FGF23 and secondary hyperparathyroidism: Decreasing eGFR is associated with secondary hyperparathyroidism, abnormalities in 1,25-dihydroxy vitamin D synthesis, hyperphosphatemia, chronic metabolic acidosis, and elevated sclerotia and/or fibroblast growth factor 23 (FGF-23) levels, which results in the bone absorption and formation [18–21].