Phosphate control in reducing FGF23 levels in hemodialysis patients
Fig 4
The degree of influence (expressed in percent) of the various independent variables on the serum levels of iFGF23 (A) and cFGF23 (B). The proportional contribution (Relative weights; RWs) of each of the independent variables on the serum levels of FGF23 were calculated. Statistical significance of RWs were assessed as described elsewhere [38,39]. Statistical significance is based on the values of confidence intervals; if zero is excluded from the confidence interval, the RW is significant. The RWs significance test was run only for variables that showed statistical significance in the linear regression models. The proportional contribution of serum iPTH, 25 (OH) D, 1,25 (OH) 2 D, ferritin, calcium dialysate, the use of cinacalcet or paricalcitol, calcium-based, and calcium-free phosphate binders are grouped as “others” since their individual contribution was limited. S4 Table shows the detailed proportionate contribution of each variable for the entire population and separated according to phosphate levels below or above the median. Lowercase letters above columns identify different groups analyzed, a1-b1 overall population, a2-b2 patients with P<4.35 mg/dL and a3-b3 patients with P>4.35 mg/dL for iFGF23 and cFGF23 respectively. For iFGF23 (A) RWs of serum phosphate (CI for significance 0.24–0.47), ionized calcium [iCa] (CI for significance 0.001–0.07) and hs-CRP (CI for significance 0.01–0.10) were significantly different in the entire population (a1). Moreover, RWs of serum phosphate was significantly greater than the RWs of iCa, hs-CRP and age RWs`. In patients with P<4.35 mg/dL (a2), RWs of serum iCa (CI for significance 0.01–0.26) and phosphate (CI for significance 0.14–0.41) were significant as compared to the other variables. Interestingly, there was no difference between the RWs of phosphate and iCa in this group of patients (a2). In patients with phosphate above the median (P>4.35 mg/dL) [a3], only the RWs of hs-CRP (CI for significance 0.00–0.12) and phosphate (CI for significance 0.06–0.45) were significant. The RW of phosphate (59.9%) was significantly greater than that of the RWs of age (CI for significance -0.45—-0.04), hs-CRP (CI for significance -0.44—-0.02), and iCa (CI for significance -0.49—-0.07). (B) Regarding cFGF23, in the overall population (b1) serum phosphate remained to be the main contributor (40.6%). Together with phosphate (CI for significance 0.18–0.34), RWs of hs-CRP (CI for significance 0.10–0.26), dialysis vintage (CI for significance 0.01–0.14), and age (CI for significance 0.008–0.12) were also significant. RWs of phosphate and hs-CRP were not different (CI for significance -0.20–0.04). Contribution of hs-CRP was far more important than that of iCa (31.0 vs 1.0%); (b1). In the group of patients with P<4.35 mg/dL (b2), hs-CRP (CI for significance 0.09–0.40) and phosphate (CI for significance 0.02–0.20) were the two significant RWs. hs-CRP contributed far more than phosphate, age and dialysis vintage. Finally, in the group of patients with P>4.35 mg/dL (b3), dialysis vintage (CI for significance 0.05–0.32), hs-CRP (CI for significance 0.01–0.17), and serum phosphate (CI for significance 0.03–0.31) were the significant RWs. There were no differences between RWs of these three variables.