Are peritoneal dialysis patients with and without residual renal function equivalent for survival study? Insight from a retrospective review of the cause of death

Background. It remains unknown whether results of survival studies in anuric patients can be extrapolated to those who still have significant urine output. It is possible that after a prolonged period on dialysis, anuric patients are qualitatively different from patients with residual renal function. Methods. We performed a retrospective review to study the cause of death of 296 peritoneal dialysis patients of our centre over a 7 year period, and compared the mortality and distribution of cause of death between patients with and without residual renal function. Results.. One hundred and forty-two cases (48.0%) died of vascular diseases, 82 cases (27.7%) died of infections and 72 cases (24.3%) died of other causes. Anuric patients had a higher overall mortality rate than non-anuric patients (14.9 vs 9.9%, P=0.0005), and the difference was almost completely attributed to the difference in mortality from vascular diseases (8.0 vs 4.1%, P<0.0001). Vascular disease was a more common cause of death in anuric patients than those with residual renal function (55.3 vs 40.8%, P=0.011). The difference was largely explained by the higher prevalence of sudden cardiac death in anuric patients (39 in 149 vs 19 in 147 cases). Patients without preexisting cardiovascular disease more commonly died of vascular disease after they became anuric (47.4 vs 34.0%, P=0.017). The difference could not be explained by the longer duration of dialysis in anuric patients because there was no significant change in the distribution of cause of death with time on dialysis (chi-square test, P=0.341). Conclusions. Our observation suggests that peritoneal dialysis patients with and without residual renal function are qualitatively different. Studies on peritoneal dialysis adequacy and survival in anuric patients should only be extrapolated to the general dialysis population with caution.