Serum fibroblast growth factor 23 (FGF-23): associations with hyperphosphatemia and clinical staging of feline chronic kidney disease.

Abstract

Fibroblast growth factor 23 (FGF-23) is an independent monitor of the progression of chronic kidney disease (CKD) in human medicine, and FGF-23 may have value as a biomarker in feline CKD. We evaluated the relationship between serum FGF-23 and CKD stages, and the effect of age on FGF-23 in normal cats. We measured FGF-23 and intact parathyroid hormone (iPTH) concentrations by ELISA, with intra- and inter-assay CVs &#x2264; 15%. The percentage recovery of FGF-23 and iPTH remained stable for up to 7 d in samples stored at -20&#xb0;C and -80&#xb0;C. We measured FGF-23 in 304 cats, among which 196 were diagnosed with CKD. The 108 clinically healthy cats were divided into 5 subgroups based on growth stage (0-2&#x2009;y, 3-6&#x2009;y, 7-10&#x2009;y, 11-14&#x2009;y, &#x2265; 15&#x2009;y). No statistical difference was found in FGF-23 among age groups (= 0.15) or by sex in healthy subjects. Using the International Renal Interest Society guideline, 34 cats were defined as CKD stage 1, 74 stage 2, 51 stage 3, and 37 stage 4. FGF-23 was higher in cats in all CKD stages than in controls. Higher serum phosphorus was observed in stage 3 (= 0.04) and 4 (< 0.01) compared to controls. iPTH increased as CKD progressed. Pearson analysis indicated a positive linear relationship between FGF-23 and iPTH (control:= 0.70,< 0.01; CKD:= 0.46,= 0.02). FGF-23 may be a useful biomarker of feline CKD and may precede hyperphosphatemia in advanced feline CKD.