AIM: Active vitamin D (1,25-dihydroxyvitamin D₃), PTH, fibroblast growth 
factor-23 (FGF-23) and Klotho protein are key regulators of phosphate 
metabolism. Hyperphosphatemia and increased FGF-23 level in patients with 
end-stage renal disease are associated with increased morbidity and mortality. 
The relationships among key regulators of phosphate metabolism are still being 
investigated. FGF-23, the humoral factor involved in phosphate metabolism, is 
strongly associated with serum phosphorus level. Klotho, a transmembrane protein 
expressed primarily in renal tubules, functions as an obligatory co-receptor for 
FGF-23. The soluble form of Klotho, produced by the shedding of the 
transmembrane protein, is detectable in body fluids. The purpose of the study 
was to assess if serum soluble alpha-Klotho level was related to phosphate 
metabolism parameters and residual renal function (RRF) in incident peritoneal 
dialysis (PD) patients.
METHODS: Thirty-five clinically stable patients 4 to 6 weeks after the onset of 
PD were included in the study. For each patient, clinical and laboratory data 
were reviewed. Serum phosphorus concentration, urinary and peritoneal phosphate 
clearance, serum FGF-23 and soluble Klotho protein concentrations were 
determined.
RESULTS: Serum soluble alpha-Klotho was strongly negatively correlated with 
24-hour diuresis (Rs = -0.55, p = 0.004) and renal phosphate clearance (Rs = 
-0.40, p = 0.049), but not with RRF.
CONCLUSIONS: Serum soluble Klotho protein concentration is inversely related to 
residual diuresis and renal phosphate clearance in incident PD patients.