Cold ischemia time and outcomes after deceased donor kidney transplantation: a nationwide Thai registry and paired-kidney analysis

Prolonged cold ischemia time (CIT) is associated with delayed graft function (DGF), but its impact on long-term outcomes remains uncertain in Asian deceased donor kidney transplantation (DDKT) systems. We conducted a nationwide study of all DDKTs performed in Thailand from 2001 to 2019. Associations between CIT and DGF, overall transplant failure, death-censored graft failure (DCGF), and patient mortality were evaluated using multivariable regression models; paired-kidney analyses minimized donor-level confounding. Among 4,603 DDKTs from 2,449 donors, median follow-up was 70.5 months. Mean CIT was 19.0 ± 5.4 h. DGF increased progressively from 28.9% with CIT ≤ 12 h to 63.2% with CIT > 30 h. Each 1-hour CIT increase was independently associated with DGF (adjusted OR 1.07, 95% CI 1.06–1.08), overall transplant failure (adjusted HR 1.021, 95% CI 1.011–1.030), DCGF (adjusted HR 1.024, 95% CI 1.011–1.037), and patient mortality (adjusted HR 1.023, 95% CI 1.010–1.036). RCS analysis confirmed a significant non-linear association between CIT and DGF ( P = 0.0008), with risk relatively stable below ~ 12–14 h before rising sharply to 22 h. CIT > 14 h was the lowest threshold associated with worse graft outcomes. In paired-kidney analyses, the longer-CIT kidney had higher risks of overall transplant failure (adjusted HR 1.192, 95% CI 1.048–1.357) and DCGF (adjusted HR 1.268, 95% CI 1.064–1.512). A paired-kidney CIT difference (ΔCIT) > 2 h provided the strongest separation for long-term graft outcomes. CIT was associated with adverse early and long-term outcomes after DDKT. Shortening CIT to below 14 h, ideally toward 12 h when feasible, and minimizing ΔCIT to within 2 h may serve as pragmatic system-level targets, rather than criteria for organ discard.