Relationship between the serum parathyroid hormone and magnesium levels in continuous ambulatory peritoneal dialysis (CAPD) patients using low-magnesium peritoneal dialysate

Cho, Min Seok; Lee, Kyun Sang; Lee, Youn Kyoung; Ma, Seong Kwon; Ko, Jeong Hee; Kim, Soo Wan; Kim, Nam Ho; Choi, Ki Chul

Abstract

BACKGROUND: One of the most common complications in patients with end stage renal disease is renal osteodystrophy and parathyroid hormone (PTH) plays a key role in the pathogenesis of renal osteodystrophy. It is known that patients undergoing CAPD (continuous ambulatory peritoneal dialysis) have increased risk of low turnover bone disease and relative hypoparathyroidism is related to its pathogenesis. Factors related to relative hypoparathyroidism are increased in extracellular calcium level, accumulation of aluminum, vitamin D treatment, good control of serum phosphate, diabetes mellitus, and old age. Recently it has been believed that magnesium plays an important role in regulating secretion of PTH. The aim of this study was to evaluate the relationship between serum PTH and serum magnesium as a factor increasing the frequency of relative hypoparathyroidism.
METHODS
Author studied 56 patients who had undergone CAPD for more than 6 months without any significant problems and had been followed by Chonnam National University Hospital. No patient had been previously treated with vitamin D or aluminum hydroxide. The patients had used peritoneal dialysate with the magnesium concentration of 0.5 mEq/L. Biochemical parameters were checked.
RESULTS
1. The mean serum magnesium level was 1.99+/-0.36 mEq/L. Among total 56 patients, 15 patients (26.8%) showed hypermagnesemia (serum magnesium > 2.2 mEq/L), and 5 patients (8.9%) showed hypomagnesemia (serum magnesium < 1.6 mEq/L)2. On all 56 patients, serum iPTH level was not correlated with serum magnesium level. But, it was inversely correlated with serum total calcium and ionized calcium levels, respectively (r=-0.365, p=0.006; r=-0.515 p<0.001).3. Among the 49 patients whose serum iPTH level was less than 300 pg/mL, serum iPTH level was inversely correlated with serum magnesium level (r=-0.295, p=0.039), and inversely correlated with serum total calcium and ionized calcium levels, respectively (r=-0.546, p<0.001; r=-0.572 p<0.001).4. Among the 49 patients whose serum iPTH level was less than 300 pg/mL, lower iPTH group (serum iPTH<120 pg/mL) showed higher serum magnesium level (p=0.037), higher serum total calcium level (p<0.001), and lower bone isoenzyme of alkaline phosphatase level (p<0.001) than those of higher iPTH group (120 pg/mL serum< or =iPTH<300 pg/mL).
CONCLUSION
Among the CAPD patients whose serum iPTH level was less than 300 pg/mL, there was a significantly inverse correlation between serum iPTH level and serum magnesium level. This study indicates that not only serum calcium level, but also serum magnesium level are important in the regulation of serum iPTH levels of CAPD patients who have been dialyzed by low-magnesium peritoneal dialysate.