PTH and chronic kidney disease: In a study conducted by Rotondi et al. [24] on 68 CKD patients, sKl negatively correlated with PTH and P and positively correlated with Ca, and FGF23 positively correlated with PTH and P. In contrast to all these studies, Seiler et al. [25] followed 312 CKD patients with stage 2-4 for an average of 2.2 years and claimed that the sKl levels were not significantly correlated with GFR and other hormones or minerals in calcium-phosphate metabolism, and high FGF23 levels had no prognostic effect on sKl.