LAUSR

Objectives This study investigated whether serum fibroblast growth factor (FGF)-23 concentrations are associated with serum total calcium (tCa) and blood ionised calcium (iCa) concentrations in cats with chronic kidney disease (CKD) and upper urolithiasis. Methods Serum samples and the medical records of cats with CKD with nephroliths, ureteroliths or both were investigated retrospectively. Cats with a serum creatinine concentration >250 μmol/l and/or a serum phosphorus concentration ⩾1.50 mmol/l were excluded. Based on cut-offs for serum tCa (2.70 mmol/l) or blood iCa (1.40 mmol/l), cats were divided into the following groups: total hypercalcaemia (H-tCa) (>2.70 mmol/l) and total normocalcaemia (N-tCa) (⩽2.70 mmol/l) groups, or ionised hypercalcaemia (H-iCa) (>1.40 mmol/l) and ionised normocalcaemia (N-iCa) (⩽1.40 mmol/l) groups, respectively. Serum FGF-23 concentrations were compared between groups and correlation analysis was performed. Results Thirty-two cats with CKD and upper urolithiasis were included. Serum FGF-23 concentrations in the H-tCa group (median 573 pg/ml [range 125–3888]; n = 12) were significantly higher compared with the N-tCa group (median 245 pg/ml [range 94–627]; n = 20) (P = 0.001). Serum FGF-23 concentrations in the H-iCa group (median 1479 pg/ml [range 509–3888]; n = 6) increased significantly compared with the N-iCa group (median 245 pg/ml [range 94–637]; n = 26) (P <0.001). Serum FGF-23 concentrations significantly correlated with serum tCa (r = 0.511, P = 0.003) and blood iCa concentrations (r = 0.425, P = 0.015) but not serum creatinine (r = 0.279, P = 0.122) or phosphorus concentrations (r = 0.208, P = 0.253).Conclusions and relevance Increased serum FGF-23 concentrations were associated with hypercalcaemia independently of creatinine and phosphate status in cats with CKD and upper urolithiasis.