Serum and urinary cystatin C in cats with feline immunodeficiency virus infection and cats with hyperthyroidism.

OBJECTIVES: The objective of this study was to investigate serum cystatin C (sCysC) and urinary cystatin C (uCysC) in cats with hyperthyroidism and cats with feline immunodeficiency virus (FIV). METHODS: Thirty cats with FIV, 26 hyperthyroid cats and 28 healthy cats were included. sCysC and uCysC:creatinine (uCysC/uCr) ratio were measured with a human particle-enhanced nephelometric immunoassay, previously validated for feline CysC measurement. Routine renal variables (serum creatinine [sCr], urine specific gravity, urinary protein:creatinine ratio [UPC]) were also measured in the three groups. RESULTS: Cats with hyperthyroidism had significantly higher sCysC and higher uCysC/uCr ratio, lower sCr and a higher UPC than healthy cats. Cats with FIV infection did not show a significantly higher sCysC concentration but had a significantly higher sCr and UPC than healthy cats. uCysC could be detected in only four of them. CONCLUSIONS AND RELEVANCE: This study demonstrated that sCysC is increased in cats with hyperthyroidism, in contrast with sCr, but not in cats with FIV. Many hyperthyroid cats, but only four cats with FIV, had an elevated uCysC/uCr ratio. Further studies may reveal if uCysC might be a valuable marker for tubular dysfunction in cats.

Long-term follow-up of renal function assessing serum cystatin C in dogs with diabetes mellitus or hyperadrenocorticism.

BACKGROUND: Serum cystatin C (sCysC) is used as biomarker for glomerular filtration rate (GFR). The effects of diabetes mellitus (DM) on renal function in dogs are unclear. Some renal variables have been evaluated in dogs with hyperadrenocorticism (HAC), but not sCysC. OBJECTIVES: The purpose of this study was the validation of a particle-enhanced nephelometric immunoassay (PENIA) for measuring canine sCysC, and to assess renal function in dogs with DM or HAC. METHODS: A PENIA was analytically validated for canine sCysC by determining imprecision and linearity. In a longitudinal 6-month study, renal function of 14 DM dogs was assessed, using serum creatinine, GFR, urinary protein-to-creatinine (UPC) ratio, urinary markers, systolic blood pressure (SBP), and sCysC, and compared to 17 healthy dogs at baseline. Furthermore, sCysC was measured at initial presentation and during a 12-month follow-up in 22 HAC dogs. RESULTS: The sCysC intra- and inter-assay variation coefficients were < 8% and highly linear (r = .997). About 33% and 67% of DM dogs had persistent proteinuria and systemic hypertension, respectively, but there were no significant differences in GFR, UPC, and urinary markers over time, and compared with healthy dogs at initial presentation. Serum CysC decreased significantly (P < .05) over time within the DM group. It did not change significantly over time within the HAC group. CONCLUSIONS: A PENIA measured sCysC linearly and precisely. There were no clinically relevant renal alterations over time in dogs with DM, although persistent proteinuria was observed. In dogs with HAC, sCysC measurement was not useful, although significant GFR changes occurred over time.

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.