KL and kidney failure: Lima et al. reported that there was an increase in serum FGF-23 levels in patients with CKD starting from the early stages.14 Manou et al. reported in their study that as the renal failure stage progressed in patients with CKD, the increase in serum FGF-23 levels was accompanied by a decrease in the coreceptor s-KL levels.15 Shou et al. reported that increased serum FGF-23 levels in patients with advanced-stage CKD were accompanied by an increase in serum PTH levels, along with a decrease in 1.