Vitamin D and Vitamin-D-Binding Protein Kinetics in Patients Treated with Continuous Ambulatory Peritoneal Dialysis (CAPD)

Abstract

Serum and dialysate levels of 25-hydroxycholecalciferol (25-0HD3), 1,25 dihydrox ycholecalciferol (1,25(0H)2D3), and vitamin-D-binding protein (DBP) were measured in 14 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Serum levels of 25-0HD3 and DBP were within normal range (29.1 ± 22.9 nmollL and 5.9 ± 1.1 μmol/L, respectively). Serum levels of 1,25-(0H)2D3 were subnormal in all «16 pmol/L) but one. In 5 patients, dialysate concentrations of 25-0HD3 were 2.3 ± 0.9 nmol/L, the rest had levels <1.0 nmol/L. Small quantities of 1,25-(0H)2D3 were found in the dialysate effluents. DBP could be detected in the dialysate in all patients (0.24 ± 0.06 μmol/L). Mass transfer (MT) of 25-0HD3 and DBP were respectively -10.4 ± 8.3 nmol/24 h and -1.46 ± 0.46 μmol/24 h. Peritoneal clearances of 25-0HD3 and DBP were low (0.40 ± 0.37 mL/min and 0.18 ± 0.06 mL/ min, respectively. We conclude that CAPD leads to losses of 25-0HD3 and DBP. However, the peritoneal loss of DBP is well compensated and does not result in serum deficiency. Serum 25-0HD3 levels did not correlate with time on CAPD.