Thus, this prospective, observational study aimed to 1) assess changes in FGF23, soluble α-klotho (sKl) and other BMM markers, 2) examine alterations in PWV and 3) assess the clinical correlates of BMM, abdominal aortic calcification (AAC) and change in arterial compliance over 12 months, comparing a cohort of non-dialysis CKD stages 4 and 5 patients to healthy controls. Here, KL is linked to chronic kidney disease.