Calcium and phosphate homeostasis in hyperthyroid cats: associations with development of azotaemia and survival time.

OBJECTIVES: To evaluate calcium and phosphate homeostasis in hyperthyroid cats and determine if plasma parathyroid hormone and fibroblast growth factor-23 are associated with the presence of -azotaemic chronic kidney disease and/or have prognostic significance.

METHODS: Retrospective cohort study. Logistic regression analysis and Cox regression analysis were performed to identify if parathyroid hormone and fibroblast growth factor-23 were predictors of development of azotaemia following treatment and survival time, respectively.

RESULTS: Two hundred and seven hyperthyroid cats were included. Elevated plasma parathyroid hormone concentrations, hyperphosphataemia, decreased plasma fibroblast growth factor-23 concentrations and hypocalcaemia were documented; however, all parameters returned to reference intervals following treatment of hyperthyroid cats without azotaemic chronic kidney disease. After adjustment for plasma creatinine concentration, baseline plasma parathyroid hormone and fibroblast growth factor-23 concentrations were not predictors of the development of azotaemia following treatment. Baseline plasma fibroblast growth factor-23 concentrations were associated with all-cause mortality; however, this association was not maintained after adjustment for packed cell volume.

CLINICAL SIGNIFICANCE: Changes in plasma parathyroid hormone and fibroblast growth factor-23 concentrations which occur in hyperthyroid cats are not mediators of progression of chronic kidney disease; however, fibroblast growth factor-23 would appear to have some prognostic significance in hyperthyroidism.