*2.2. Biochemical Analysis*

Serum and urinary phosphate, calcium, sodium, and creatinine were measured using a Cobas c111 analyzer (Roche, Mannheim, Germany). Serum intact FGF23 (Kainos, Tokyo, Japan), serum and urinary aldosterone (NovaTec Immundiagnostica, Dietzenbach, Germany), serum intact PTH (Immutopics Inc, San Clemente, CA, USA), and serum renin (Abbexa Ltd., Cambridge, UK) were detected using commercially available ELISA kits according to the manufacturer's instructions. Serum was extracted with diethylether and re-suspended in steroid-free serum (DRG Diagnostics, Marburg, Germany) for the aldosterone ELISA.
