Simplified phosphorus kinetic modeling: predicting changes in predialysis serum phosphorus concentration after altering the hemodialysis prescription.

BACKGROUND The KDIGO work group recommends increasing dialytic phosphorus removal in Stage 5D chronic kidney disease patients with persistent hyperphosphatemia; however, optimal prescriptions to enhance phosphorus removal by hemodialysis (HD) therapies have not yet been established. This study evaluated whether phosphorus kinetic modeling based on a pseudo one-compartment model could provide practical clinical guidance for predicting changes in predialysis serum phosphorus concentration after altering the HD prescription. METHODS Patient-specific phosphorus kinetic parameters determined from thrice weekly HD treatments on 774 patients in the HEMO Study were used to predict changes in predialysis serum phosphorus concentration after altering the HD prescription from thrice weekly to short daily and long nocturnal HD therapies. The effect of changes in the oral phosphorus binder prescription on predicted changes in the predialysis serum phosphorus concentration was also illustrated using the concept of equivalent phosphorus binder dose. RESULTS Decreases in predialysis serum phosphorus concentration from thrice weekly HD to short daily and long nocturnal HD prescriptions demonstrated strong associations with the predialysis serum phosphorus concentration during thrice weekly HD that were relatively independent of patient-specific phosphorus kinetic parameters. Thus, the percent decrease in predialysis serum phosphorus concentration was approximately the same among patients for a given alteration in the HD prescription. Both increased weekly treatment time and frequency resulted in a reduction in the predialysis serum phosphorus concentration; however, the effect of treatment time was more influential. Simultaneous reduction in the effective phosphorus binder dose blunted the decrease in the predialysis serum phosphorus concentration. CONCLUSIONS This study demonstrated that a simplified form of phosphorus kinetic modeling based on a pseudo one-compartment model can provide practical clinical guidance for predicting changes in predialysis serum phosphorus concentration after altering the HD prescription. Prospective validation of this approach in future studies is warranted.