The purpose of this study is to investigate the effectiveness of using two dialysers to lower the blood mineral levels in people receiving hemodialysis as compared to using one dialyser (usual treatment).

Higher levels of serum phosphate are independently associated with an increased risk of death in hemodialysis patients. Therefore, there has been considerable interest in controlling serum phosphate while minimizing oral calcium load. While most attention has focused on the use of non-calcium containing phosphate binders such as sevelamer and lanthanum, modifying conventional dialysis regimens to improve phosphate clearance is an alternative approach that remains relatively unstudied. A secondary analysis of a previous randomized cross-over study from our group found that the use of two dialysers in parallel resulted in a reduction in pre-dialysis serum phosphate levels. As this study was small, and the mechanisms resulting in the reduction in phosphate levels were unclear, further study is warranted. The investigators will conduct a randomized cross-over study comparing the impact of dialyzing using two dialysers in parallel with a single dialyser in hyperphosphatemic hemodialysis patients.

There will be a total of 34 participants from Alberta,Canada participating in this study. The length of study participation is 10 weeks.

Inclusion Criteria:

• Age > 18 years
• Patients must be on a stable regimen of hemodialysis for ≥ 3 months ('stable' defined as not expected to require a change to the duration or frequency of treatments)
• Serum phosphate > 1.6 mmol/l on last two consecutive lab tests at least 3 weeks apart (KDOQI guidelines recommend maintaining predialysis phosphate < 1.8mmol/l - as such, phosphate lowering in this subgroup of patients is particularly relevant)
• Patients must be on stable doses of a phosphate binder with no changes in dose 1 month prior to study enrolment.
• Blood flow rate ≥ 350 ml/min through a well-functioning access (This will exclude patients receiving inadequate dialysis due to a temporary venous dialysis catheter and will ensure sufficient blood flow to permit dialysis using two dialysers in parallel.)

Exclusion Criteria:

• Patients who have a scheduled renal transplant, change in dialysis modality, surgery or hospitalization or plan on moving away from the study site in the next three months.
• Patients with a projected life expectancy of less than 3 months.
• Patients with a contraindication to intra-dialytic anticoagulation. (Some patients require a small increase in the amount of anticoagulation required to prevent dialyser clotting when using two dialysers in parallel).
• Patients who have missed >8 dialysis treatments in the past 3 months.
• Patients with a dialysis regimen of >3 runs per week.
• Failure to provide informed consent.
• Patients enrolled in another (interventional) trial