Minerals, vitamin D, and parathyroid hormone in continuous ambulatory peritoneal dialysis

The effects of continuous ambulatory peritoneal dialysis on parathyroid hormone (PTH) and mineral metabolism were evaluated in ten patients. Utilizing a PTH radioimmunoassay, which measures both intact hormone and carboxyl-terminal PTH fragments, it was found that the mean clearance of immunoreactive parathyroid hormone was 1.5 +/- 0.73 ml/min (SEM) yielding a daily net removal of 13.6 +/- 3.2% of estimated total extracellular parathyroid hormone. Gel electrophoresis of the dialysate revealed the presence of both intact parathyroid hormone and fragments in a similar pattern to that of peripheral plasma. Normal levels of 25-(OH) vitamin D and vitamin D binding protein were observed prior to the initiation of continuous ambulatory peritoneal dialysis and following 6 months of treatment. Timed dialysate collections (N = 93) demonstrated a daily calcium influx of only 9.9 +/- 9.7 mg. The daily removal of phosphorus was 308.4 +/- 15.5 mg. Despite elevated serum magnesium levels in all patients, the net daily removal was inadequate (31.2 +/- 15.5 mg). It was concluded that: (1) Unlike chronic hemodialysis, continuous ambulatory peritoneal dialysis removes significant amounts of parathyroid hormone. (2) Normal 25-(OH) vitamin D and vitamin D binding protein levels are maintained with continuous ambulatory peritoneal dialysis despite large protein losses. (3) Substantial amounts of phosphorus are removed with continuous ambulatory peritoneal dialysis but not to an extent that precludes use of phosphorus binders. (4) Dialysate containing lower magnesium and possibly higher calcium concentrations should be made available to improve mineral homeostasis.