Evaluation of Cystatin C for the Detection of Chronic Kidney Disease in Cats.

Abstract

BACKGROUND: Serum cystatin C (sCysC) and urinary cystatin C (uCysC) are potential biomarkers for early detection of chronic kidney disease (CKD) in cats. An in-depth clinical validation is required. OBJECTIVES: To evaluate CysC as a marker for CKD in cats and to compare assay performance of the turbidimetric assay (PETIA) with the previously validated nephelometric assay (PENIA). ANIMALS: Ninety cats were included: 49 CKD and 41 healthy cats. METHODS: Serum CysC and uCysC concentrations were prospectively evaluated in cats with CKD and healthy cats. Based on plasma exo-iohexol clearance test (PexICT), sCysC was evaluated to distinguish normal, borderline, and low GFR. Sensitivity and specificity to detect PexICT&#xa0;<&#xa0;1.7&#xa0;mL/min/kg were calculated. Serum CysC results of PENIA and PETIA were correlated with GFR. Statistical analysis was performed using general linear modeling. RESULTS: Cats with CKD had significantly higher mean&#xa0;&#xb1;&#xa0;SD sCysC (1.4&#xa0;&#xb1;&#xa0;0.5&#xa0;mg/L) (P&#xa0;<&#xa0;.001) and uCysC/urinary creatinine (uCr) (291&#xa0;&#xb1;&#xa0;411&#xa0;mg/mol) (P&#xa0;<&#xa0;.001) compared to healthy cats (sCysC 1.0&#xa0;&#xb1;&#xa0;0.3 and uCysC/uCr 0.32&#xa0;&#xb1;&#xa0;0.97). UCysC was detected in 35/49 CKD cats. R(2) values between GFR and sCysC or sCr were 0.39 and 0.71, respectively (sCysC or sCr&#xa0;=&#xa0;&#x3bc;&#xa0;+&#xa0;GFR&#xa0;+&#xa0;&#x3b5;). Sensitivity and specificity were 22 and 100% for sCysC and 83 and 93% for sCr. Serum CysC could not distinguish healthy from CKD cats, nor normal from borderline or low GFR, in contrast with sCr. CONCLUSION: Serum CysC is not a reliable marker of reduced GFR in cats and uCysC could not be detected in all CKD cats.