Relationship between Plasma Fibroblast Growth Factor‐23 Concentration and Survival Time in Cats with Chronic Kidney Disease

BACKGROUND: Fibroblast growth factor‐23 (FGF‐23) and parathyroid hormone (PTH) are commonly increased in cats with azotemic chronic kidney disease (CKD). Both are predictors of survival time in human patients, but these relationships have not previously been examined in the cat. OBJECTIVES: To investigate the relationship between plasma FGF‐23 and PTH concentrations at diagnosis of CKD in cats with survival time and with disease progression over 12 months. ANIMALS: 214 azotemic, client‐owned cats (≥9 years). METHODS: Retrospective study: Biochemical and urinary variables at diagnosis of azotemic CKD, including plasma FGF‐23 and PTH concentrations were assessed as predictors of survival time (all‐cause mortality) using Cox regression, and as predictors of CKD progression over 12 months using logistic regression. RESULTS: In the final multivariable Cox regression model, survival was negatively associated with plasma creatinine (P = .002) and FGF‐23 concentrations (P = .014), urine protein‐to‐creatinine ratio (P < .001) and age (P < .001). Survival was positively associated with PCV (P = .004). In the final multivariable logistic regression model, independent predictors of CKD progression included logFGF‐23 and age. Neither plasma phosphate nor PTH was found to be an independent predictor of survival time or of CKD progression. CONCLUSIONS AND CLINICAL IMPORTANCE: Plasma FGF‐23 concentration is a novel prognostic indicator in cats with CKD, independent of other factors including plasma creatinine and phosphate concentrations. Further work is required to assess if FGF‐23 contributes directly to CKD progression, but regardless these findings may make FGF‐23 a useful biomarker for predicting poorer outcomes in cats with CKD.