Initial evaluation of canine urinary cystatin C as a marker of renal tubular function

Objectives: To evaluate the performance of a particle-enhanced turbidimetric assay for measuring canine urinary cystatin C and to investigate if the urinary cystatin C to creatinine ratio is higher in dogs with renal disease than in non-renal disease dogs. Methods: Urinary cystatin C was measured by particle-enhanced turbidimetric assay using an avian antihuman cystatin C antibody and the performance of this assay was evaluated. Clinical relevance was tested in 46 dogs that were divided into three groups: healthy dogs (n=14), non-renal disease dogs (n=17) and dogs with renal disease (n=15). Results: The assay was linear (R2=0.99) and precise (mean intra- and inter-assay coefficients of variation were 2.3 and 2.9%, respectively). The recovery was 111.5% and the limit of blank was 0.02 mg/L. Urinary cystatin C and urinary cystatin C to creatinine ratio differed significantly (P<0.001) between the three cohorts of dogs. Clinical Significance: Measurement of cystatin C by particle-enhanced turbidimetric assay performed with high precision and linearity. This assay can be processed on automated clinical chemistry analysers making it widely available to commercial laboratories. Urinary cystatin C to creatinine ratio can differentiate dogs with renal disease from dogs without renal disease. These preliminary results suggest that urinary cystatin C to creatinine ratio is a promising marker for evaluating renal tubular function.