US Population Size and Outcomes of Adults on Liver Transplant Waiting Lists.

Importance: Disparities in organ supply and demand led to geographic inequities in the score-based liver transplant (LT) allocation system, prompting a change to allocation based on acuity circles (AC) defined by fixed distances. However, fixed distances do not ensure equivalent population size, potentially creating new sources of disparity. Objective: To estimate the association between population size around LT centers and waiting list outcomes for critically ill patients with chronic end-stage liver disease and high Model for End-stage Liver Disease (MELD) scores or acute liver failure (ALF). Design, Setting, and Participants: This US nationwide retrospective cohort study included adult (aged ≥18 years) candidates for deceased donor LT wait-listed between June 18, 2013, and May 31, 2023. Follow-up was completed June 30, 2023. Participants were divided into pre-AC and post-AC groups. Exposure: Population size within defined radii around each LT center (150 nautical miles [nm] for participants with high MELD scores and 500 nm for those with ALF) based on AC allocation policy. Main Outcomes and Measures: LT candidate waiting list mortality and dropout rate were analyzed using generalized linear mixed-effect models with random intercepts for center and listing date before and after AC implementation. Fine-Gray competing risk regression, accounting for clustering, was used as a secondary model. Results: The study analyzed 6142 LT candidates (1581 with ALF and 4561 with high MELD scores) during the pre-AC era and 4344 candidates (749 with ALF and 3595 with high- MELD scores) in the post-AC era, for a total of 10 486 participants (6331 male [60.5%]; mean [SD] age, 48.5 [7.1] years). In the high-MELD cohort, being listed at a center in the lowest tertile of population size was associated with increased waiting list mortality in the AC era (adjusted odds ratio [AOR], 1.68; 95% CI, 1.14-2.46). Doubling of the population size was associated with a 34% reduction in the odds of mortality or dropout (AOR, 0.66; 95% CI, 0.49-0.90). These results were consistent with those of the extended Fine-Gray models and were also corroborated by multiple sensitivity analyses. However, there were no significant population density-associated disparities in the ALF cohort. Conclusions and Relevance: In this retrospective nationwide cohort study, being wait-listed in less populated regions was associated with greater mortality among critically ill LT candidates with high MELD scores, underscoring the limitations of allocation systems based purely on fixed distances.