Importance: Lengthening waiting lists for organ transplantation mandate development of strategies to expand the deceased donor pool. Due to concerns regarding organ viability, most organ donation organisations internationally “stand-down” from potential circulatory death donors (DCD) after 1-2 hours, possibly underutilising an important organ source. UK policy mandates a minimum 3-hour stand-down time. Objective: To determine whether time to death (TTD, also termed “agonal time”) from withdrawal of life-sustaining-treatment (WLST) is an important predictor of kidney transplant outcome. Design: Population-cohort study from 2013-2021 with follow-up until October 2023. Setting: All 23 UK kidney transplant centres, using data from the prospectively maintained UK Transplant Registry. Participants: Adult recipients of DCD kidney-alone transplants. Exposure: Duration of TTD defined as time from WLST to donor mechanical asystole. Main outcomes and measures: Primary outcome was 12-month eGFR, with secondary outcomes of delayed graft function and graft survival (censored at death or 5 years). Results: This study included 7,183 kidney transplant recipients (65% male). Median (IQR) donor and recipient age was 55 (44-63) and 56 (47-64) years. TTD median (range) was 15 (0-407) minutes, with 885 and 303 kidneys transplanted from donors with TTD over 1 and 2 hours respectively. Donor TTD was not associated with recipient 12-month eGFR on adjusted linear regression (change per doubling of TTD = -0.25, 95% CI -0.68 to 0.19, P=0.27), nor with delayed graft function (aOR=1.01; 95% CI 0.97-1.06, P=0.65) or graft survival (aHR=1.00; 95% CI, 0.95-1.07, P=0.92). These findings were confirmed with restricted cubic spline models (assessing non-linear relationships) and tests of interaction (including normothermic regional perfusion, donor age, ischemic times). In contrast, donor asystolic time, cold ischemic time, and reperfusion time were independent predictors of outcome. Compared to theoretical 1- or 2-hour stand-down times, UK policy (minimum 3-hour wait to stand-down) has led to 14.1% and 4.4% more DCD transplants, respectively. Conclusions and relevance: In this cohort study of DCD kidney recipients, donor TTD did not impact on post-transplant outcome, in contrast to subsequent ischemic times. Altering international transplant practice to mandate minimum 3-hour donor stand-down times would substantially increase numbers of kidney transplants performed without prejudicing outcomes
