Risk factors associated with disturbances of calcium homeostasis after initiation of a phosphate‐restricted diet in cats with chronic kidney disease

BACKGROUND: Dietary phosphate restriction improves survival in cats with chronic kidney disease (CKD). However, feeding a phosphate‐restricted diet may disrupt calcium homeostasis leading to hypercalcemia in some cats. OBJECTIVES: To identify risk factors associated with increasing plasma total calcium (tCa) concentration after transition to a phosphate‐restricted diet and to explore its role in CKD‐mineral and bone disorder (CKD‐MBD) in cats. ANIMALS: Seventy‐one geriatric (≥9 years) euthyroid client‐owned cats with International Renal Interest Society (IRIS) stage 2 to 3 azotemic CKD. METHODS: Retrospective cross‐sectional cohort study. Changes in plasma tCa concentration in the first 200 days of diet transition were assessed using linear regression. Binary logistic regressions were performed to identify risk factors for increasing calcium concentration. Changes in clinicopathological variables associated with CKD‐MBD over time were explored using linear mixed model and generalized linear mixed model analyses. RESULTS: Lower baseline plasma potassium (odds ratio [OR] = 1.19 per 0.1 mmol/L decrease; P = .003) and phosphate (OR = 1.15 per 0.1 mmol/L decrease; P = .01) concentrations remained independent risk factors for increasing plasma tCa concentration. Plasma creatinine (β = .069 ± .029 mg/dL; P = .02), symmetric dimethylarginine (β = .64 ± .29 μg/dL; P = .03), phosphate (β = .129 ± .062 mg/dL; P = .04), and ln[FGF23] (β = .103 ± .035 pg/mL; P = .004) concentrations had significantly increased rates of change in cats with increasing plasma tCa concentration over time. CONCLUSION AND CLINICAL IMPORTANCE: Lower plasma potassium or phosphate concentrations or both at the time of transition of cats with CKD to a phosphate‐restricted diet are independently associated with increased risk of an increase in plasma tCa concentration. Increasing plasma tCa concentration is associated with progression of CKD.