Differences in calcium kinetic pattern between CAPD and HD patients.

To assess the effect of different dialysis modalities on calcium turnover, we studied 57 patients on maintenance hemodialysis treatment (HD) and 38 patients on continuous ambulatory peritoneal dialysis (CAPD) with tracer kinetic studies using two calcium isotopes (45Ca by mouth and 47Ca intravenously). The two groups were comparable in age, sex and prevalence of diabetes. The groups did not differ in their serum concentrations of intact parathyroid hormone (iPTH), calcium, inorganic phosphate and 1,25-dihydroxyvitamin D. 25-hydroxy-vitamin D and alkaline phosphatase were found to be significantly higher in HD patients. Despite these similarities, CAPD patients showed a significantly lower calcium kinetic response as measured by calcium retention and plasma calcium efflux than HD patients. Mean calcium retention was 39.5% in HD patients compared to 31.2% in the CAPD group (p < 0.05). Plasma calcium efflux was significantly lower in the CAPD group (2.7 vs 3.2 respectively; p < 0.01). iPTH correlated with calcium retention and plasma calcium efflux in HD patients (r = 0.69 and r = 0.67 respectively). In CAPD patients, the correlation coefficient between iPTH and calcium retention was markedly lower (r = 0.54), whereas no correlation was found between iPTH and plasma calcium efflux (r = 0.08). In addition, the slope of the correlation curve were higher in HD patients (p < 0.01 and p < 0.001, respectively), indicating a better response of this patient group to the action of parathyroid hormone. Our data are in accordance with recently published results showing that the dialysis modality has a major impact on bone turnover and on the progression of uremic bone disease. It has been shown that CAPD is an independent risk factor for the development of the adynamic form of renal bone disease. This finding may be explained by the lower response of calcium turnover to the action of PTH as shown here with tracer kinetic studies.