The high rate of cardiovascular complications in the dialysis population cannot be explained by traditional cardiovascular risk factors. One of such factors proposed to contribute to the cardiovascular mortality in dialysis patient population is vascular calcification possibly resulting from disturbances of calcium-phosphate metabolism.

The aim of this study is to assess the effects of treatment with dialysate containing 1.75 or 1.5 mmol/L to 1.25 mmol/L calcium regarding coronary artery calcification and bone histomorphometry in hemodialysis patients.

Sample size calculations were based on previously reported changes in coronary artery calcification scores in hemodialysis patients during time (90% power with a two-sided, alpha error rate of 5%). Four hundred fifty-seven hemodialysis patients, taking drop-out rate into consideration, will be enrolled in this prospective-controlled study.The cases already being treated with calcium-based phosphate binder and dialysate containing 1.75 or 1.5 mmol/L calcium will be enrolled from eight hemodialysis centers.The cases will be randomized to two arms:

1. Dialysate containing 1.25 mmol/L calcium + calcium-based phosphate binder group: Dialysate calcium will be reduced from 1.75 or 1.5 mmol/L to 1.25 mmol/L in this group. Patients will use calcium-based phosphate binder according to phosphate level.
2. Dialysate containing 1.75 mmol/L calcium + calcium-based phosphate binder group (Control group): Dialysate calcium will remain or switched to 1.75 mmol/L and patients will be on calcium-based phosphate binder.

The study will last for 18 months.Coronary artery calcification (Multi-slice CT), bone histomorphometry, and bone mineral density will be assessed in the beginning and at the end of the study. Coronary artery calcification and bone mineral density will be measured in all patients; bone histomorphometry will be assessed in 150 patients, 75 from each group.

Inclusion Criteria:

• Aged between 18 and 80 years
• On maintenance bicarbonate hemodialysis scheduled thrice weekly, at least 12 hours/week
• To be treated with a dialysate containing 1.75 or 1.5 mmol/L calcium
• Willingness to participate in the study with a written informed consent

Exclusion Criteria:

• To be scheduled for living donor renal transplantation
• To have serious life-limiting co-morbid situations, namely active malignancy, active infection, end-stage cardiac, pulmonary, or hepatic disease
• Pregnancy or lactating
• To be unable to give informed consent because of mental incompetence or a psychiatric disorder
• To be on vitamin D treatment within six months of randomization or having iPTH values over target levels (>300 pg/mL)
• Hypercalcemia (Ca >10.5 mg/dl) with use of dialysate containing 1.75 or 1.5 mmol/L calcium