Inverse correlation between serum magnesium and parathyroid hormone in peritoneal dialysis patients: a contributing factor to adynamic bone disease?

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Secondary hyperparathyroidism (SHPTH) is present in many patients with end-stage renal disease (ESRD) and has been linked to uremic bone disease. Parathyroid hormone (PTH) levels are affected by calcium, vitamin D, and phosphorus. Recent data suggests that serum magnesium may also modulate PTH levels. The aim of this retrospective study was to investigate the impact of different calcium (Ca) and magnesium (Mg) concentrations of dialysis solutions on serum Mg and serum PTH levels in peritoneal dialysis (PD) patients. Two groups of PD patients-group A (n = 17) on "standard" Ca and Mg dialysis solution (SCa-MgD) (Ca: 1.62 mmol/l, Mg: 0.75 mmol/l and Lactate 35 mmol/l), and group B (n = 29) on "low" Ca and Mg dialysis solution (LCa-MgD) (Ca: 1.25 mmol/l, Mg: 0.25 mmol/l and Lactate 40 mmol/l), on PD for more than 6 months, were studied. Calcium carbonate (CaCO3) was used as the phosphate (P) binder in 87% (40/46) of the patients. Biochemical parameters were evaluated every 1-2 months over 6 months and the mean values were computed. No significant differences were found between the two groups in all parameters except for serum Mg and PTH. Serum Mg was higher in SCa-MgD group compared to those in the LCa-MgD group (1.05 +/- 0.19 vs 0.90 +/- 0.23 mmol/l, respectively) and serum PTH was higher in LCa-MgD group compared to those in SCa-MgD group (72.3 +/- 64.2 vs 31.1 +/- 39.0 pmol/l, respectively) even though serum Ca was not different. There was a statistically significant inverse correlation between serum Mg and PTH levels (r = -0.357, p < 0.05). Serum Mg is lower and serum PTH higher in patients dialyzed with lower Mg concentration dialysis solution compared to those with higher Mg concentration dialysis solution. Our study confirms previous reports that serum Mg may have a suppressive role on PTH synthesis and/or secretion, and thus may play a role in pathogenesis of adynamic bone disease that often develops in patients on chronic PD with high calcium and high magnesium concentrations.