The KDIGO guideline for dialysate calcium will result in an increased incidence of calcium accumulation in hemodialysis patients

The recently published KDIGO (Kidney Disease: Improvement of Global Outcomes) guideline (GL) for dialysate calcium suggests a narrow range of dialysate inlet calcium concentrations (CdiCa++) of 2.50–3.00 mEq/l. The work group's primary arguments supporting the GL were (1) there is a negligible flux of body Ca++ during dialysis and (2) CdiCa++ of 2.50 mEq/l will generally result in neutral Ca++ mass balance (CaMB). We believe we have shown that both of these arguments are incorrect. Kinetic modeling and analysis of dialyzer Ca++ transport during dialysis (JdCa++) demonstrates that more than 500 mg of Ca can be transferred during a single dialysis and that on average 76% of this Ca flux is from the miscible calcium pool rather than plasma pool. Kinetic modeling of intestinal calcium absorption (CaAbs) shows a strong dependence of CaAbs on the dose of vitamin D analogs and weaker dependence on the level of Ca intake (CaINT). We used the CaAbs model to calculate CaAbs as a function of total CaINT and prescribed doses of vitamin D analogs in 320 hemodialysis patients. We then calculated total dialyzer calcium removal (TJdCa++) and the CdiCa++ that would be required to achieve TJdCa++=CaAbs, that is, CaMB=0 over the whole dialysis cycle (that is, covering both the intra- and the inter-dialytic period). The results indicate that 70% of patients on Ca-based binders and 20–50% of patients on non-Ca-based binders would require CdiCa++ <2.50 mEq/l to prevent long-term Ca accumulation.