Effect of post-dilutional on-line haemodiafiltration on serum calcium, phosphate and parathyroid hormone concentrations in uraemic patients

Background. Strict control of serum calcium and phosphate concentrations is paramount to prevent secondary hyperparathyroidism in haemodialysis (HD) patients. Standard intermittent low-flux HD (Lf-HD) is not sufficient to reach this goal. The aim of this study was to evaluate the effect of on-line haemodiafiltration (Ol-HDF) on serum calcium (sCa), phosphate (sPO4) and parathyroid hormone (PTHint) concentrations. Methods. Of the 220 patients screened, 65 met the inclusion criteria for the study; 30 of whom agreed to participate in the study (Study group), the others were considered as the control group (Controls). Protocol for Study the group consisted of 6 months conventional Lf-HD (Period 1) and 6 months of post-dilutional Ol-HDF (Period 2). Controls continued their usual Lf-HD and were followed for 12 months. The main variables evaluated at the start and at the end of each period were sCa, sPO(4) and PTHint. Results. The switchover from Lf-HD to Ol-HDF resulted in a significant reduction of sPO4 (from 5.1 +/- 1.0 to 4.0 +/- 0.7; P < 0.0001) and PTHint concentrations (from 307 +/- 167 to 194 +/- 98; P < 0.0001), no significant changes were found in both sCa concentrations (from 9.1 +/- 0.7 to 8.9 +/- 0.6) and phosphate binder dose. Kt/Vurea increased significantly, and beta(2) microglobulin concentrations decreased significantly. In the Controls, no significant variations of the same variables were observed over time, except for a significant increase in sevelamer intake. Conclusion. This study supports the idea that Ol-HDF could be better than Lf-HD in controlling mineral metabolism in HD patients.