The Effect of Feeding a Renal Diet on Plasma Fibroblast Growth Factor 23 Concentrations in Cats with Stable Azotemic Chronic Kidney Disease

Background Fibroblast growth factor 23 ( FGF ‐23) is a phosphatonin, which is increased in cats with azotemic CKD . Dietary phosphate restriction decreases FGF ‐23 concentrations in humans and rodents, but this relationship has not previously been examined in the cat. Objectives To investigate the effect of feeding renal diet on plasma FGF ‐23 concentrations in cats with stable azotemic CKD . Animals Azotemic, client‐owned cats (≥9 years); 33 cats ate renal diet ( RD group) and 11 cats did not eat renal diet (comparator group) over 28–56 days. Methods Retrospective longitudinal study: Plasma FGF ‐23, PTH , and phosphate concentrations were measured at baseline and after 28–56 days. Cats in the RD group were classified as hyperphosphatemic ( HP ) or normophosphatemic ( NP ) based on the I nternational R enal I nterest S ociety targets for plasma phosphate concentration. Nonparametric tests were performed. Results In the HP group (n = 15), feeding renal diet was associated with a significant decrease in plasma phosphate ( P  = .001), PTH ( P  = .007), and FGF ‐23 ( P  = .008), but not creatinine concentrations ( P  = .91). In the NP group (n = 18), feeding renal diet was associated with a significant decrease in plasma FGF ‐23 ( P  = .006), but not phosphate ( P  = .48), PTH ( P  = .35), or creatinine concentrations ( P  = .10). No significant changes were seen in any parameters in the comparator group during the study period. Conclusions and Clinical Importance Feeding renal diet is associated with reductions in plasma FGF ‐23 concentrations in hyper‐ and normophosphatemic cats with stable azotemic CKD , suggesting that dietary phosphate restriction may enable cats with CKD to maintain normal plasma phosphate concentrations in association with lower plasma FGF ‐23 concentrations.