An instrumental variable approach confirms that the duration of pretransplant dialysis has a negative impact on the survival of kidney transplant recipients and quantifies the risk.

Dialysis prior to kidney transplantation may have a detrimental effect on post-transplant outcomes. However, prior studies have not fully characterized the nature of this relationship and may have been subject to residual confounding. Here we investigated the association between pre-transplant dialysis duration and two post-transplant outcomes: all-cause death and death with functioning graft. This was a retrospective, population-based, cohort study in all deceased donor kidney transplants performed in Ontario, Canada, from April 1, 2002 to March 31, 2013. Patient blood type was chosen as an instrumental variable and a two-stage modeling procedure that included a threshold-adjusted Cox proportional hazards model was used to assess the association between dialysis time and the two post-transplant outcomes. Among 4,440 transplant recipients, the relative risk of all-cause death associated with each dialysis year prior to three years was 42% and fell to 5% per additional dialysis year thereafter. For death with functioning graft, each dialysis year before and after 2.8 years increased the relative risk by 31% and 4%, respectively. Peak panel reactive antibody of more than 50% was independently associated with an elevated risk of death with functioning graft but not with the risk of all-cause death. Thus, our findings highlight the urgency to develop strategies to ensure timely transplant listing and to shorten the total dialysis time before transplantation, with the goal of enhancing kidney transplant outcomes.