Lung Transplant Waitlist Outcomes Improved After 2023 Allocation System Change

Waitlist outcomes have significantly improved since the implementation of new allocation guidelines for lung transplants that prioritize medical urgency, according to findings from a recent study.1

The data were presented at the American Thoracic Society (ATS) International Conference 2025 and highlight improved outcomes following the implementation of United Network for Organ Sharing (UNOS) Composite Allocation Score (CAS) in 2023, especially among the sickest patients awaiting lung transplantation.1

Recent years have seen several changes in donor lung allocation in an effort to improve fairness and waitlist outcomes. Prior to November 2017, donor organs were allocated locally before being offered beyond the OPO. After a lawsuit in 2017, the allocation unit expanded to 250 nautical miles and the United Network for Organ Sharing (UNOS)/Organ Procurement and Transplantation Network began designing a new continuous allocation system. In March 2023, UNOS implemented the CAS to help consider patient factors when determining allocation of donor lungs.2

“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,” first author Mary Raddawi, MD, said in a press release.3 “This provides confirmation that we’re on the right track.”

Raddawi and colleagues conducted a retrospective cohort study using the UNOS registry. They created 3 cohorts from the 24,368 patients listed since February 19, 2015: Pre-November 2017 era (Cohort 1), post-November 2017 era (November 2017 - March 2023; Cohort 2) and CAS era (March 2023 - March 2024; Cohort 3). They additionally categorized patients into groups based on the waitlist urgency (WLU) score at listing: the top 5% WLU, use of High-flow nasal-cannula (HFNC) and bottom 25% of medical WLU.1

In the pre-November 2017 era, 11.2% of patients on the waitlist died/delisted, compared with 8.4% in the post-November 2017 era and 4.1% in the CAS era. In patients with the top 5% of WLU scores at listing, 34.5% of patients died/delisted in the pre-November 2017 era, compared with 22.2% in the post-November 2017 era and 6.5% in the CAS era.1

In an adjusted model, the pre- and post-November 2017 eras were associated with 3.3-fold and 2.1-fold increased risk of death/delisting compared to the CAS era (sHR, 3.32; 95% CI, 2.74-4.02; P <.001 and sHR, 2.10; 95% CI, 1.75-2.52; P <.001). For patients in the top 5% of WLU at listing, investigators noted the pre- and post-November 2017 eras were associated with 8-fold and 4.8-fold increased risks of death/delisting compared to the CAS era (sHR, 7.97; 95% CI, 3.72-17.1; P <.001 and sHR, 4.8; 95% CI, 2.29-10.15; P <.001).1

Investigators also pointed out patients on HFNC at listing had an increased risk of death/delisting in the prior eras compared to the CAS era (sHR, 7.68; 95% CI, 5.54-10.64; P <.001 and sHR, 5.28; 95% CI, 3.92-7.12; P <.001).1

“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 said.3

References

1. Raddawi M, Laothamatas K, Grewal HS, et al. Improvement in Wait List Mortality for the Most Critically Ill Since the Implementation of the CAS. Abstract presented at the American Thoracic Society (ATS) International Conference 2025 in San Francisco, CA, from May 18 - May 21, 2025.

2. UNOS. Lung Composite Allocation Score (CAS) calculator available on OPTN website. February 2, 2023. Accessed May 18, 2025. https://unos.org/news/lung-composite-allocation-score-cas-calculator-available-on-optn-website/.

3. Newswise. Waitlist Deaths Dropped Under New Lung Transplant Allocation System. American Thoracic Society. May 18, 2025. Accessed May 18, 2025. https://www.newswise.com/articles/waitlist-deaths-dropped-under-new-lung-transplant-allocation-system.