Paired Donor Kidneys: Graft and Patient Survival Diverge

Key Takeaways

• Among U.S. recipients of contralateral deceased-donor kidneys, death-censored kidney graft survival was higher for adult SPK recipients than for pediatric kidney-alone recipients.
• Pediatric kidney-alone recipients had higher patient survival than adult SPK recipients.
• Freedom from graft failure or death did not differ significantly between the recipient groups.

Allocating deceased-donor kidneys between adult simultaneous pancreas–kidney and pediatric kidney-alone candidates raises a question about kidney-graft longevity and recipient survival. Neither endpoint captures both outcomes. Comparing kidneys from the same donor allows investigators to examine each under a shared donor background.

Investigators used data from the United States Scientific Registry of Transplant Recipients (SRTR) for a retrospective paired-donor analysis. They identified 1,675 deceased donors whose contralateral kidneys went to an adult simultaneous pancreas–kidney (SPK) recipient and a pediatric kidney-alone (KI) recipient between 2010 and 2025. The outcomes were death-censored kidney graft survival, patient survival, and freedom from the composite of graft failure or death. Investigators used Kaplan–Meier estimates at prespecified landmarks through 10 years and log-rank comparisons. Pairing kidneys accounts for donor characteristics, but does not make the adult and pediatric recipients alike.

At 10 years, death-censored kidney graft survival was 82.1% among adult SPK recipients versus 70.6% among pediatric KI recipients. Patient survival favored the other group: 95.4% of pediatric KI recipients versus 78.3% of adult SPK recipients were alive at that point. Both comparisons were statistically significant.

Freedom from either graft failure or death at 10 years was 69.1% in adult SPK recipients versus 67.9% in pediatric KI recipients. This composite outcome did not differ significantly between groups (log-rank p = 0.47).

Pairing kidneys reduces donor-level confounding, but these observed outcomes do not establish what would happen if an organ were assigned to a different recipient group. Retrospective registry data cannot fully capture recipient comorbidity and adherence, differences in center practices and immunosuppression, or transition readiness and social determinants. They also cannot fully identify mechanisms of graft loss. These limits prevent the group differences from being interpreted as effects of an allocation choice.

For the authors, graft longevity and recipient survival remain competing considerations alongside the comparable composite outcome. This observational comparison does not identify an optimal deceased-donor kidney allocation policy.

Clinician Questions

How does death-censored graft survival differ from graft-failure-or-death survival for adult SPK and pediatric kidney-alone recipients?

Death-censored graft survival considers kidney graft longevity with recipient deaths censored. Freedom from graft failure or death instead treats either event as part of the combined outcome, so the measures capture different events.

Did the paired-kidney analysis establish why graft and patient outcomes diverged between pediatric kidney-alone and adult SPK recipients?

No. Rao and colleagues proposed pediatric developmental, adherence, psychosocial, and transition-of-care challenges as possible contributors to kidney graft outcomes, and the comorbidity burden of longstanding diabetes as a possible contributor to mortality among adult SPK recipients. These were hypotheses, not demonstrated explanations; the registry comparison cannot identify the causal pathways.