“Biased” Comparison Between ANDY-Disc® and UltraBag® in Patients on CAPD

In their article, Wong et al1 failed to establish therapeutic equivalence of ANDY-Disc (Fresenius Medical Care, Bad Homburg, Germany) to UltraBag (Baxter, Deerfield, IL) regarding peritonitis. The study is inherently biased against the ANDY-Disc group, in having patients shifted from UltraSet (Baxter, Deerfield, IL) and needing transfer set change. The wash-in period of a month seems inadequate as most peritonitis episodes occurred during first half of study. Nonblinded studies cannot avoid bias.2 ANDY-Disc training methods are not specified. ANDY-Disc patients initiated totally new “connectology,” whereas a shift from UltraSet to UltraBag would have less difficulty and without transfer set change. The authors confess unreliable baseline data. There is lopsidedly high incidence of Staphylococcus coagulase–negative/Staphylococcus epidermidis peritonitis in the ANDY-Disc® group (14 versus 5 episodes). Authors attribute the higher incidence of peritonitis in the ANDY-Disc® group to product defects (which settled dramatically in last quarter). S epidermidis peritonitis is mild, easily treatable, and caused by touch contamination not product defects.3 Biofilms cause relapsing peritonitis necessitating catheter change.3 Did the authors follow this guideline? Disregard S epidermidis peritonitis, then the difference in peritonitis is not statistically significant. More realistic would be to follow-up for 2 years with a longer wash-in period or to compare patients starting 2 systems de novo as done earlier.4 This study showed similar peritonitis rates between the StaySafe double-bag disconnect system (Fresenius Medical Care, Bad Homburg, Germany) and UltraBag. StaySafe and ANDY-Disc are essentially similar except for the solution bag material. Our peritoneal dialysis center uses ANDY-Disc with peritonitis rates of 1 episode in 63.2 patient-months and low Gram-positive coccal peritonitis, suggesting good connectology.5, 6