Serum osteoprotegrin level is lower in peritoneal dialysis patients than in hemodialysis ones
Grzegorzewska AE, Mlot M

Purpose: Osteoprotegrin (OPG) and OPG-ligand are involved in bone turnover induced by parathyroid hormone (PTH) in renal osteodystrophy. We determined serum OPG level in dialysis patients and checked its correlations with other parameters of bone turnover. 
Material and methods: Serum level of OPG, PTH, phosphates (Pi), calcium, total alkaline phosphatase (AP) and pH was determined in 29 peritoneal dialysis (PD) patients and 41 hemodialysis (HD) ones.
Results: OPG level was lower in PD than HD patients (4.0, 2.1-13.4 pmol/L vs 7.9, 0.9-16.5 pmol/L; p=0.000) and in both groups it was higher than in controls (2.2, 1.0-3.9 pmol/L; p=0.000). PD patients had also lower AP (78.0, 34.0-583.0 U/L vs 116.0, 59.0-577.0 U/L; p=0.000) and Pi (1.4±0.4 mmol/L vs 3.4±2.6 mmol/L; p=0.000) than HD patients, but higher calcium level (2.4±0.2 mmol/L vs 2.2±0.3 mmol/L; p=0.002) and pH (7.412±0.051 vs 7.326±0.043; p=0.000). The only correlation displayed in PD patients for OPG was negative one with pH (r=-0.417, p=0.038) and in HD patients – positive with Pi (r=0.548, p=0.000). OPG level was elevated in 38 HD (92,7%) and in 15 PD (51,7%) patients. There was correlation between serum OPG and AP (r=-0.615, p=0.033) and calcium (r=0.575, p=0.040) in group characterised by normal OPG value. There were no significant correlations in group with elevated OPG level. 
Conclusions: Lower serum OPG level in PD patients may be connected with lower activity of osteoclasts and less compensating production of OPG in this group of patients. Lower serum OPG level may contribute to higher serum calcium level in PD patients.

Kay words:   osteoprotegrin, parathormone, peritoneal dialysis, hemodialysis.