Diffuse Lung Disease and Lung Transplant Network
Lung Transplant Section
In March 2023, the Composite Allocation Score (CAS) will replace the Lung Allocation Score (LAS) for matching donor lungs to transplant candidates in the United States. The LAS was implemented in 2005 to improve lung organ utilization. Its score was determined by two main factors: (1) risk of 1-year waitlist mortality and (2) likelihood of 1-year post-transplant survival, with the first factor having twice the weight. However, LAS did not account for candidate biology attributes, such as pediatric age, blood type, allosensitization, or height. Long-term survival outcomes under LAS may be reduced, given the greater emphasis on waitlist mortality. Candidates were also subjected to strict geographical distributions within a 250-nautical-mile radius, which frequently resulted in those with lower LAS obtaining a transplant. CAS differs from the LAS in that it assigns an allocation score in a continuous distribution based on the following factors: medical urgency, expected survival benefit following transplant, pediatric age, blood type, HLA antibody sensitization, candidate height, and geographical proximity to the donor organ. Each factor has a specific weight, and because donor factors contribute to CAS, a candidate’s score changes with each donor-recipient match run. Continuous distribution removes hard geographical boundaries and aims for more equitable organ allocation. To understand how allocation might change with CAS, Valapour and colleagues created various CAS scenarios using data from individuals on the national transplant waiting list (Am J Transplant. 2022;22:2971).
They found that waitlist deaths decreased by 36%-47%. This effect was greatest in scenarios where there was less weight on placement efficiency (ie, geography) and more weight on post-transplant outcomes. Transplant system equity also improved in their simulation models. It will be exciting to see how candidate and recipient outcomes are affected once CAS is implemented.
Gloria Li, MD
Keith Wille, MD, MSPH
1. United Network for Organ Sharing. www.unos.org.