS: The disease group was subdivided into stage I to II (15 cats) and stage III to IV (15 cats) groups. Cortical thickness was significantly decreased in both disease groups and negatively correlated with disease severity. Compared with other renal dimensions, cortical thickness had a stronger linear correlation with the reciprocal of the serum creatinine concentration and superior diagnostic performance (Youden index: left kidney, 90.0% sensitivity and 94.7% specificity for a cutoff of 4.7 mm; right kidney, 83.3% sensitivity and 94.7% specificity for a cutoff of 4.5 mm). CONCLUSIONS AND CLINICAL IMPORTANCE: Decreased renal cortical thickness is observed in cats with loss of renal function. Measurement of cortical thickness using ultrasonography could be a useful method to evaluate the progression of CKD in cats.