In the Chronic Renal Insufficiency Cohort (CRIC) study, the median C-terminal FGF23 was 145 RU/mL (IQR 96–239) in patients with a mean eGFR of 42.8 ± 13.5 ml/min/1.73 m2 [9]. This evidence concerns the gene FGF23 and chronic kidney disease.