A new lung allocation system that prioritizes medical urgency has achieved a dramatic 75% reduction in waitlist deaths since its implementation in March 2023, according to research presented at the American Thoracic Society's international conference in San Francisco.
The study, led by Dr. Mary Raddawi from Columbia University Irving Medical Center, analyzed outcomes for 24,368 patients listed for lung transplantation since February 2015, revealing that patients are now three times less likely to die while waiting for donor organs compared to the previous geographic proximity-based system.
Transforming Organ Allocation Through Medical Priority
The United Network for Organ Sharing (UNOS) Composite Allocation Score (CAS) represents a fundamental shift in how donor lungs are distributed across the United States. Prior to November 2017, organs were allocated primarily based on geographic proximity to the donor, meaning patients living closer to donation sites received priority regardless of their medical condition.
"We always want to make sure that any time we make a change to the allocation system that we're improving outcomes, especially for our sickest patients," said Dr. Raddawi, a second-year pulmonary and critical care fellow. "This provides confirmation that we're on the right track."
The transformation occurred in two phases. Following a 2017 lawsuit, the allocation radius expanded from local areas to 250 nautical miles, broadening access to donor organs. Then in March 2023, UNOS implemented the CAS system, which considers multiple factors including medical urgency, blood type compatibility, and geographic distance.
Dramatic Mortality Reductions Across Patient Populations
The retrospective cohort study divided patients into three distinct eras, revealing progressive improvements in waitlist outcomes. Overall mortality rates dropped from 11.2% in the pre-2017 era to 8.4% after geographic expansion, and further declined to 4.1% following CAS implementation.
The most critically ill patients experienced the greatest benefit. Among those in the top 5% of medical urgency scores at listing, mortality plummeted from 34.5% in the pre-2017 era to 22.2% after geographic expansion, and ultimately to just 6.5% under the current CAS system.
Patients requiring high-flow nasal cannula support at listing showed similarly dramatic improvements, with adjusted hazard ratios indicating 7.68-fold and 5.28-fold increased risks of death in the earlier eras compared to the CAS period.
Statistical Significance and Clinical Impact
In adjusted models accounting for patient characteristics and disease severity, the pre-2017 and post-2017 eras were associated with 3.3-fold and 2.1-fold increased risks of death or delisting compared to the CAS era (P <.001 for both comparisons). For the sickest patients, these risks were even more pronounced, with 8-fold and 4.8-fold increased mortality risks in the earlier periods.
"When you think about the fact that now we're focusing on many different factors, including medical urgency, it makes sense that the waitlist mortality would go down for our sicker patients — but it is nice to see the actual numbers," Raddawi explained.
Implications for Clinical Practice
The findings underscore the importance of accurate medical urgency assessment and physician advocacy for critically ill patients. The CAS system's success in reducing mortality highlights how evidence-based allocation policies can translate into meaningful clinical outcomes.
The research team plans to conduct more detailed analyses to identify which specific factors within the CAS scoring system contribute most significantly to improved outcomes. This granular understanding could further refine allocation algorithms and optimize patient selection criteria.
Broader Context in Transplant Medicine
Lung transplantation remains a life-saving intervention for patients with end-stage pulmonary disease, but organ scarcity has historically limited access. The success of the CAS system demonstrates how policy changes can maximize the benefit of available donor organs while maintaining equity across diverse patient populations.
The study's findings provide compelling evidence that medical need-based allocation systems can achieve superior outcomes compared to geographic proximity models, potentially informing allocation strategies for other solid organ transplants.
