BackgroundAlthough hyperphosphatemia is one of the few established risk factors for cardiovascular mortality in patients on dialysis, the relationship between peritoneal dialysis (PD) prescription and dialytic phosphate removal is largely unexplored.Methods and PatientsWe analyzed 24-hour clearances ( n = 60) together with peritoneal equilibration tests (PETs) ( n = 52) performed in children and adolescents ( n = 35) on automated PD.ResultsDialytic phosphate clearance was more closely correlated with 2-hour and 4-hour dialysate-to-plasma ratio (D/P) of phosphate in the PETs ( r = 0.44 and r = 0.52, both p < 0.0001) than with 2-hour and 4-hour D/P creatinine ( r = 0.26 and r = 0.27, both p < 0.05). Dialytic 24-hour phosphate clearance was independently predicted by total fluid turnover (partial R²= 0.48, p < 0.001), the number of cycles ( r = 0.52, p < 0.001), 2-hour D/P phosphate (partial R²= 0.07, p = 0.001), dwell time (partial R²= 0.05, p = 0.01), and achieved ultrafiltration (partial R²= 0.05, p = 0.005). 4-hour D/P phosphate and 24-hour phosphate clearance were significantly lower in hyperphosphatemic children (3.38 ± 1.17 vs 4.56 ± 1.99 L/1.73 m²/day, p < 0.05), whereas creatinine equilibration and clearance rates were not distinctive.ConclusionDialytic phosphate removal is an important modifiable determinant of phosphate control in automated PD. It strongly depends on total dialysate turnover and the prescribed number of cycles and is more adequately predicted by phosphate than by creatinine equilibration characteristics. Due to the deleterious effects of hyperphosphatemia, dialytic phosphate removal should be monitored routinely.