- The study investigated if transplant center location impacts donor lung availability and how an amended Composite Allocation Score (CAS) policy affects candidate prioritization.
- Researchers conducted a retrospective cohort study using Scientific Registry of Transplant Recipients data from 3917 candidates across 61 centers.
- Median center-level distance-adjusted donor availability was 1.90 donors per candidate-day, with 23.9% of top-ranked candidates deprioritized under the amended policy.
- The authors concluded that increasing proximity's influence in the amended CAS policy reduces effective donor availability and increases geographic disparities.
- This suggests that the amended policy may worsen access for harder-to-match candidates, particularly those with blood type O, requiring careful consideration.
Navigating Geographic Disparities in Lung Transplant Access
For patients with end-stage lung disease, transplantation is a critical, life-extending intervention, yet access to donor organs remains a complex challenge [1]. While disparities in healthcare access are a global concern tied to factors like socioeconomic status and regional infrastructure [2, 3, 4], organ allocation is unique in that it is governed by explicit policies that directly determine a patient's chance of receiving a transplant [5]. For clinicians managing these vulnerable patients, understanding the nuances of these policies is essential for counseling and prognosis [6]. A recent retrospective study now provides a quantitative analysis of how the latest U.S. lung allocation policies affect geographic equity and patient prioritization.
Evolution of Lung Allocation Policy and Study Design
The U.S. lung allocation system has long aimed for geographic equity. In a significant move in March 2023, the policy shifted from rigid distance cutoffs to a continuous distribution framework using the Composite Allocation Score (CAS). This score integrates a patient's medical urgency, projected posttransplant survival, and biological compatibility with a factor for geographic efficiency, which is a continuous function of the distance between donor and candidate. A further amendment, approved for May 7, 2026, is set to increase the weight of this proximity factor. To understand the real-world effects of these policies, researchers conducted a retrospective cohort study using data from the Scientific Registry of Transplant Recipients. The analysis included all adult lung transplant candidates, recipients, and donors from September 27, 2023, to December 1, 2024. The primary outcome was distance-adjusted donor availability, a metric defined as the number of biologically compatible donors recovered within 30 days of a candidate's listing, weighted by the CAS geographic formula. The team used spatial regression, a statistical method for analyzing geographic patterns, to map variations across transplant centers. To predict the impact of the future policy, they ran "what-if" scenarios, known as counterfactual analyses, and performed match-run analyses to simulate how the new rules would re-rank specific candidates for available organs.
Baseline Donor Availability and Geographic Variation
The study first quantified donor availability under the current continuous distribution framework. Among a cohort of 3,917 candidates across 61 transplant centers, the median center-level distance-adjusted donor availability was 1.90 donors per candidate-day (IQR, 1.75-2.14). This metric reflects the pool of geographically weighted, biologically compatible donors available to a patient. However, this median value concealed a critical finding: the study uncovered substantial variation in donor availability across different centers and regions. This means that even under the current system, a patient's access to a donor lung is significantly influenced by where they are listed for transplant. To confirm this was not due to other factors, the researchers adjusted for center size and the candidates' biological characteristics. Even after these adjustments, a transplant center's location remained significantly associated with donor availability. This finding establishes that geographic inequity is a persistent feature of the lung allocation landscape, creating inherent disadvantages for patients listed at centers in certain locations.
Impact of Increased Proximity on Access and Prioritization
The study's projections for the upcoming May 7, 2026, policy amendment raise significant concerns. The counterfactual analyses, which simulated the effects of giving more weight to donor-candidate proximity, predicted that the new policy would reduce overall effective donor availability and increase geographic disparities in access. This suggests the policy intended to improve local efficiency may inadvertently shrink the accessible organ pool for many and worsen the very inequities it sought to address. The impact on individual patients was starkly illustrated in the match-run analyses. The simulation showed that 23.9% of candidates who were ranked in the top 10 for an organ under the current CAS policy would be displaced from that top-10 position under the amended policy. This represents a substantial reordering of the waitlist. Critically, this de-prioritization disproportionately affected patients with existing biological barriers to matching. The study specifically notes that candidates with blood type O, who as universal donors can only receive from other type O donors, experienced greater de-prioritization. For clinicians, this finding signals that the upcoming policy change could create additional hurdles for harder-to-match patients, potentially prolonging their wait times and complicating their management.
Persistent Disparities and Clinical Implications
This large retrospective cohort study confirms that significant geographic variation in effective donor availability persists under the current Composite Allocation Score (CAS) policies. The analysis of 3,917 candidates demonstrated that a patient's transplant center location is a powerful determinant of their access to a donor organ, independent of center volume or patient-specific biological factors. This finding highlights that the 2023 policy shift to a continuous distribution model did not eliminate geographic inequity. More concerning for future practice, the study's simulations project that the upcoming May 7, 2026, policy amendment may increase these geographic disparities. By increasing the influence of donor-candidate proximity, the new rules are predicted to de-prioritize a significant portion of candidates, particularly those who are already harder-to-match, such as individuals with blood type O. For practicing physicians, these findings are a crucial alert. They underscore the need to counsel patients about how evolving allocation policies may affect their waitlist status and prognosis. Furthermore, they highlight the ongoing tension between organ distribution efficiency and the principle of equitable access, suggesting that clinicians have a vital role in advocating for policies that do not inadvertently penalize patients based on their location or biological profile.
References
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