On small solute clearance and patient outcomes: evidential practice or observational trepidation?

Recent guidelines on peritoneal dialysis adequacy set a minimum target for small solute clearance at Kt/V urea 1.70. While evidence from both observational studies and randomized controlled trials (RCTs) supports such a minimum target, there continues to be debate over what role small solute clearance plays in determining patient outcome. Current ANZDATA Registry results from Australia and New Zealand add fuel to this debate by demonstrating a significant nonlinear U-shaped relationship between peritoneal small solute clearance and patient survival. The ANZDATA results indicate that patients with too low or too high peritoneal Kt/V urea may be at significant risk of death compared to those with a peritoneal Kt/V urea between 1.70 and 2.00. As these results are somewhat at odds with results from published RCTs, we will examine the level of evidence from the observational setting that is the ANZDATA Registry and contrast it against the level of evidence from RCTs, particularly the ADEMEX trial. New results from the ADEMEX study are presented as a possible explanation for the paradoxical U-shaped results seen in the ANZDATA study.