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Differences in calcium kinetic pattern between CAPD and HD patients
1St. Markus Hospital, Frankfurt/M, Germany.
Insights
Continuous ambulatory peritoneal dialysis (CAPD) patients show a reduced calcium turnover response compared to hemodialysis (HD) patients, impacting bone disease progression. This suggests dialysis modality significantly affects calcium metabolism and bone health in patients with kidney disease.
Area of Science:
- Nephrology
- Mineral Metabolism
- Bone Biology
Background:
- Dialysis modalities significantly impact mineral metabolism and bone health in patients with chronic kidney disease.
- Understanding calcium turnover differences between hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) is crucial for managing uremic bone disease.
Purpose of the Study:
- To compare calcium turnover kinetics between patients undergoing maintenance hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD).
- To investigate the relationship between parathyroid hormone (PTH) and calcium kinetics in different dialysis modalities.
Main Methods:
- Tracer kinetic studies using two calcium isotopes (45Ca orally, 47Ca intravenously) were performed on 57 HD patients and 38 CAPD patients.
- Serum levels of intact parathyroid hormone (iPTH), calcium, phosphate, and vitamin D metabolites were measured.
- Calcium retention and plasma calcium efflux were quantified to assess calcium turnover.
Main Results:
- CAPD patients exhibited significantly lower calcium retention (31.2% vs 39.5% in HD) and plasma calcium efflux (2.7 vs 3.2 in HD).
- While iPTH levels were similar, HD patients showed a stronger correlation between iPTH and calcium kinetics, indicating a better PTH response.
- HD patients had higher 25-hydroxy-vitamin D and alkaline phosphatase levels compared to CAPD patients.
Conclusions:
- Dialysis modality critically influences calcium turnover and bone metabolism.
- CAPD is associated with a diminished calcium kinetic response to PTH, potentially contributing to the adynamic bone disease observed in these patients.
- These findings highlight the importance of considering dialysis modality when managing bone complications in chronic kidney disease.
Abstract:
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.