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

O bjectives : 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. M ethods : 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). R esults : 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. C linical S ignificance : 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.