Urinary Fibroblast Growth Factor-23 and Soluble Alpha-Klotho in Cats with Chronic Kidney Disease.

Fibroblast growth factor 23 (FGF23) and α-Klotho play crucial roles in the pathogenesis of chronic kidney disease-mineral and bone disorder (CKD-MBD) due to their regulatory effects on phosphorus, calcium, parathyroid hormone, and calcitriol levels. Despite their importance, few studies have examined urinary concentrations of these compounds in feline chronic kidney disease (CKD), thereby limiting our understanding of their roles in disease progression. This study aimed to evaluate the urinary levels of FGF23 (uFGF23) and soluble α-Klotho (uKL) in cats at various stages of CKD, including acute decompensated chronic kidney disease (ACKD), and to assess their respective relationship with disease progression. We quantified these levels using commercial ELISA kits in a cohort of 13 healthy cats, 71 CKD cats, and 28 ACKD cats. Our results revealed a significant elevation of uFGF23-to-urine-creatinine ratio with late CKD (median: 7.08 ×10-7) and ACKD (10.9 ×10-7) cats compared to early CKD cats (2.91 ×10-7, p = 0.005 and p < 0.001, respectively) and healthy cats (0.86 ×10-7, p < 0.001 in both comparisons). The urinary Klotho/FGF23 ratio exhibited a progressive decline from healthy cats (0.144) to early-stage CKD cats (0.108, p = 0.014), and thence to late-stage CKD cats (0.094, p = 0.039). Lower tertiles of uKL levels were identified as an independent prognostic factor for CKD progression (hazard ratio: 8.49, p = 0.004). In conclusion, these findings suggest that uFGF23, uKL, and their ratio may serve as useful biomarkers for assessing CKD and predicting CKD progression in cats.