Long-Term Mortality and Causes of Death After Kidney and Liver Transplantation: A Nationwide Population-Based Cohort Study in South Korea

Background/Objectives: We analyzed long-term and cause-specific mortality among kidney and liver transplant recipients in South Korea. Methods: Using National Health Insurance Service and Statistics Korea data, we identified 24,332 kidney and 16,325 liver transplant recipients transplanted between 2006 and 2020. Three-, five-, and ten-year survival rates were estimated in nested fixed-entry subcohorts with observation closed at each horizon; multivariable Cox models were fitted in the full cohorts, with subcohort models used as consistency checks. Standardized mortality ratios (SMRs) applied identical cause-of-death classifications to observed and expected deaths (2011–2020). Results: Kidney recipient survival was 96.22% (95% CI 95.94–96.50), 94.53% (94.15–94.91), and 90.11% (89.31–90.92) at 3, 5, and 10 years, respectively; liver recipient survival was 81.28% (80.59–81.97), 78.27% (77.44–79.10), and 72.41% (71.02–73.80), respectively. Renal disease was the leading cause of death in kidney recipients (31.62%) and hepatic malignancy in liver recipients (42.35%). Male sex, older age, and lower income were associated with higher mortality in both cohorts; living-donor transplantation was associated with lower mortality than deceased-donor transplantation (hazard ratio [HR] 0.54; 0.50–0.58). Mortality was 3.65-fold and 7.58-fold that of the general population in kidney and liver recipients, respectively. Infection-related SMRs declined over time in both cohorts, whereas the suicide-related SMR among liver transplant recipients increased more than fourfold. Conclusions: Transplant recipients bear a substantially higher mortality burden than the general population, and the leading causes of death differ by transplanted organ and change over time. These findings support continued surveillance for malignancy, metabolic complications, and mental health.