FGF23 and chronic kidney disease: Aim of this prospective, randomized clinical pilot study was to evaluate effect of oral spherical carbonaceous adsorbent renaltec (PorusOne, Porus) on IS plasma concentration, progression of CKD (increase in IRIS stage or >25% creatinine increase), parameters of calcium/phosphate homeostasis (tCa, phosphorus, FGF23), urine protein/creatinine ratio (UP/C), and fecal dysbiosis index (FDI) in cats with stable CKD IRIS Stage 2 and 3.