Analytical validation of a human particle-enhanced nephelometric assay for cystatin C measurement in feline serum and urine.
BACKGROUND
In people and dogs, Cystatin C (CysC), a renal glomerular and tubular marker, seems superior to serum creatinine to estimate the glomerular filtration rate (GFR). A particle-enhanced nephelometric immunoassay is available to measure human CysC, but there are no reports in cats.


OBJECTIVE
The goal of this study was the validation of the human CysC nephelometric assay with feline serum and urine, and to perform a pilot study comparing serum and urine CysC between healthy cats and cats with chronic kidney disease (CKD).


METHODS
Western blot analysis was used to assess cross-reactivity between the polyclonal rabbit anti-human CysC antibody and feline CysC. Imprecision and linearity were determined for feline serum and urine CysC. Serum and urine CysC were measured in 10 healthy and 10 CKD cats.


RESULTS
Cross-reactivity between the polyclonal rabbit anti-human CysC antibody and feline CysC was demonstrated. Intra- and inter-assay coefficients of variation in feline serum and urine were 1.3% and 0.4%, and 12.5%, and 4.1%, respectively. Cats with CKD had a significantly higher serum CysC concentration (1.24 [0.63-2.99] vs 0.79 [0.43-1.05] mg/L; P = .02) and urine CysC/urinary Creatinine (uCr) ratio (565.6 [0-1311] vs < 0.049/uCr mg/mol; P = .005) compared with healthy cats.


CONCLUSIONS
The human nephelometric assay showed satisfactory validation results for feline CysC. Cats with CKD had a significantly higher sCysC concentration and uCysC/uCr ratio compared with healthy cats. Additional studies are necessary to evaluate CysC as an early marker of renal damage in cats.
Department of Medicine and Clinical Biology of Small Animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
Liesbeth F E
LF
Ghys
Evelyne
E
Meyer
Dominique
D
Paepe
Joris
J
Delanghe
Sylvie
S
Daminet
D000818:Animals; D000906:Antibodies / Q000276:immunology*; D015415:Biomarkers / Q000097:blood / Q000652:urine; D002371:Cat Diseases / Q000097:blood / Q000175:diagnosis*; D002415:Cats; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000097:blood* / Q000652:urine; D005260:Female; D005919:Glomerular Filtration Rate / Q000662:veterinary*; D006801:Humans; D007118:Immunoassay / Q000379:methods / Q000662:veterinary; D008297:Male; D009391:Nephelometry and Turbidimetry / Q000379:methods / Q000662:veterinary*; D010865:Pilot Projects; D011817:Rabbits; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000175:diagnosis / Q000662:veterinary*; D015203:Reproducibility of Results
D000906:Antibodies; D015415:Biomarkers; D055316:Cystatin C; D003404:Creatinine
Biomarker; Western blot analysis; cat; chronic kidney disease; immunoassay