In a study by Isakowa et al. [9] on 3879 patients in the Chronic Renal Insufficiency Cohort Study, in early stages of renal disease, while the serum phosphate and parathormone levels were within the normal range, the FGF23 levels were significantly increased compared to a healthy population, and as the disease progressed, the increase in FGF23 became more significant, and hyperphosphatemia and secondary hyperparathyroidism developed. Here, FGF23 is linked to secondary hyperparathyroidism.