• Azotemia;
  • Feline;
  • GFR ;
  • Renal secondary hyperparathyroidism


Fibroblast growth factor (FGF-23) has an important role in phosphate regulation. Its clinical relevance in cats with CKD has not been explored previously.


The study objectives were (1) to determine whether FGF-23 concentrations are increased in nonazotemic cats, cats which developed azotemia within 12 months of screening compared with cats that remained non-azotemic, and (2) to evaluate the relationships between FGF-23 and PTH and FGF-23 and glomerular filtration rate (GFR).


Sixty-two healthy client-owned geriatric cats, 14 of which developed azotemia during the 12-month follow-up period.


Healthy nonazotemic cats were recruited prospectively into the study and followed for 12 months. At the study end-point, cats were categorized into 3 groups according to plasma creatinine concentration. PTH, FGF-23, and additional biochemical variables were evaluated at baseline and after 12 months. GFR was measured by a corrected slope-intercept iohexol clearance method.


FGF-23 concentrations at baseline were found to be significantly increased in cats that developed azotemia (P = .001) compared with cats that did not develop azotemia. A significant positive relationship was identified between FGF-23 and PTH, whereas the relationship between FGF-23 and GFR was negative.

Conclusions and Clinical Importance

FGF-23 concentrations predicted development of azotemia in geriatric cats. Positive relationships between FGF-23 and PTH suggest an association between FGF-23 and renal secondary hyperparathyroidism.