FGF23 and chronic kidney disease: Elevated serum phosphorus (P) levels have been associated with cardiovascular disease (CVD) and cardiovascular mortality in chronic kidney disease (CKD) patients.(1–4) Serum P level is mainly regulated by 1,25(OH)2D, a parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23), and is maintained at 2.5–4.5 mg/dl in healthy populations.(5–7) The major cause of elevated serum P is excessive P intake under the condition of kidney dysfunction.