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

BackgroundSerum 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. ObjectivesThe 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. MethodsA 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. ResultsThe 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. ConclusionsA 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.