Association between serum fibroblast growth factor‐23 concentration and development of hyperphosphatemia in normophosphatemic dogs with chronic kidney disease

BACKGROUND: Fibroblast growth factor (FGF)‐23 is increased first in the sequence of changes associated with chronic kidney disease (CKD)‐mineral and bone disorder. Thus, its measurement may serve as a predictive indicator of incident hyperphosphatemia. OBJECTIVES: To investigate whether serum FGF‐23 concentration in normophosphatemic dogs with CKD is associated with the risk of the subsequent development of hyperphosphatemia and CKD progression. ANIMALS: Forty‐two normophosphatemic dogs with CKD. METHODS: Blood samples and medical records were retrospectively investigated. Hyperphosphatemia was defined as a serum phosphorous concentration >5.0 mg/dL. Progression was defined as a >1.5‐fold increase in serum creatinine concentration. The time periods and hazard ratios for these outcomes were assessed using Kaplan‐Meier analysis, log‐rank test, and univariate Cox regression analysis. The variables associated with the outcomes in the univariate analysis were included in the multivariate Cox regression model with backward selection. RESULTS: Serum FGF‐23 concentration >528 pg/mL was associated with a shorter time to development of hyperphosphatemia (P < .001) and CKD progression (P < .001). In multiple Cox regression analysis, increased FGF‐23 concentration remained a significant variable associated with these outcomes (P < .05). CONCLUSIONS AND CLINICAL IMPORTANCE: Increased FGF‐23 concentration in normophosphatemic dogs with CKD was associated with significant risk of development of hyperphosphatemia, independent of CKD stage, and of the progression of CKD. Future research focusing on whether interventions that decrease FGF‐23 secretion will slow the development of hyperphosphatemia and CKD progression is needed.